GROWTH AND CHARACTERIZATION OF

NONLINEAR OPTICAL 4-APMP, AMINO ACIDS

DOPED NaAP AND DGBCM SINGLE CRYSTALS

A THESIS

Submitted by

G. MARUDHU

Under the guidance of

Dr. S. KRISHNAN

in partial fulfilment for the award of the degree of

DOCTOR OF PHILOSOPHY in

PHYSICS

B.S.ABDUR RAHMAN UNIVERSITY (B.S. ABDUR RAHMAN INSTITUTE OF SCIENCE & TECHNOLOGY)

(Estd. u/s 3 of the UGC Act. 1956) www.bsauniv.ac.in

MARCH 2015

iv

B.S.ABDUR RAHMAN UNIVERSITY

(B.S. ABDUR RAHMAN INSTITUTE OF SCIENCE & TECHNOLOGY) (Estd. u/s 3 of the UGC Act. 1956)

www.bsauniv.ac.in

BONAFIDE CERTIFICATE

Certified that this thesis GROWTH AND CHARACTERIZATION OF

NONLINEAR OPTICAL 4-APMP, AMINO ACIDS DOPED NaAP AND

DGBCM SINGLE CRYSTALS is the bonafide work of MARUDHU. G

(RRN: 1090206) who carried out the thesis work under my supervision.

Certified further, that to the best of my knowledge the work reported herein

does not form part of any other thesis report or dissertation on the basis of

which a degree or award was conferred on an earlier occasion on this or any

other candidate.

SIGNATURE SIGNATURE

Dr. S. KRISHNAN Dr. I. RAJA MOHAMED RESEARCH SUPERVISOR PROFESSOR & HEAD Assistant Professor (Sr.Gr) Department of Physics Department of Physics B. S. Abdur Rahman University B. S. Abdur Rahman University Chennai – 600 048 Chennai – 600 048

ii

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v

ACKNOWLEDGEMENT

First of all, I am truly grateful to my supervisor

Dr. S. Krishnan, Assistant Professor of Physics, B. S. Abdur Rahman

University, Chennai who has been tremendously cooperative throughout my

research.

My sincere thanks to the Doctoral Committee members

Dr. R. Gopalakrishnan, Associate Professor of Physics, Anna University,

Chennai-25 and Dr. S.S.M. Abdul Majeed, Professor and Head, Department

of Polymer Technology, B. S. Abdur Rahman University, Chennai for their

critical comments and suggestions for my research work.

I am thankful to Dr. I. B. Shameem Banu, Dean (School of Physical

and Chemical Sciences) and Professor of Physics, B. S. Abdur Rahman

University, Chennai.

I express my heartfelt thanks to Dr. I. Raja Mohamed, Professor and

Head, Department of Physics, B. S. Abdur Rahman University, Chennai.

I place a record of thanks to The Principal, and the management of

Sri Ramanujar Engineering College, Chennai, for giving an opportunity to

teaching as an Assistant Professor in the Department of Physics, in this

esteemed institution.

It is my great pleasure to thank Dr. G. Vinitha, Assistant Professor of

Physics, School of Basic sciences, VIT University, Chennai.

I sincerely thank to Dr. P. Samuel, Assistant Professor, Department of

Physics, Ramco College of Engineering, Palayamkottai.

I am whole heartedly thank to Mr. G.V. Vijayaraghavan, Assistant

Professor (Sel. Grade), Department of Physics, B. S. Abdur Rahman

University, Chennai, for his constant support and encouragement throughout

my research work.

vi

I am always thankful to Dr. R. Indirajith, Assistant Professor,

Department of physics, B. S. Abdur Rahman University, Chennai, for his

tireless and moral support throughout my research work.

I am deeply indebted to Dr. M. Basheer Ahamed, Mr. S. Sathik

Basha, Mrs. U. Majitha Parvin, Mr. Md. Sheik Sirajuddeen, Dr. S. Begam

Elavarasi, Dr. J. Thirumalai, Dr. Jahir Abbas Ahmed and all non

teaching staff, Department of Physics, B. S. Abdur Rahman University,

Chennai, for their constant encouragement and support.

I am also thankful to Mr. T. Thilak, Mr. G. Shanmuganadhan,

Mr. R. Krishnan and all research scholars in the department of physics,

B. S. Abdur Rahman University, Chennai, for their help and support rendered

towards my research work.

I am truly grateful to Dr. G. Pasupathi, Assistant Professor of Physics,

Department of Physics, A.V.V.M. Sri Pushpam College, Thanjavur.

I wholeheartedly express my immense gratitude to my beloved

parents Mr. M. Gangatharan, Mrs. G. Kanniammal, my lovable wife

Mrs. Sudha, my cute son Jr. M. S. Thamizh, my uncle Mr. S. Balamurugan

and my Lovable sisters Mrs. Mala and her gifted son

Jr. B. M. Prahatheeshwaran, and Miss. Malar for their unlimited love,

boundless affection and support and blessings.

I thankfully remember to my uncle Mr. G. Vijayamohan, who is like

my father, my aunt Mrs. V. Senthamarai, who is like my mother and his

family for their huge support and encouragement to complete my research.

I must mention the huge encouragement received from my wonderful

B. Tech IT (2010-14) students of Sri Ramanujar Engineering College.

Finally, I thank all those who helped me directly or indirectly to

complete the research work in time.

G. MARUDHU

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ABSTRACT

Nonlinear optical 4-aminopyridinium monophthalate (4-APMP) single

crystals were grown by the slow evaporation technique using methanol as

the solvent. Single crystal X-ray diffraction confirmed that the grown crystal

belonged to the orthorhombic system. The presence of functional groups

was qualitatively determined by FTIR. The optical absorption studies

revealed very low absorption over the entire visible region. The fluorescence

spectrum at 430 nm indicated blue light emission. The thermal stability of the

grown crystal was found to be approximately 197.2˚C. Microhardness

studies revealed that the hardness number was 4.89. The second harmonic

generation (SHG) efficiency of the grown crystal was found to be 1.1 times

that of KDP crystals.

Amino acid-doped sodium acid phthalate (NaAP) crystals were

successfully grown by the slow evaporation technique at room temperature.

The effect of amino acids on the growth and properties of NaAP was

investigated thoroughly. Single crystal X-ray diffraction was carried out on the

grown crystals to identify the structural and lattice parameters. The presence

of dopants in NaAP single crystals was determined qualitatively by FTIR.

The optical transparency for the doped crystals was observed using optical

absorption. The mechanical strength of the grown crystals was determined

by Vickers microhardness measurements. The SHG efficiency for the grown

crystals was determined using the Kurtz powder technique.

Nonlinear optical single crystals of diglycine barium chloride

monohydrate (DGBCM) were grown by the slow evaporation solution growth

technique from a mixture of an aqueous solution of glycine and barium

chloride in the ratio 2:1 at room temperature. The grown crystals were

characterized by various techniques such as single crystal X-ray diffraction,

FTIR, UV-Vis-NIR spectra, Vickers hardness testing, thermogravimetric

analysis, and fluorescence spectra. Their SHG efficiency was measured by

the Kurtz and Perry powder technique using a Nd:YAG laser, and the results

were discussed in detail.

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TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ACKNOWLEDGEMENT v

ABSTRACT vii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF SYMBOLS xvii

1. INTRODUCTION 1

1.1 INTRODUCTION TO CRYSTAL GROWTH 1

1.2 IMPORTANCE OF NLO CRYSTALS 2

1.3 INORGANIC CRYSTALS 4

1.4 ORGANIC CRYSTALS 5

1.5 SEMIORGANIC CRYSTALS 6

2. LITERATURE OVERVIEW 8

2.1 INTRODUCTION 8

2.2 4-AMINOPYRIDINIUM MONOPHTHALATE

(4-APMP) SINCLE CRYSTAL 8

2.3 AMINO ACID DOPED SODIUM ACID

PHTHALATE (NaAP) SINGLE CRYSTALS 9

2.4 DIGLYCINE BARIUM CHLORIDE

MONOHYDRATE (DGBCM) SINGLE

CRYSTAL 9

2.5 CONCLUSION 10

3. EXPERIMENTAL 12

3.1 INTRODUCTION 12

3.2 MATERIALS 12

3.3 GLASSWARE AND APPARATUS 13

3.4 MATERIAL SYNTHESIS 13

ix

CHAPTER NO. TITLE PAGE NO.

3.4.1 SYNTHESIS OF 4-AMINOPYRIDINIUM

MONOPHTHALATE 13

3.4.2 SYNTHESIS OF AMINO ACID DOPED

SODIUM ACID PHTHALATE 14

3.4.3 SYNTHESIS OF DIGLYCINE BARIUM

CHLORIDE MONOHYDRATE 20

3.5 CHARACTERIZATIONS 21

3.6 CONCLUSION 21

4. STRUCTURAL, OPTICAL,

FLUORESCENCE, MECHANICAL AND

THERMAL PROPERTIES OF NONLINEAR

OPTICAL 4-AMINOPYRIDINIUM

MONOPHTHALATE SINGLE CRYSTAL 22

4.1 INTRODUCTION 22

4.2 RESULTS AND DISCUSSION 22

4.2.1 Single crystal X-ray diffraction analysis 22

4.2.2 FTIR Spectral Study 25

4.2.3 Optical Absorption Spectral Studies 25

4.2.4 Fluorescence Studies 27

4.2.5 Thermal analysis 28

4.2.6 Microhardness studies 29

4.2.7 NLO studies 34

4.3 CONCLUSION 35

5. OPTICAL AND MECHANICAL STUDIES

ON AMINO ACID DOPED SODIUM

ACID PHTHALATE (NaAP) SINGLE

CRYSTALS 36

5.1 INTRODUCTION 36

5.2 RESULTS AND DISCUSSION 36

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CHAPTER NO. TITLE PAGE NO.

5.2.1 Single crystal X-ray diffraction analysis 36

5.2.2 FTIR studies 38

5.2.3 UV-vis-NIR spectral analysis 40

5.2.3.1 Determination of Optical Constants 44

5.2.4 Microhardness measurements 51

5.2.5 Nonlinear Optical studies 53

5.3 CONCLUSION 54

6. STRUCTURAL, OPTICAL, MECHANICAL,

THERMAL AND FLUORESCENCE

PROPERTIES OF NONLINEAR OPTICAL

DIGLYCINE BARIUM CHLORIDE

MONOHYDRATE (DGBCM)

SINGLE CRYSTAL 55

6.1 INTRODUCTION 55

6.2 RESULTS AND DISCUSSION 55

6.2.1 Single crystal X-ray diffraction analysis 55

6.2.2 FTIR studies 57

6.2.3 Optical absorption studies 58

6.2.3.1 Determination of Optical Constants 60

6.2.4 Microhardness studies 62

6.2.5 TGA/DTA studies 66

6.2.6 Fluorescence studies 66

6.2.7 Second harmonic generation study 67

6.3 CONCLUSION 68

7. CONCLUSION 69

xi

CHAPTER NO. TITLE PAGE NO.

8. SCOPE FOR FURTHER WORK 71

REFERENCES 72

APPENDIX 1

(BASIC CONCEPTS) 95

APPENDIX 2

(PREPARATION TECHNIQUES) 99

APPENDIX 3

(CHARACTERIZATION TECHNIQUES) 108

TECHNICAL BIOGRAPHY 118

xii

LIST OF TABLES

TABLE

NO. TITLE PAGE NO.

4.1 Crystal data and structure refinement for 4-APMP 24

4.2 FTIR analysis of the grown crystal 26

4.3 Microhardness value obtained on the 4-APMP crystal 34

5.1 Lattice parameters for Pure and doped crystals 37

6.1 Some theoretical parameters on DGBCM crystals 57

6.2 Microhardness value obtained on the DGBCM crystal 65

6.3 Comparative of SHG efficiencies of NLO crystals

relative to KDP 68

A.1.1 Seven Crystal Systems 97

xiii

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

3.1 Photograph of as grown 4-APMP crystal 14

3.2 Photograph of Pure NaAP crystal 15

3.3

Photograph of NaAP crystal doped with 1 mol%

L-alanine 15

3.4

Photograph of NaAP crystal doped with 3 mol%

L-alanine 16

3.5

Photograph of NaAP crystal doped with 5 mol%

L-alanine 16

3.6

Photograph of NaAP crystal doped with 1 mol%

L-arginine 17

3.7

Photograph of NaAP crystal doped with 3 mol%

L-arginine 17

3.8

Photograph of NaAP crystal doped with 5 mol%

L-arginine 18

3.9 Photograph of NaAP crystal doped with 1 mol% Glycine 18

3.10 Photograph of NaAP crystal doped with 3 mol% Glycine 19

3.11 Photograph of NaAP crystal doped with 5 mol% Glycine 19

3.12 Photograph of as grown DGBCM crystal 20

4.1 Molecular structure of 4-APMP crystal 23

4.2 FTIR spectrum of the grown crystal 25

4.3 Optical absorption spectrum the grown crystal 27

4.4 Emission Spectrum of 4-APMP crystal 28

xiv

FIGURE NO. TITLE PAGE NO.

4.5 TG-DTA spectrum of the title crystal 29

4.6 Plot of load (P) vs. Hv 30

4.7 Plot of Log d vs. log P 30

4.8 Plot of dn vs. Load P 31

4.9 Plot of d vs. dn/2 32

4.10 P vs. σv

33

4.11 P vs C11

33

5.1 FTIR Spectra of L-alanine doped NaAP crystals 39

5.2 FTIR Spectra of L-arginine doped NaAP crystals 39

5.3 FTIR Spectra of Glycine doped NaAP crystals 40

5.4 Absorption spectra of L-alanine doped NaAP crystals 41

5.5 Absorption spectra of L-arginine doped NaAP crystals 41

5.6 Absorption spectra of Glycine doped NaAP crystals 42

5.7 Plot of (αhν) 2 vs. (hν) for pure and L-alanine doped

NaAP crystals 43

5.8 Plot of (αhν) 2 vs. (hν) for pure and L-arginine doped

NaAP crystals 43

5.9 Plot of (αhν) 2 vs. (hν) for pure and Glycine doped

NaAP crystals 44

5.10 Extinction Coefficient of L-alanine doped NaAP crystals 45

xv

FIGURE NO. TITLE PAGE NO.

5.11 Extinction Coefficient of L-arginine doped NaAP crystals 46

5.12 Extinction Coefficient of Glycine doped NaAP crystals 46

5.13 Reflectance of L-alanine doped NaAP crystals 47

5.14 Reflectance of L-arginine doped NaAP crystals 47

5.15 Reflectance of Glycine doped NaAP crystals 48

5.16 Optical Conductivity of L-alanine doped NaAP crystals 48

5.17 Optical Conductivity of L-arginine doped NaAP crystals 49

5.18 Optical Conductivity of Glycine doped NaAP crystals 49

5.19 Electrical Conductivity of L-alanine doped NaAP

crystals

50

5.20 Electrical Conductivity of L-arginine doped NaAP

crystals

50

5.21 Electrical Conductivity of Glycine doped NaAP crystals 51

5.22 Hardness number of L-alanine doped NaAP crystals 52

5.23 Hardness number of L-arginine doped NaAP crystals 52

5.24 Hardness number of Glycine doped NaAP crystals 53

5.25 SHG efficiency of doped amino acid crystals 54

6.1 FTIR spectrum of the grown crystal 58

6.2 Optical absorption spectrum of the grown crystal 59

6.3 Plot of (hν) vs. (αhν) 2 60

xvi

FIGURE NO. TITLE PAGE NO.

6.4 Plot of extinction coefficient (K) vs. photon energy (hν) 61

6.5 Plot of photon energy (hν) vs. Refractive index (n) 61

6.6 Plot of P vs. Hv 62

6.7 Plot of Log d vs. log P 63

6.8 Plot of dn vs. Load P 64

6.9 Plot of d vs. dn/2 64

6.10 TG/DTA analysis of the title crystal 66

6.11 Fluorescence spectrum of the DGBCM crystal 67

A.2.1 Mason jar crystallizer 106

A.3.1 Powder X-ray Diffractometer 109

A.3.2 Schematic diagram of a FTIR spectrometer 111

A.3.3 Schematic representation of a UV-Vis-NIR

spectrophotometer 112

A.3.4 Second Harmonic Generation (SHG) Instrument 118

xvii

LIST OF SYMBOLS AND ABBREVIATIONS

XRD - X-ray diffraction

FTIR - Fourier Transform Infrared

KBr - Potassium Bromide

UV - Ultraviolet

NIR - Near Infrared

TGA - Thermogravimetric Analysis

DTA - Differential Thermal Analysis

NLO - Nonlinear Optics

SHG - Second Harmonic Generation

Nd : YAG - Neodymium Yttrium Aluminium Garnet

Eg - Energy gap

h - Planck’s constant

σelec - Electrical conductivity

n - Refractive index

K - Extinction coefficient

P - Polarization

HV - Vickers hardness number

nm - Nanometre

Å - Angstrom

KDP - Potassium Dihydrogen Phosphate

120

LIST OF INTERNATIONAL PUBLICATIONS

[1] Marudhu G, Krishnan S, Thilak T, Samuel P, Vinitha G, and

Pasupathi G, “Growth, thermal and optical studies on nonlinear

optical material Diglycine Barium Chloride Monohydrate (DGBCM)

single crystal”, Journal of Nonlinear Optical Physics & Materials,

Vol. 22, pp. 1-13, 2013.

[2] Marudhu G, Krishnan S, and Vijayaragavan G. V, “Optical, theoretical

and mechanical studies on sodium acid phthalate crystal”, Optik,

Vol. 125, pp. 2417-2421, 2014.

LIST OF PAPERS COMMUNICATED IN INTERNATIONAL JOURNALS

[1] Marudhu G, Krishnan S, and Vijayaragavan G. V, “Optical and

mechanical studies on Amino acids doped Sodium acid phthalate

(NaAP) single crystals by slow evaporation method” to Journal of

Optoelectronics and Advanced Materials-Rapid Communications.

[2] Marudhu G, Krishnan S, and Palanichamy M, “Growth, structural,

optical, thermal and mechanical studies on 4-Aminopyridinium

monophthalate: A novel nonlinear optical crystal” to Journal of Optics

and Laser Technology.

121

LIST OF PRESENTATIONS IN NATIONAL CONFERENCE/SEMINAR

[1] Marudhu G, Thilak T and Vinitha G, “Growth and Characterization of

KDP crystals in different pH values by Solution Growth method” in the

Padiga Valarchi Ariviyal Karutharangu, conducted by Anna University,

Chennai, held on 18-19 October, 2010.

[2] Marudhu G, Krishnan S, Vinitha G and Vijayaragavan G. V, “Growth,

optical, thermal and mechanical properties of nonlinear optical sodium

acid phthalate single crystal by slow evaporation technique” in the

XVIII NATIONAL SEMINAR ON CRYSTAL GROWTH (XVIII NSCG-

2014), conducted by SSN Engineering College, Chennai-603 110,

held on 24-26 October, 2014.

[3] Marudhu G and Krishnan S, “Growth and Characterizations of

Nonlinear Optical Diglycine Barium Chloride Monohydrate (DGBCM)

single crystal” in the Second National conference on Recent advances

in materials (NCRAM-2014), conducted by B.S.Abdur Rahman

University, Chennai, held on 03-04 September, 2014.

72

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pp.119-124, 2008.

[154] Marudhu G, Krishnan S, Vijayaragavan G. V, “Optical, theoretical and

mechanical studies on sodium acid phthalate crystal”, Optik, Vol. 125,

pp. 2417-2421, 2014.

[155] Marudhu G, Krishnan S, Thilak T, Samuel P, Vinitha G, and

Pasupathi G, “Growth, thermal and optical studies on nonlinear

optical material Diglycine Barium Chloride Monohydrate (DGBCM)

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93

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94

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pp. 3798-3813, 1968.

1

1. INTRODUCTION

1.1 INTRODUCTION TO CRYSTAL GROWTH

Many modern technological devices would not exist without the use of

synthetic single crystals, obtained by the technique for preparing and

producing bulk single crystals known as crystal growth [1]. Crystal growth

has consistently been a key aspect in some of the most important advances

of the past 80 years. Crystal growth is an applied science that underpins a

number of the world’s major industries because the accomplishments of most

of the extraordinary modern day technologies are very much attributed to the

development of microelectronic, optoelectronic and optical devices made

from artificial crystals [2, 3]. The most in demand research area in the field of

physics is crystal growth; currently, it addresses how to grow crystals and

what their properties are, as well as how they can be suitably fabricated for

device applications. The above questions were answered by developing

novel nonlinear optical (NLO) crystals for a wide range of applications such

as optical switching, frequency conversion and electro-optic modulation [4].

The crystalline quality of NLO crystals must be improved to be able to

fabricate large single crystals for fruitful applications [5]. Here, crystal

engineering involves the development of new crystalline materials with

superior properties, functions and applications, e.g., polarized materials for

NLO applications and materials tailored with magneto-photo properties such

as luminescence for electronic applications and molecular sensors [6]. In

chemistry, the compositions of crystals are based on atomic and molecular

concepts. In particular, X-ray diffraction has been used to reveal the internal

structure of single crystals.

Materials science is primarily concerned with the fundamental

understanding of the internal structure, properties and processing of

materials and is ultimately responsible for many of the recent technological

innovations [7]. Thus, crystals are considered the pillars of modern

technology. In recent years, crystals have been used in the development of

2

photonics technology, which uses both electrons and photons to carry, store

and process information [8-12]. Crystals are also typically used in laser

technology, optoelectronics, photovoltaic devices, infrared detectors and

other technologically important scientific applications [13-15].

A single crystal or monocrystalline solid is a material in which the

crystal lattice of the entire sample is continuous with no grain boundaries.

This allows the material to exhibit unique properties, in particular mechanical,

optical and electrical properties, which can be anisotropic depending on the

crystal structure. Anisotropic crystals can be obtained if the origin of the

crystal growth is along a single direction. The additional free energy for each

crystal growth volume can be determined from the interface types and the

final size of the crystal and is an important factor for the mechanical

properties. Anisotropy is useful in single crystals of silicon, used in

semiconductor industries, especially in semiconductor fabrication and

functioning field effect transistors, for altering local electrical properties. The

importance of single crystals in various applications is evident from the recent

advancements in the fields of semiconductors; polarizers; transducers;

infrared detectors; ultrasonic amplifiers; ferrites; magnetic garnets; solid state

lasers; nonlinear optic, piezoelectric, acousto-optic, and photosensitive

materials; and crystalline thin films used in microelectronics and hardware

industries [16-18]. Hence, to achieve high performance devices, high quality

single crystals are needed. The growth and characterization of single

crystals for device fabrication have created a great stimulus due to their

significance for both academic and applied research.

1.2 IMPORTANCE OF NLO CRYSTALS

The appropriate development of crystal growth is nonlinear optics,

which means the extension of the motion of the linear propagation of an

electromagnetic field. In mathematics, this is based on Maxwell’s equations,

in which the polarization of a medium is expressed in terms of a power series

[19]. In recent years, great efforts have been made in the field of nonlinear

optics through investigating several classes of materials, including organic,

3

inorganic, and semiorganic, which are expected to be important for

optoelectronics, frequency conversion effects, high speed information

processing, optical advantages such as optical data storage technology, etc.

[20, 21] Here, NLO materials are a special criteria class of the materials,

which have a huge impact on laser and information technology and industrial

applications because of their ability to change the frequency of an incoming

laser beam by modifying its amplitude and phase [22]. Therefore, lasers

alone cannot be used widely in modern science and technology without NLO

crystals [23]. Hence, the development of NLO crystals with better linear

optical (LO) and NLO properties, wider spectral transmission and phase-

matching range is obviously essential for further broadening the applications

of lasers such as image applications, frequency multipliers, mixers,

parametric oscillators, and other functions in the deep-UV, far IR, and even

THz spectral regions [24].

Finally, our aim is to develop novel materials with large nonlinearities

that exhibit exceptional properties such as a wide transparency range, fast

response in data processing, and high damage threshold [25-27]. For this,

we grew and fabricated application-oriented crystals by mixing various

materials into grown NLO materials. Some materials could allow the entry of

light depending on the orientation at room temperature, i.e., receiving high

energy of photons in the blue and green range from incident infrared light

through a NLO crystal [28-30]. Some of the familiar crystals that exhibit the

property of frequency conversion over the entire UV and visible regions are

KTP, LBO, BBO, KDP, KNbO3, LiNbO3, AgGaS2, AgGaSe2, etc. These

crystals are selected based on their optical, mechanical, and physical

properties, such as transmission, damage threshold, and efficiency of the

nonlinear effect, phase matching range and laser beam quality [31, 32].

In the current decade, many researchers have focused on the growth

and characterization of aminopyridine groups to establish NLO behaviour

[33]. The slow evaporation technique is used to grow NLO crystals with good

optical transparency, better orientation, defect-free structures, and good

mechanical and thermal stability [34].

4

1.3 INORGANIC CRYSTALS

Inorganic materials are preferred for NLO applications over organic

materials. The single crystals of pure inorganic materials, such as quartz,

lithium niobate (LINbO3), potassium dihydrogen phosphate (KDP), potassium

titanyl phosphate (KTP), and urea, exhibit excellent NLO properties. These

are the pure inorganic materials used in second harmonic generating

devices, parametric oscillators, etc. [35-39]. Some of the familiar properties

of inorganic host materials are large mechanical strength, excellent thermal

stability, good transmittance, and high electro-optic coefficients as well as

high degree of chemical inertness [40-43]. The most familiar single crystals

of KDP exhibit superior NLO properties and have been used as reference

materials for comparison with other crystalline materials. The transmittance,

hardness and dielectric constants are improved by growing KDP crystals

using the Sankaranarayanan-Ramasamy method compared with the normal

slow evaporation method [44, 45]. NLO materials such as lithium sulphate,

potassium lithium niobate and lithium triborate have peculiar advantages

such as a large damage threshold, high phase matching angle, wider

transparency range and chemical stability. Additionally, lithium sulphate

monohydrate has been classified as a promising material for Raman laser

frequency converters [46]. We have been growing several inorganic

materials that exhibit high transparency, good chemical stability and tensile

strength as well as second harmonic generation (SHG), frequency

conversion, optical parametric amplification (OPA), optical parametric

oscillation (OPO), optical emission [47] and electro-optical applications.

However, in these systems, the nonlinear responses are undoubtedly related

to individual bond polarizabilities. Due to a lack of extended π electron

delocalization, the inorganic materials have modest optical nonlinearities.

Due to the difficulty of synthesizing towards particular directions, newer

materials are currently being explored, and this has led to a new class of

NLO materials [48].

5

1.4 ORGANIC CRYSTALS

Organic materials exhibit excellent NLO properties because of their

electronic structure with π conjugated systems between donors and

acceptors [49, 50]. This is due to non-centrosymmetry leading to huge NLO

efficiency, exhibited by organic materials on the order of 10 to 100 times

larger than that of inorganic NLO materials through macroscopic second

order NLO response [51]. These materials exhibit excellent properties such

as optoelectric coefficients, large second-order NLO coefficients, small

dielectric constants, molecular designing, faster optical responses, and ultra-

fast responses to external electric fields. [52]. Hence, organic materials are

superior to their inorganic counterparts in terms of crystal preparation, device

fabrication, and production of better devices with large nonlinearities, i.e.,

they have wide applications in areas such as information storage, optical

communication, optical data storage, optoelectronics, laser technology, and

telecommunications [53]. Moreover, they can be in bulk and single form for

NLO device fabrication. Additionally, they are important for frequency

modulation device applications, such as frequency conversion, integrated

circuitry, optical switching, and terahertz wave generation with detection [54].

The slow evaporation technique is one of the simplest techniques for growing

high quality organic single crystals [55]. Recently, Paul M. Dinakaran had

grown 4-Bromo 4-nitrostilbene (BONS) single crystals that exhibited a peak

NLO efficiency of 67 times greater than the reference KDP crystal [25].

Another organic host crystal L-phenylalanine-4-nitrophenol (LPAPN)

demonstrated a high NLO efficiency of 1.2 times that of KDP [50]. One of the

newest organic NLO materials is thiourea with quinine sulphate dehydrate

(TQS) grown by the gel method by Lekshmi P. Nair. This exhibited 1.4 times

higher NLO behaviour than the KDP reference crystal [54]. Redrothu

Hanumantharao had grown l-threonine formate, which had an SHG efficiency

of 1.21 times that of reference KDP [56]. Even though organic materials

have many advantages, they exhibit some drawbacks, as they have a low

laser damage threshold, low optical transparency, etc. [57].

6

1.5 SEMIORGANIC CRYSTALS

The inability of organic materials to grow to large crystal sizes

impedes device fabrication, which has led to the discovery of a new class of

crystals called semi organics to satisfy technological requirements [58, 59].

The most promising candidates among metal-organic compounds have

attracted researchers in recent years due to their various properties such as

NLO response, magnetism, and luminescence, as well as applications in

photography and drug delivery [6] due to the combination of organic and

inorganic components. Hence, they have shown large NLO behaviour and

also favourable properties such as high optical transparency over the entire

visible region, a large laser damage threshold value, low deliquescence, high

resistance, and low angular sensitivity [4, 21].

In semiorganic materials, the organic ligand is ionically bonded with

the inorganic host, which promotes exceptional mechanical strength and

chemical stability [42]. Because of this, semiorganic materials are promising

for many other applications such as frequency conversion, light amplitude

and phase modulation and phase conjugation [60]. One significant example

of semiorganic hosts is alkali hydrogen phthalate single crystal, which is used

in long-wave X-ray spectrometers. Several semi organics are used as

substrates for depositing thin films of organic NLO samples, and their

centrosymmetric or non-centrosymmetric forms depend on how the cations

are arranged in the chemical bonding during crystal growth [52] and are thus

suitable for the fabrication of optoelectronic devices [61]. Moreover, metal–

organic complexes offer higher environmental stability combined with greater

diversity of tunable electronic properties by virtue of the coordinated metal

centre [6]. Furthermore, organic ligands combined with inorganic hosts

thereby become semiorganic crystals, which lead to more attractive

applications such as SHG, THG, optical bistability, laser remote sensing,

optical disc data storage, laser driven fusion, medical and spectroscopic

image processing, colour displays and optical communication [33].

7

Recently, Soma Adhikari grew L-leucine hydrobromide (LEHBr) single

crystals, which demonstrated a peak NLO efficiency 4 times greater than that

of reference KDP [61]. Another semiorganic host crystal, bis (thiourea) silver

(I) nitrate (TuAgN), exhibited a better NLO efficiency of 0.85 times that of

KDP [58]. Another NLO material, 2-aminopyridine bis thiourea zinc sulphate,

was grown by the slow evaporation method. This exhibited higher NLO

behaviour than KDP [33].

8

2. LITERATURE OVERVIEW

2.1 INTRODUCTION

Currently, most of the published research has focused on semiorganic

crystals to enhance the nonlinear optical properties. Due to familiar

properties of both inorganic and organic hosts, until now, semiorganic

materials have been grown for more familiar broad applications, such as

frequency modulation, data storage technology, fibre optic communication,

optical modelling, and electro-optic modulations, because of their good

mechanical strength, high optical transmittance, large damage threshold,

chemical stability, etc. [62].

2.2 4-AMINOPYRIDINIUM MONOPHTHALATE (4-APMP) SINGLE

CRYSTAL

Pyridine and its derivatives of 4-aminopyridine are used as proton

acceptors. 4-Aminopyridine (4-NH2Py) has an amine group present in the

para-position of the nitrogen of the heterocycle. The phthalic acid is an

aromatic dicarboxylic acid group, which has two carboxylic groups in the

ortho positions so that it can act in bidentate ligand (COO-, COO-)

coordination, thereby acting as a donor in the nucleation process. In donor-

acceptor series, the organic ligands are favourable for growing NLO crystals

by the slow evaporation technique, in which one of the pyridine derivatives of

2-aminopyridine is combined with some of the organic ligands such as

benzoic acid, malic acid, etc. Work has been published on the well-known 2-aminopyridinium benzoate [63] and 2-aminopyridinium malate [64] single

crystals, which provides better information on the structural, functional,

optical, thermal, and mechanical properties, dielectric behaviour and

enhancements to the NLO properties. However, there are currently no

reports on the above properties for 4-aminopyridine combined with phthalic

acid, i.e., 4-aminopyridinium monophthalate single crystals produced by the

slow evaporation method. In the present work, the structural, optical,

thermal, mechanical and fluorescence properties of 4-aminopyridinium

9

monophthalate single crystals grown by slow evaporation are reported for the

first time.

2.3 AMINO ACID DOPED SODIUM ACID PHTHALATE (NaAP) SINGLE

CRYSTALS

The most significant phthalic acid families are potassium acid

phthalate (KAP) and sodium acid phthalate (NaAP) single crystals, which are

used for various scientific applications such as substrates for organic thin film

NLO materials [65], standards in volumetric analysis, etc. [66] Generally,

KAP crystals are discussed much more in the literature, while very limited

information is available on NaAP single crystals. These phthalate family

materials exhibit large optical transmission with low absorption over the entire

UV-visible region, superior thermal stability in the presence of moisture and

good mechanical hardness; moreover, photo-electric devices can be

fabricated to take advantage of their SHG behaviour [154]. One research

group has used zinc, an inorganic metal, as a dopant in NaAP single crystals

for the improvement of optical, thermal and dielectric properties [52].

Rigorous literature surveys reveal that amino acids are not used as dopants

in NaAP crystals. Hence, L-alanine, L-arginine and glycine are added as

dopants to NaAP single crystals. In the present work, we discuss the optical

and mechanical properties of pure and doped NaAP single crystals grown by

the slow evaporation technique.

2.4 DIGLYCINE BARIUM CHLORIDE MONOHYDRATE (DGBCM) SINGLE

CRYSTAL

Glycine is a simple and effective amino acid with a zwitterionic

structure. Its complexes with inorganic materials have attracted the attention

of many researchers [67]. Furthermore, they show high optical nonlinearity

as well as the chemical flexibility of organic materials and physical

ruggedness of inorganic materials [6]. Glycine zinc sulphate, glycine oxalic

acid, glycine nitrate, and glycine lithium sulphate are the stoichiometric ratio-

based NLO crystals. At an appropriate ratio of 2:1, glycine can be combined

10

with familiar inorganic materials, such as zinc chloride, cadmium chloride,

calcium bromide, and magnesium sulphate, and organic materials, such as

picric acid, oxalic acid and hydrochloric acid. These combinations have

enabled developments in bulk growth and have provided new structural,

optical, thermal, mechanical, dielectric and NLO properties. Here, we

mention that some of the diglycine derivatives, such as diglycine zinc chloride

(DGZC) NLO single crystals [68], diglycine cadmium chloride (DGCC) single

crystals [69], calcium dibromide bis (glycine) tetrahydrate single crystals [62],

diglycine hydrobromide NLO crystal [70], bisglycine oxalate single crystals

[71], and diglycine picrate single crystals [72], were grown by the slow

evaporation method. In the series of glycine derivatives we have

investigated, the familiar one is diglycine barium chloride single crystal, which

is a nonlinear optical semiorganic crystal with non-centrosymmetry belonging

to the orthorhombic crystal system. Some of the researchers who have

investigated this material have produced significant studies [73]. Studies

from the current decade are discussed in Chapter 6. The growth of diglycine

barium chloride monohydrate single crystals has been investigated to

improve their optical, mechanical and NLO properties for fabrication tailored

towards device applications.

2.5 CONCLUSION

From the above discussions, it is clear that growth, optical, thermal,

and mechanical studies of 2-aminopyridinium benzoate and 2-aminopyridinium malate single crystals have been conducted that use the

slow evaporation method. A rigorous literature survey reveals that nonlinear

optical 4-aminopyridinium monophthalate single crystals obtained from slow

evaporation were not reported elsewhere. Likewise, the addition of zinc to

NaAP single crystals has been reported elsewhere. However, amino acid-

doped (L-alanine, L-arginine and glycine) NaAP single crystals obtained by

slow evaporation have been reported for the first time by us. Additionally, the

growth and theoretical, optical, and mechanical properties of diglycine barium

chloride monohydrate single crystals obtained by slow evaporation have

been reported and published [155]. All of the above mentioned compounds

11

were subjected to various characterizations, and the results were discussed

in detail.

12

3. EXPERIMENTAL

3.1 INTRODUCTION

This chapter addresses the crystal growth technique, in particular the

slow evaporation solution growth technique. This technique is used to grow

a crystal in a simple manner and provide improvements in purity.

Additionally, this technique can produce organic, inorganic and semiorganic

NLO crystals at ambient temperature in different solvents. Hence, we chose

this technique to grow our crystals, including 4-aminopyridinium

monophthalate, amino acid-doped NaAP and diglycine barium chloride

monohydrate single crystals.

4-Aminopyridinium monophthalate (4-APMP) crystals based on

organic materials were subjected to many characterization studies to

measure their structural, vibrational, optical and mechanical properties.

Other work on semiorganic materials, such as amino acid-doped NaAP, has

demonstrated modifications to the optical and mechanical behaviours. The

final works were on diglycine barium chloride monohydrate (DGBCM) crystal

semiorganic materials; characterizations of these materials were carried out

to improve their physical properties. Hence, the experimental methods used

for the various types of crystals are briefly discussed in this chapter.

3.2 MATERIALS

4-aminopyridine

Phthalic acid

Sodium bicarbonate

L-alanine

L-arginine

Glycine

Barium chloride dihydrate

13

3.3 GLASSWARE AND APPARATUS

Magnetic stirrer

Magnetic pellets

Beakers

Whatmann filter paper

Tissue paper

Petri dish

Digital weight balance

3.4 MATERIAL SYNTHESIS

3.4.1 SYNTHESIS OF 4-AMINOPYRIDINIUM MONOPHTHALATE

The title compound was synthesized by dissolving (AR grade)

4-aminopyridine and phthalic acid in methanol in a 1:1 molar ratio. After

continuous stirring, the supersaturated solution was filtered with Whatmann

filter paper and kept it in a dust free atmosphere. The saturated solution was

allowed to dry at room temperature by the slow evaporation technique. After

a period of 30 days, optically transparent and defect free crystals with

dimensions of 15 × 3 × 2 mm3 were grown, and the photograph of the grown

crystal is shown in Fig. 3.1. The chemical reaction of the synthesized

materials is given as follows:

C5H6N2 + C8H6O4 → C13H12N2O4

14

Figure 3.1: Photograph of as grown 4-APMP crystal

3.4.2 SYNTHESIS OF AMINO ACID-DOPED SODIUM ACID PHTHALATE

The amino acid-doped NaAP single crystals were prepared by doping

1 mol%, 3 mol%, and 5 mol% of each amino acid (AR grade L-alanine,

L-arginine, and glycine) into NaAP in double distilled water at ambient

temperature and stirring thoroughly for five hours. The impurities were

removed by successive recrystallization. The supersaturated solutions were

filtered using Whatmann filter paper and were kept in dust free atmosphere.

15

Figure 3.2: Photograph of pure NaAP crystal

Figure 3.3: Photograph of NaAP crystal doped with 1 mol% L-alanine

16

Figure 3.4: Photograph of NaAP crystal doped with 3 mol% L-alanine

Figure 3.5: Photograph of NaAP crystal doped with 5 mol% L-alanine

17

Figure 3.6: Photograph of NaAP crystal doped with 1 mol% L-arginine

Figure 3.7: Photograph of NaAP crystal doped with 3 mol% L-arginine

18

Figure 3.8: Photograph of NaAP crystal doped with 5 mol% L-arginine

Figure 3.9: Photograph of NaAP crystal doped with 1 mol% Glycine

19

Figure 3.10: Photograph of NaAP crystal doped with 3 mol% Glycine

Figure 3.11: Photograph of NaAP crystal doped with 5 mol% Glycine

20

All 9 mixtures were allowed to undergo slow evaporation. L-alanine,

L-arginine, and glycine-doped NaAP crystals with different concentrations

were obtained within the periods of 22, 20, and 21 days, respectively. The

photographs of the doped NaAP crystals are shown in Figs. 3.2 - 3.11.

3.4.3 SYNTHESIS OF DIGLYCINE BARIUM CHLORIDE MONOHYDRATE

Diglycine barium chloride Monohydrate (DGBCM) salt was

synthesized by dissolving (AR grade) glycine and barium chloride dihydrate

in a 2:1 molar ratio in double distilled water. The supersaturated solution of

DGBCM was prepared and filtered using Whatmann filter paper. The filtered

solution was tightly closed with a thin plastic sheet, so that the rate of

evaporation could be minimized. After a period of 25 days, a colourless,

transparent crystal with dimensions of 10 x 8 x 2 mm3 was obtained and is

shown in Fig. 3.12.

(NH2CH2COOH)2 + BaCl2. 2H2O → Ba (NH2CH2COOH)2 Cl2. H2O

Figure. 3.12: Photograph of as grown DGBCM crystal

21

3.5 CHARACTERIZATIONS

There was various characterization techniques used to analyse the

grown crystals. A single crystal X-ray diffractometer was used to determine

the structure of the grown crystals. Fourier transform interferometry

confirmed the presence of functional groups in the crystalline materials.

Spectroscopic methods are widely used for qualitative and quantitative

analyses of chemical compounds. The UV-Vis-NIR spectrum gave the

optical transmittance and absorption of the grown crystals. The fluorescence

spectrum showed excitation and emission wavelengths for the crystalline

materials. Thermal analysis was used for studying the thermal stability of the

grown crystals. The Vicker’s hardness measurement was used for

investigating the mechanical behaviour of the grown crystals. The Kurtz and

Perry powder technique was used to find the SHG efficiency of the grown

crystals.

3.6 CONCLUSION

The various types of grown crystals were successfully prepared by the

slow evaporation solution growth technique. They exhibited superior

transparency without major imperfections. Hence, they were selected to

undergo further characterization, and the exhibited properties for each crystal

are reported in the upcoming chapters.

22

4. STRUCTURAL, OPTICAL, FLUORESCENCE, MECHANICAL

AND THERMAL PROPERTIES OF NONLINEAR OPTICAL

4-AMINOPYRIDINIUM MONOPHTHALATE SINGLE CRYSTAL

4.1 INTRODUCTION

In recent years, nonlinear optical materials (NLO) have attracted many

researchers due to its wide applications in the field of telecommunication,

optoelectronic and optical information storage devices [74-81]. Organic NLO

materials exhibits much larger NLO efficiencies compared to their inorganic

counterpart, thus promises to meet future requirements for ultrahigh

bandwidth photonic devices [82-84]. Organic materials have been known for

their potential applications in semiconductors, superconductors and nonlinear

optical devices [85]. Hence, Organic NLO crystals with high second

harmonic generation efficiency and transparency in UV-Vis region are

required for numerous device applications. In the present work, single

crystals of 4-Aminopyridinium monophthalate have been grown from

aqueous solution by slow evaporation technique and the grown crystals were

subjected to various characterizations such as single crystal XRD, FTIR, UV,

Fluorescence, thermal and mechanical analysis and the results were

discussed in detail.

4.2 RESULTS AND DISCUSSION

4.2.1 Single crystal X-ray diffraction analysis

The grown crystal having dimensions 0.35 x 0.30 x 0.25 mm3 was

subjected to single crystal XRD analysis using Enraf Nonius CAD 4/MACH 3

single crystal X-ray diffractometer using Mo Kα radiation (λ = 0.71073 Å).

The crystal structure of the title compound was solved by the direct method

using the program SIR-92 (WINGX) [86]. Data were collected in frames

using oscillation method with µ ranging between 2.59 and 25.00 θ. Full

matrix least-squares refinement was done using SHELXL-97 (WINGX)

computer program [87, 88].

23

Figure. 4.1: Molecular structure of 4-APMP crystal

Table 4.1 gives the details of the crystal and experimental data.

Figure. 4.1 represents the ORTEP (Oak Ridge Thermal Ellipsoid Plot)

diagram of the molecule with atom numbering with the unit cell projected

down the b-axis. There are two molecules of the title compound in the

asymmetric unit. The phthalate ion is getting attached to 4-Aminopyridine

molecules. Further, the analysis reveal that the title crystal belongs to

orthorhombic system with non-centrosymmetric space group P212121 and the

lattice parameters are a = 5.340 Å, b = 8.223 Å, c = 27.366 Å,

α = = = 90◦ and V = 1201.66 Å3.

24

Table 4.1: Crystal data and structure refinement for 4-APMP crystal

CRYSTAL DATA

Formula C13 H12 N2 O4

Formula weight [g / mol] 260.25

Crystal color, habit Pale yellow, Rod

Crystal system Orthorhombic

Crystal size [mm] 0.35 x 0.30 x 0.25 mm3

Space group P212121

Z 4, 1.439 Mg / m3

Unit cell parameters

a = 5.340 (10) Å b = 8.223 (2) Å c = 27.366 (8) Å α = 90º, = 90º, = 90º

Volume [Å3] 1201.66(5) A^3

F (000) 544

µ [mm-1] 1.064

DATA COLLECTION

Diffractometer ENRAF NONIUS CAD 4/MACH 3

Radiation MoKα

Wavelength [Å] 0.71073

Temperature [K] 293(2)

θ min ; θ max [º] 2.59 to 25.00 deg.

Total reflections measured 5415 / 2122

R int 0.0187

Range h = -6→6, k = -9→9, l = -32→31

REFINEMENT

Refinement method Full-matrix least squares

No. of reflection 5415

No. of parameters 185

Final R(F) [ I>2σ (I)] reflections 0.0308

w R [F2] 0.0740

Goodness-of-fit on F2 1.064

Absolute structure parameter 0.3 (11)

Δρ (min; max) [eÅ-3] -0.124 ; 0.154

25

4.2.2 FTIR Spectral Study

Fourier transform infrared spectrum (FTIR) of the 4-APMP crystal was

recorded in the range of 400-4000cm-1 using Perkin Paragon-500 through

KBr pellet technique and is shown in Figure. 4.2. A broad band at 3350 cm-1

is due to NH2 symmetric stretching. The peaks at 1928 and 955 cm-1 are

assigned to C-C-C ring breathing. The C – H in plane is found to be at 1157,

1026 and 620 cm-1. The peaks at 833 and 732 cm-1 is due to C – H out of

plane. All these assignments illustrate the presence of 4-Aminopyridinium

monophthalate and the assignments were shown in the Table 4.2.

Figure. 4.2: FTIR spectrum of the grown crystal

4.2.3 Optical Absorption Spectral Studies

An optical absorption spectrum of the grown crystal was carried out

between from 200 to 800 nm using VARIN CARY 5E UV-VIS-NIR

spectrophotometer and is shown in Figure. 4.3. The optical studies reveal

very low absorption in the entire visible region, which is one of the desired

properties for the device fabrication. The UV cut off wavelength of the crystal

26

was found to be around 335 nm. This very low absorption in the entire visible

region suggests its suitability for second harmonic generation.

Table. 4.2: FTIR analysis of the grown crystal

Wavenumbers (cm-1) Band Assignment

3350 NH2 Symmetric stretching

1928 C-C-C ring breathing

1644 C - C stretching

1371 C – NH2 stretching

1157 C – H in plane bending

1026 C – H in plane bending

955 C-C-C ring breathing

833 C – H out of plane

732 C – H out of plane

620 C – H in plane

27

Figure. 4.3: Optical absorption spectrum the grown crystal

4.2.4 Fluorescence Studies

The Fluorescence gives information about excitation of molecule

brought by absorption of photon. It may be expected in molecules that will be

aromatic or contain multiple conjugated double bonds with a high degree of

resonance stability. The emission spectrum of the grown single crystal of

4-Aminopyridinium monophthalate was recorded in the range of 350-600 nm

using Varian Carry Eclipse Fluorescence spectrometer and is shown in

Figure. 4.4. The sample was excited at 335 nm. The broad peak ranges from

400 to 600 nm with a maximum at 430 nm which indicates that 4-APMP

crystal has blue color of fluorescence emission.

28

Figure. 4.4: Emission Spectrum of 4-APMP crystal

4.2.5 Thermal analysis

The thermal stability of the title crystal was carried out by

thermogravimetric (TG) and differential thermal analysis (DTA) studies using

NETZSCH STA 409 C analyzer in the nitrogen atmosphere at the heating

rate of 10 ◦C/min in the temperature range between from 25 to 400 ºC and

the resultant thermogram is shown in the Figure. 4.5. The TGA curve shows

that there is a loss of weight in the range between 96 ◦C and 306 ◦C in

association with a sharp endothermic peak in DTA, which can be ascribed to

the absorption of energy for breaking of bonds at the initial stage of

decomposition. The TGA illustrates that there is no loss below 197.2 ºC,

thus assigned as the melting point of the crystal. From the results of DTA,

this is observed that there is no transformation inside the structure was

observed before melting point of 197.2◦C. Thus from the thermal studies, the

crystal can retain its texture up to 197.2º C, which proves its suitability for the

fabrication of nonlinear optical devices.

29

Figure. 4.5: TG/DTA spectrum of the title crystal

4.2.6 Microhardness studies

The mechanical hardness studies for the grown crystal were carried

out by a Leitz Wetzler Microhardness tester with a diamond pyramidal

indenter. The indentations were made using a Vickers pyramidal indenter for

various loads from 25 to 100g in the steps of 25g with a constant indentation

period of 25 s for all loads. Vicker’s hardness number (Hv) is calculated using

the relation

2

2

1.8544/

v

PH kg mm

d (4.1)

Where P is applied load in kg and d the diagonal length in mm. The variation

of Hv with applied load P is shown in Figure. 4.6. From the graph it becomes

clear that the hardness value increases with increasing load, thus satisfying

the normal indentation effect.

30

Figure. 4.6: Plot of load (P) vs. Hv

A plot of log p versus log d (Figure. 4.7) yields a straight line graph

and its slope gives the work hardening index n, and is found to be 4.89,

according to Meyer’s relation

1

nP K d (4.2)

Figure. 4.7: Plot of Log d vs. log P

31

Where K1 is the standard hardness value, which can be found out from the

plot of P versus dn (Figure. 4.8).

Figure. 4.8: Plot of dn vs. Load P

Since the material takes some time to revert to the elastic mode after

every indentation, a correction χ is applied to the d value and Kick’s law is

related as

2

2( )P K d x (4.3)

From Equations. (2) and (3), we get

1/2

/2 2 2

1 1

n K Kd d x

K K

(4.4)

The slope of dn/2 versus d yields (K2/K1)1/2 and the intercept is a

measure of χ and is shown in Figure. 4.10. The fracture toughness (Kc) is

given by

Kc = P/ c 3/2 (4.5)

32

Figure. 4.9: Plot of d vs. dn/2

Where C is the crack length measured from the centre of the

indentation mark to the crack tip, P is the applied load and geometrical

constant = 7 for Vicker’s indenter. The brittleness index (B) is given by

= Hv / Kc (4.6)

Yield strength σv of the material can be found out using the relation

2

12.5(2 )1 (2 )

2.9 1 (2 )

n

v

v

H nn

n

(4.7)

The stiffness constant gives an idea about the nature of

bonding between successive atoms. This property of the material by virtue of

which it can absorb maximum energy before the fracture occurs. For various

loads the stiffness constant is calculated using Wooster’s empirical relation

[89]

C11 = Hv7/4 (4.8)

33

Figure. 4.10: P vs σv

The variation of stiffness constant plotted with load is shown in Figure.

4.11. All the determined mechanical parameters are shown in the Table. 4.3.

Figure. 4.11: P vs C11

34

4.2.7 NLO studies

The powder SHG efficiency of the grown crystal was studied using

Q-switched Nd: YAG laser by employing the Kurtz and Perry powder

technique. The Nd: YAG laser emits fundamental wavelength of 1064 nm.

The output from Nd: YAG laser was used as source and it was illuminated to

the crystal powder. Pulse energy was 850 mj /second and pulse width was

about 9 ns, also repetition rate was 10 Hz. The SHG radiation at 532 nm

green light was obtained through photomultiplier tube. Hence the output

power of the grown crystal was 9.681 mj for the input power of 0.68 j, and the

powder SHG efficiency obtained is 1.1 times than that of well-known

reference material (KDP crystal).

Table 4.3: Microhardness value obtained on the 4-APMP Crystal

Hardness Parameters Values

n 4.89

K1 in kg/m 121.43

K2 in kg/m 48.86

Hp 64.9

Hv 28.25

Pm 100

Ps 25

Kc (MNm-3/2) 0.0282

(m-1/2) 10.017 x 102

σv (MPa) 929.32 x 102

C11 (Pa) 346.16

35

4.3 CONCLUSION

A novel nonlinear optical 4-Aminopyridinium monophthalate have

been grown by slow evaporation solution growth technique. The grown

crystal belongs to orthorhombic system. The presence of functional groups

was confirmed by FTIR analysis. The optical absorption studies reveal very

low absorption in the entire visible region. The title material has blue color

fluorescence emission at 430 nm. The thermal stability of the title compound

is found to be 197 °C. From Vickers hardness studies, work hardening

coefficient n is 4.89, thus confirms the exceptional hardness of the crystal.

Kurtz Perry powder method, used to confirm the SHG of the crystal, having

SHG efficiency 1.1 times that of KDP. All these studies confirm that the

grown crystal is the potential candidate for the fabrication of nonlinear optical

devices.

36

5. OPTICAL AND MECHANICAL STUDIES ON AMINO ACID DOPED

SODIUM ACID PHTHALATE (NaAP) SINGLE CRYSTALS

5.1 INTRODUCTION

Nonlinear optical materials have attracted many researchers due to its

potential applications in the field of photonics, lasers, electro - optic switches

and frequency conversion etc. [90-100]. During the past decade, number of

organic and inorganic materials with high nonlinear susceptibilities has been

synthesized. However, their device applications have been impeded by the

inadequate optical transmittance, poor optical quality and low laser damage

threshold [101]. The molecules in pure organic crystals are often bonded by

weak Vander Waals forces of hydrogen bonds, which result in poor

mechanical robustness. In the case of inorganic NLO materials, they have

excellent mechanical and thermal properties but relatively modest optical

susceptibilities due to the lack of π – electron delocalization [102-105, 42].

Phthalic acid family crystals are potential nonlinear optical materials and are

widely used in variety of applications [106]. Sodium acid phthalate is an

excellent material for SHG applications [107, 108]. In the present work,

attempts were made to grow amino acids (L-alanine, L-arginine, Glycine)

doped sodium acid phthalate by slow evaporation technique. Effect of

dopants is significant, because of the influence of doping on intrinsic defects

[109-114]. The results and characterization reveal that the presence of

dopants enhances optical, mechanical properties etc.

5.2 RESULTS AND DISCUSSION

5.2.1 Single crystal X-ray diffraction analysis

The amino acid doped sodium acid phthalate crystals were subjected

to single crystal X-ray diffraction analysis using by ENRAF NONIUS CAD4

single crystal X-ray diffractometer. The lattice parameters are measured and

are shown in Table 5.1. All the grown crystals belong to orthorhombic crystal

37

system having space group of B2ab which is in good agreement with that of

the literature [107, 108].

Table 5.1: Lattice parameters for Pure and doped crystals

compound

Name

Crystal

system

Space

group Unit cell parameters Volume

NaAP (pure) Orthorhombic B2ab a = 6.60 Å, b = 9.08 Å,

c = 25.84 Å, α = = = 90° V = 1548 Å3

NaAP + 1mole%

L-alanine Orthorhombic B2ab

a = 6.73 Å, b = 9.24 Å,

c = 26.25 Å, α = = = 90° V = 1631 Å3

NaAP + 3mole%

L-alanine Orthorhombic B2ab

a = 6.74 Å, b = 9.23 Å,

c = 26.28 Å, α = = = 90° V = 1635 Å3

NaAP + 5mole%

L-alanine Orthorhombic B2ab

a = 6.77 Å, b = 9.28 Å,

c = 26.35 Å, α = = = 90° V = 1655 Å3

NaAP + 1mole%

L-arginine Orthorhombic B2ab

a = 6.78 Å, b = 9.29 Å,

c = 26.38 Å, α = = = 90° V = 1661 Å3

NaAP + 3mole%

L-arginine Orthorhombic B2ab

a = 6.77 Å, b = 9.30 Å,

c = 26.39 Å, α = = = 90° V = 1662 Å3

NaAP + 5mole%

L-arginine Orthorhombic B2ab

a = 6.87 Å, b = 9.45 Å,

c = 26.76 Å, α = = = 90° V = 1737 Å3

NaAP + 1mole%

Glycine Orthorhombic B2ab

a = 6.68 Å, b = 9.19 Å,

c = 26.06 Å, α = = = 90° V = 1600 Å3

NaAP + 3mole%

Glycine Orthorhombic B2ab

a = 6.74 Å, b = 9.28 Å,

c = 26.29 Å, α = = = 90° V = 1644 Å3

NaAP + 5mole%

Glycine Orthorhombic B2ab

a = 6.81 Å, b = 9.38 Å,

c = 26.62 Å, α = = = 90° V = 1701 Å3

38

5.2.2 FTIR studies

The presence of functional groups and vibrational frequencies of pure

and doped NaAP single crystals identified by FTIR spectroscopy. The

recorded spectrum of the grown crystals were carried out between the range

400-4000 cm-1 using Perkin - Elmer spectrum one and is shown in Figures.

5.1- 5.3. An absorption band in the range 538-858 cm-1 appears due to C-H

out-of-plane deformations of the aromatic ring. The spectral band attributed

at 1118 cm-1 is due to C-H in-plane deformation of the aromatic ring. The

C-O stretching vibrations obtained as peak at 1354 cm-1. The peak at 1613

cm-1 assigned due to C-C skeletal aromatic ring vibrations. The carboxyl

group C=O vibrations appear near 1696 cm-1. All these assignments are in

very good agreement with NaAP crystals that of the reported values [108].

The L-alanine dopants assigned at 2867 cm-1 due to NH3+ asymmetric

stretching mode and 1468 cm-1 assigned for deprotonated carboxylic group

(COO-) characteristic absorption band. In the L-arginine dopants the peaks

at 3501 cm-1 NH2 asymmetric stretching vibrational mode, C-H stretching of

CH2 vibrations assigned at 2468 cm-1, the minute peak at 1466 cm-1 due to

NH2 symmetric bending mode.

And the Glycine dopants identified at 3161 cm-1 due to NH3+

Asymmetric stretching vibrational mode, C-O symmetric stretching mode

assigned at 1467 cm-1, and the peak at 1125 cm-1 for NH3+ rocking mode for

out plane bending respectively. From the above assignments verified that

amino acids were presence as dopants in NaAP single crystals.

39

Figure. 5.1: FTIR Spectra of L-alanine doped NaAP crystals

Figure. 5.2: FTIR Spectra of L-arginine doped NaAP crystals

40

Figure. 5.3: FTIR Spectra of Glycine doped NaAP crystals

5.2.3 UV-Vis-NIR spectral analysis

The UV-Vis-NIR spectrum of the grown crystals was recorded in the

range 300-800 nm using Perkin Elmer Lambda 35 UV-Vis spectrophotometer

and the resultant spectra is shown in Figures. 5.4, 5.5, and 5.6. The optical

absorption studies reveal that amino acids doped NaAP crystals show good

transparency in entire visible region and the UV cut off wavelength is found to

be around 313 nm, 320 nm and 317 nm for L-alanine, L-arginine and Glycine

doped NaAP crystals respectively. Moreover it is observed that the

absorbance decreases with increase in the doping concentration for all the

three dopants. This proves that the presence of dopants enhance the optical

property of the material. The very low absorbance in the entire visible region

suggests its suitability for the fabrication of optoelectronic devices [115].

41

Figure. 5.4: Absorption spectra of L-alanine doped NaAP crystals

Figure. 5.5: Absorption spectra of L-arginine doped NaAP crystals

42

Figure. 5.6: Absorption spectra of Glycine doped NaAP crystals

The optical absorption coefficient (α) was calculated from the

transmittance using the following relation,

1 1log

t T

(5.1)

Where T is transmittance and t is thickness of the crystal.

Owing to the direct band gap, the crystal under study has an

absorption coefficient (α) obeying the following relation for high photon

energies (hν); 1/2( )

gA h E

h

(5.2)

Where Eg is optical band gap of the crystal and A is a constant.

43

Figure. 5.7: Plot of (αhν) 2 vs. (hν) for pure and L-alanine

doped NaAP crystals

Figure. 5.8: Plot of (αhν) 2 vs. (hν) for pure and L-arginine

doped NaAP crystals

44

Figure. 5.9: Plot of (αhν) 2 vs. (hν) for pure and Glycine

doped NaAP crystals

The plot of variation of (αhν) 2 vs. hν is shown in Figures. 5.7, 5.8, 5.9.

Eg is evaluated by the extrapolation of the linear part and the band gap for

pure NaAP crystal is found to be 4.050 eV. But for L-alanine doped NaAP

the band gap values are 4.070, 4.075 and 4.077 eV respectively for 1mole%,

3mole%, 5mole% concentrations. Similarly, for L-arginine doped NaAP, Eg is

found to be 4.048, 4.051 and 4.052 eV respectively for 1mole%, 3mole%,

5mole% concentrations. Whereas for glycine doped NaAP the values are

4.054, 4.063 and 4.066 eV respectively for 1mole%, 3mole%, 5mole%

concentrations.

5.2.3.1 Determination of optical constants

The optical behaviour of materials is important to determine its usage

in optoelectronic devices. Knowledge of optical constants of a material such

as optical band gap and extinction coefficient is quite essential to examine

the material’s potential opto-electronic applications. Further, the optical

45

properties may also be closely related to the material’s atomic structure,

electronic band structure and electrical properties. The extinction coefficient

(K) for the grown crystals can be determined using formula

4K

(5.3)

The plot of K vs. photon energy (hν) is shown in the Figures. 5.10-

5.12. It is observed that the K decreases with increase in energy.

The reflectance (R) in terms of photon energy (Figures. 5.13-5.15) is

derived from the relation,

R (5.4)

Figure. 5.10: Extinction Coefficient of L-alanine doped NaAP crystals

46

Figure. 5.11: Extinction Coefficient of L-arginine doped NaAP crystals

Figure. 5.12: Extinction Coefficient of Glycine doped NaAP crystals

47

Figure. 5.13: Reflectance of L-alanine doped NaAP crystals

Figure. 5.14: Reflectance of L-arginine doped NaAP crystals

48

Figure. 5.15: Reflectance of Glycine doped NaAP crystals

The optical conductivity (σop) is a measure of the frequency response

of the material when irradiated with light (Figures. 5.16-5.18)

σop = (5.5)

Where c is the velocity of light.

Figure. 5.16: Optical Conductivity of L-alanine doped NaAP crystals

49

Figure. 5.17: Optical Conductivity of L-arginine doped NaAP crystals

Figure. 5.18: Optical Conductivity of Glycine doped NaAP crystals

Also, the electrical conductivity has been determined for the grown crystals

by optical method using the relation

σelec = 2λσop/α (5.6)

and the electrical conductivity is shown in Figures. 5. 19-5.21.

50

Firgure. 5.19: Electrical Conductivity of L-alanine doped NaAP crystals

Firgure. 5.20: Electrical Conductivity of L-arginine doped NaAP crystals

51

Firgure. 5.21: Electrical Conductivity of Glycine doped NaAP crystals

5.2.4 Microhardness measurements

The title crystals were carried out to Vickers microhardness tests using

Leitz Wetzler Microhardness tester with a diamond pyramidal indenter. A

diamond indenter was pressed the plane of pure and doped NaAP crystals

under the known load 25 –100g and the resulting indentation was measured.

The indentation time was 25s for all trials. The Vickers hardness number

was calculated using the relation

Hv = 1.8544 (P/d2) kg/mm2 (5.7)

Where P is the applied load in kg and d is the diagonal length of the

indentation impression mm2. The variation of it Hv when the applied load P is

shown in Figures. 5.22-5.24. The microhardness value is gradually increases

after load 50g which is lightly increased in the range of load from 25 to 100g

for different mole% of L-alanine doped NaAP crystals. The same results

were observed for different mole% of L-arginine and Glycine doped NaAP

52

crystals. Thus we can conclude that the presence of dopants increases the

hardness of the material.

Figure. 5.22: Hardness number of L-alanine doped NaAP crystals

Figure. 5.23: Hardness number of L-arginine doped NaAP crystals

53

Figure. 5.24: Hardness number of Glycine doped NaAP crystals

5.2.5 Nonlinear Optical studies

The second harmonic generation efficiency of pure and amino acid

doped sodium acid phthalate single crystals were studied using Q-switched

Nd: YAG laser by Kurtz powder test. The fundamental radiation of 1064 nm,

with pulse energy was 850 mj per second, pulse width of 9ns, and repetition

rate was 10Hz of infrared light beam focused on the powder samples of

amino acids doped NaAP crystals. The SHG efficiency of the doped crystal

is found to be lesser than that of KDP crystal. The relative SHG efficiency for

different doping concentration is shown in the Figure. 5.25.

54

Figure. 5.25: SHG efficiency of Doped amino acid crystals

5.3 CONCLUSION

Single crystals of amino acid doped sodium acid phthalate single

crystals were grown by slow evaporation solution growth technique at room

temperature. Single crystal X-ray diffraction analysis reveals that the title

crystals belong to orthorhombic system having space group B2ab. The

functional groups of the presence of dopants revealed with parent material.

The optical absorption spectra reveal that the amino acid dopants enhanced

the optical properties of the materials. The mechanical hardness study

reveals that the hardness increases with increase in the doping

concentration. The SHG efficiency is found to be lesser than that of KDP

crystal. All these studies confirm that the amino acid doped NaAP crystal

could be considered as a potential candidate for the fabrication of

optoelectronic devices.

55

6. STRUCTURAL, OPTICAL, MECHANICAL, THERMAL AND

FLUORESCENCE PROPERTIES OF NONLINEAR OPTICAL DIGLYCINE

BARIUM CHLORIDE MONOHYDRATE (DGBCM) SINGLE CRYSTAL

6.1 INTRODUCTION

The Nonlinear optical (NLO) materials have attracted many

researchers due to their wide applications in the area of photonics, lasers,

electro-optic switches and frequency conversion [116, 90-95]. In recent

years, complexes of amino acids with organic and inorganic acids possess

excellent nonlinear optical properties [61, 117-121]. Amino acids are

interesting materials for NLO applications, as this contains an asymmetric

carbon atom which makes them optically active and most of them crystallize

in non-centrosymmetric space groups. Also, amino acids exist as zwitterionic

nature, favours exceptional crystal hardness, making them ideal for the

fabrication of NLO devices [122, 123]. In addition, amino acid mixed

inorganic compounds are widely used in device fabrication because of their

high nonlinear optical coefficient and high degree of chemical inertness [124].

Hence in the present work, our aim is focused towards the growth of

Diglycine barium chloride monohydrate, a semi organic nonlinear optical

crystal, by slow evaporation solution growth technique. The grown crystals

were subjected to various characterisations and were discussed in detail.

6.2 RESULTS AND DISCUSSION

6.2.1 Single crystal X-ray diffraction analysis

The single crystal X – ray diffraction analysis for the grown crystals

was carried out using ENRAF NONIUS CAD-4 X-ray diffractometer to

determine the cell parameters. The results indicate the DGBCM

[Ba (NH2CH2COOH)2 Cl2. H2O] crystal belongs to orthorhombic crystal

system and space group Pbcn. The calculated unit cell parameter values are a = 8.26 Å, b = 9.29 Å, c = 14.82 Å, α = = = 90o and V = 1139 Å3. Which

are in very good agreement with that of the reported values [125-127].

56

The valence electron plasma energy, p is given by

2/1)(8.28 MZp (6.1)

Where Z = ((4 × ZC) + (12 × ZH) + (5 × ZO) + (1 × ZBa) + (2 × ZN) + (2 × ZCl)) =

58 is the total number of valence electrons, ρ is the density and M is the

molecular weight of the grown crystal. Explicitly p dependent Penn gap

and the Fermi energy [128], is given by

2/1)1(

p

pE

(6.2)

And

3/4)(2948.0 pFE (6.3)

Polarizability α obtained using the relation [129]

324

2

0

2

0

2

10396.0]3)(

)([ cm

M

ES

S

pp

p

(6.4)

Where, S0 is a constant for a particular material which is given by

2

0 ]4

[3

1]

4[1

F

p

F

p

E

E

E

ES (6.5)

The value of α so obtained agrees with that obtained using Clausius-

Mossotti equation which is given by,

)2

1(

4

3

aN

M (6.6)

All these calculated data for the grown crystal are shown in the Table 6.1.

57

Table 6.1: Some theoretical parameters on DGBCM crystals

6.2.2 FTIR studies

The FTIR study on the grown crystal was carried out between the

range 400 – 4000 cm-1 using Perkin-Elmer spectrum one and the resultant

spectrum is shown in the Figure. 6.1. The broadband around 3478 cm-1 is

due to NH asymmetric stretching. A peak at 2587 indicates the presence of

NH3+ stretching vibrations. The peaks at 1480 and 1111 cm-1 is due to the

NH3+ group of glycine molecule. The carboxylate group of the glycine

molecule is found to be around 671 and 1582 cm-1. The peaks at 896 and

1326 cm-1 are attributed to CCN and COO- stretching groups respectively.

All these assignments are in very good agreement with that of the reported

values [126, 127].

Parameters Values

Plasma energy (eV) 18.20

Penn gap energy (eV) 2.65

Fermi energy (eV) 14.11

Polarizability (cm3)

By Penn analysis 5.38 X 10-23

By Claussius- Mosotti equation 5.41 X 10-23

58

Figure. 6.1: FTIR spectrum of the grown crystal

6.2.3 Optical absorption studies

The optical absorption spectrum of the DGBCM crystals was recorded

in the range 200-1200 nm using Perkin Elmer Lambda 35 UV-Vis

spectrophotometer and is shown in Figure. 6.2. It is observed that the lower

cut off wavelength is around 240 nm and the crystal is found to be

transparent in the entire visible region, thus suggesting its suitability for the

fabrication of second harmonic generation devices. The optical absorption

coefficient (α) was calculated from the transmittance using the following

relation,

1 1log

t T

(6.7)

Where T is transmittance and t is thickness of the crystal.

59

Figure. 6.2: Optical absorption spectrum of the grown crystal

Owing to the direct band gap, the crystal under study has an

absorption coefficient (α) obeying the following relation for high photon

energies (hν); 1/2( )

gA h E

h

(6.8)

Where Eg is optical band gap of the crystal and A is a constant. The plot of

variation of (αhν) 2 vs. hν is shown in Figure. 6.3. Eg is evaluated by the

extrapolation of the linear part and the band gap is found to be 5.19 eV.

60

Figure. 6.3: Plot of (hν) vs. (αhν) 2

6.2.3.1 Determination of optical constants

The optical behaviour of materials is important to determine its usage

in optoelectronic devices. Knowledge of optical constants of a material such

as optical band gap and extinction coefficient is quite essential to examine

the material’s potential opto-electronic applications. Further, the optical

properties may also be closely related to the material’s atomic structure,

electronic band structure and electrical properties. The extinction coefficient

(K) for the grown crystals can be determined using formula [130, 131]

4K

(6.9)

The plot of K vs. photon energy (hν) is shown in the Figure. 6.4. It is

observed that the K decreases with increase in energy. The refractive index

(n) can be derived from the following relations,

61

2( 1) 3 10 3

2( 1)

R R Rn

R

(6.10)

Figure. 6.4: Plot of extinction coefficient (K) vs. photon energy (hν)

Figure. 6.5: Plot of photon energy (hν) vs. Refractive index (n)

62

The dependence of refractive index (n) as a function of photon energy

is shown in the Figure. 6.5. Initially, it is observed that the refractive index

decreases with increase in the photon energy. Later it becomes constant for

the all values of energy.

6.2.4 Microhardness studies

The microhardness of DGBCM crystal was carried out by a Leitz

Wetzler Microhardness tester with a diamond pyramidal indenter. The

indentations were made using a Vickers pyramidal indenter for various loads

from 25 to 100g in the steps of 25g with a constant indentation period of 25 s

for all loads. Vicker’s hardness number (Hv) were calculated using the

relation

2

2

1.8544/

v

PH kg mm

d (6.11)

Where P is applied load in kg and d is the diagonal length in mm. The

variation of Hv with applied load P is shown in Figure. 6.6. From the graph it

becomes clear that the hardness value increases with increasing load, thus

satisfying the normal indentation effect.

Figure. 6.6: Plot of P vs. Hv

63

A plot of log p versus log d (Figure. 6.7) yields a straight line graph

and its slope gives the work hardening index n, and is found to be 2.89,

according to Meyer’s relation

1

nP K d (6.12)

Where K1 is the standard hardness value, which can be found out from the

plot of P versus dn (Figure. 6.8). Since the material takes some time to revert

to the elastic mode after every indentation, a correction χ is applied to the d

value and Kick’s law is related as

2

2 ( )P K d x (6.13)

From Equations. (12) and (13), we get

1/2

/2 2 2

1 1

n K Kd d x

K K

(6.14)

Figure. 6.7: Plot of Log d vs. log P

64

Figure. 6.8: Plot of dn vs. Load P

The slope of dn/2 versus d yields (K2/K1)1/2 and the intercept is a

measure of χ and is shown in Figure. 6.9. The fracture toughness (Kc) is

given by

Kc = P/ c 3/2 (6.15)

Figure. 6.9: Plot of d vs. dn/2

65

Where C is the crack length measured from the centre of the indentation

mark to the crack tip, P is the applied load and geometrical constant = 7 for

Vicker’s indenter. The brittleness index (B) is given by

= Hv / Kc (6.16)

Yield strength σv of the material can be found out using the relation

2

12.5(2 )1 (2 )

2.9 1 (2 )

n

v

v

H nn

n

(6.17)

All the determined mechanical parameters are shown in the Table 6.2.

Table 6.2: Microhardness value obtained on the DGBCM Crystal

Hardness Parameters Values

n 2.89

K1 in kg/m 0.0319 x 10-2

K2 in kg/m 2.177 x 10-4

Hp 48.45

Hv 31

Pm 100

Ps 25

Kc (MNm-3/2) 0.013239

(m-1/2) 2.341 x 103

σv (MPa) 701.31

66

6.2.5 TGA/DTA studies

The thermal analysis was carried out for the grown crystals using by

NETZSCH STA 409C analyzer in nitrogen atmosphere at heating rate of

20 oC per minute from 25 oC to 400 oC and is shown in Figure. 6.10. From

DTA curve, the first endothermic peak at 171.7oC indicates the starting point

for the decomposition of the material, thus confirms that the materials can

retain its texture till 171.7oC. Another endothermic broad peak obtained at

312.6 oC illustrates the liberation of volatile substances like ammonia and

carbon dioxide in the compound. The TG analysis shows that the 34.9 % of

weight loss takes place during this transition. From the analysis, it is

observed that the material is stable up to 171.7˚C without any intermediate

loss.

Figure.6.10: TG/DTA analysis of the title crystal

6.2.6 Fluorescence studies

The Fluorescence spectrum was recorded to DGBCM crystal sample

using Varian Cary Eclipse Fluorescence spectrometer at room temperature.

The sample was excited at 240 nm and the spectra was recorded in the

67

range from 200 to 700 nm is shown in Figure. 6.11. A high intense peaks at

418 nm and 489 nm are observed and shows that DGBCM exhibits blue and

bluish green fluorescence. Either different low intensity peaks can be

intrinsic defects of crystal.

Figure. 6.11: Fluorescence spectrum of the DGBCM crystal

6.2.7 Second harmonic generation study

The second harmonic generation efficiency (SHG) was determined for

the DGBCM crystal using a Q-switched high energy Nd: YAG laser emitting

1064 nm radiation. The emission of green radiation by the sample was

confirmed and the SHG efficiency of DGBCM is 2.18 times more than that of

the KDP single crystal. The comparative SHG efficiencies of some semi

organic crystals relative to KDP are shown in Table. 6.3. [132].

68

Table. 6.3: Comparative of SHG efficiencies of NLO crystals relative to KDP

Name of the samples SHG efficiency

KDP 1.0

-glycine

L – Tyrosine Hydrochloride

L – Alanine Lithium Chloride

L – Alanine Acetate

L – Alanine Chloride

L – Alanine Bromide

Bis thiourea Lithium chloride

Bis thiourea cadmium zinc chloride

1.5

0.15

0.43

0.30

0.20

0.30

0.90

1.10

Diglycine barium chloride Monohydrate*

(Current Study) 2.18

6.3 CONCLUSION

Single crystal of Diglycine barium chloride monohydrate, a semi

organic NLO material, has been grown by slow evaporation solution growth

technique. The single XRD analysis confirmed that the grown crystals

belong to orthorhombic system having space group Pbcn. FT-IR analysis

confirms the presence of all the functional groups in the crystal lattice. The

optical absorption spectrum reveals that the crystal has good optical

transmittance in the visible IR region, also has high optical band gap energy.

Micro hardness test reveals that the material has good mechanical stability

and good yield strength. The thermogravimetric (TGA) and differential

thermal analysis (DTA) reveals that the material has high thermal stability.

The fluorescence spectrum shows that the grown crystals emit blue

fluorescence. The nonlinear optical study confirms that the SHG efficiency of

DGBCM is 2.18 times higher than KDP crystals. All these studies confirm

that the diglycine barium chloride monohydrate, a semiorganic nonlinear

optical material, is a potential candidate for the fabrication of nonlinear optical

devices.

69

7. CONCLUSION

The summary of the results of the present study and conclusions

drawn are presented below.

A novel NLO 4-aminopyridinium monophthalate crystal was grown by

the slow evaporation solution growth technique. The grown crystal belongs

to the orthorhombic system. The presence of functional groups was

confirmed by FTIR analysis. The optical absorption studies revealed very

low absorption over the entire visible region. The title material had a blue

fluorescence emission at 430 nm. The thermal stability of the title compound

was found to be 197 ◦C. From Vickers hardness studies, the work hardening

coefficient n was found to be 4.89, thus confirming the exceptional hardness

of the crystal. The Kurtz Perry powder method was used to confirm the SHG

behaviour of the crystal, and SHG efficiency was found to be 1.1 times that of

KDP. All of these studies confirmed that the grown crystal is a promising

candidate for the fabrication of NLO devices.

Amino acid-doped NaAP single crystals were grown by slow

evaporation solution growth at room temperature. Single crystal X-ray

diffraction analysis revealed that the title crystals belonged to the

orthorhombic system with space group B2ab. The presence of functional

groups was determined qualitatively using FTIR analysis. The optical

absorption spectra revealed that the amino acid dopants enhanced the

optical properties of the materials. The mechanical hardness study revealed

that the hardness increased with increasing doping concentrations. The

SHG efficiency was compared with that of KDP. All of these studies

confirmed that the amino acid-doped NaAP crystal could be considered a

promising candidate for the fabrication of optoelectronic devices.

Single crystal diglycine barium chloride monohydrate, a semiorganic

NLO material, was grown by the slow evaporation solution growth technique.

The single crystal XRD analysis confirmed that the grown crystals belonged

to the orthorhombic system with space group Pbcn. FTIR analysis confirmed

70

the presence of all of the functional groups in the crystal lattice. The optical

absorption spectrum revealed that the crystal had good optical transmittance

in the visible IR region as well as a high optical band gap energy.

Microhardness tests revealed that the material had good mechanical stability

and good yield strength. The thermogravimetric (TGA) and differential

thermal analyses (DTA) revealed that the material had high thermal stability.

The fluorescence spectrum showed that the grown crystals emitted bluish-

green fluorescence. The NLO study confirmed that the SHG efficiency of

DGBCM was 2.18 times higher than that of KDP. All of these studies

confirmed that diglycine barium chloride monohydrate, a semiorganic NLO

material, is a promising candidate for the fabrication of NLO devices.

71

8. SCOPE OF FURTHER WORK

In the future, attempts will be made to grow bulk single crystals (4-

APMP, SAP and DGBCM) along their growth axes to investigate their

growth rate, transparency and nonlinear optical properties such as

nonlinear coefficients, threshold frequency, phase matching behaviour,

other higher harmonic generations and ferroelectric hysteresis studies,

etc.

A systematic study on solution pH will shed more light on the habit

morphology, growth rate and physical properties.

Additionally, attempts can be made to grow application oriented crystals

using the Sankaranarayanan – Ramasamy (SR) method.

Advanced microscopic techniques, such as AFM and TEM, can be used

to characterize the grown samples.

The etching behaviour on the growth planes can be done using various

organic solvents to estimate the dislocation density and lattice

inhomogeneity and to identify the growth mechanism.

119

TECHNICAL BIOGRAPHY

Mr. G. Marudhu (RRN. 1090206) was born on 6th March 1983, in

Vandavasi, Tamil Nadu. He completed his schooling in Govt. Higher

Secondary School at Vandavasi. He received his B.Sc. degree in Physics

from Govt. Arts College at Cheyyar, University of Madras in 2003. He

completed his M.Sc. in Physics at A.V.V.M. Sri Pushpam College at Poondi,

Thanjavur, Barathidasan University in 2007. He completed his B.Ed. degree

in Physical Science from Paulson’s Teacher Training College at

Pulichapallam, Vanur, Thiruvalluvar University in 2008. He received his

M.Phil. degree in Physics from A.V.V.M. Sri Pushpam College at Poondi,

Thanjavur, Barathidasan University in 2009. He has six years of experience

in the teaching field. Currently, he is working as an assistant professor in Sri

Ramanujar Engineering College at Chennai. He is pursuing his Ph.D. in

Physics in the Department of Physics in B.S. Abdur Rahman University at

Chennai. His research area is “growth and characterization of NLO crystals

for optoelectronic device applications.” He has published two papers in peer-

reviewed international journals and has presented three papers at national

conferences. His e-mail address is marudhu.g@gmail.com, and his contact

number is 9566751751.