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Photoluminescence and PhotocatalyticPhotoluminescence and Photocatalytic

studies of doped and capped ZnO andstudies of doped and capped ZnO and

CeOCeO22 nanomaterialsnanomaterials

Ph.D

Proposal

By

Manish Mittal

Roll No. 950912008

Under the Supervision of

Dr. O.P Pandey

Professor

School of Physics and Materials Science

THAPAR UNIVERSITY, PATIALA(PUNJAB)-147004



PRESENTATION OUTLINE

Nanotechnology

Need of capping

Literature review

Gaps

Objective

Methodology

Experimental work done so far Results and Discussion

References



Nanotechnology

Deals with various structures of matter having dimensions of the order of a billionth of a meter.

Different types of nanostructures compared with bulk



Band Gap comparisonWhen the radius of nanoparticle approaches the size of the exciton Bohr radius,the motionof electrons and holes become confined in the nanoparticle. A created electron-hole pair can only fit into the nanoparticle when the charge carriers are in the state of higher energy.As a result the band-gap increases with decreasing particle size.

Here the kinetic energy becomes quantized and the energy bands will split into discrete

levels and phenomena is known as quantum size effect. These structures have very highsurface to volume ratio & hence surface defects play an important role in their study.



Quantum confinement effects

It is possible to engineer the electronic structure of a material,

by reducing the crystal size.

Quantum confinement effects are observed when the nano-

crystallite size is less than the exciton Bohr radius

nanocrytal bulk g g bulk g l nanocrysta g MR

E E E E 2

22

)()()( 2

TJ!(!



What extraordinary at nano-scale?

Physical, Chemical, Biological .........propertiesdrastically change

Why????

* Surface to volume ratio increases

* Confinement of electron-hole pairs



Need for Capping

Surface passivation

Control agglomeration



Various Techniques for the

preperation of nanoparticles

1. Thermal Decomposition Method

2. Chemical Vapor Deposition Method

3. Sol-Gel Method

4. Spray Pyrolysis Method

5. Co-Precipitation Method



Advantages of Co-Precipitation Method

1. Simple growth process for large scale production

2. Efficient

3. Inexpensive

4. Homogeneous distribution of doped ions in the

host matrix



Scientist Name/Year/Sample/Route Work Done Gaps

Reddy et al.(2011)/ ZnO:Cu/Wet

chemical method(1)

XRD shows 40nm of undoped

and37nm for Cu doped ZnO

nanoparticles having wurtzite

structure. PL studies shows decrease

in green emission and increase of UVemission due to decrease in

defects.TEM shows 40-50nmof

particle size.

Concentration of defects responsible

for deep level emission could be

reduced with Cu doping and it is

possible to tune UV emission but the

percentage of dopant required for defect reduction is not reported.

Chauhan et al. (2010)/ZnO:Cu/Co-

Precipitation /(2)

XRD shows increase in particle size

with doping than undoped ZnO NPs.

However, the particle size reduceswith increase in dopant concentration

but still greater than undoped ZnO

NPs. UV shows decrease in band gap

from 3.15-2.92eV of undoped and Cu

doped ZnO.

Reddy et al.(1) reported decreaes in

particle with doping but here the

particle size increase with doping.

Literature Review«



Literature Review«


Rana et al. (2010)/ZnO:Cu/ Wet

chemical /(3)

XRD results shows decreaes in

particle with doping than undoped

ZnO NPs. SEM and EDS shows

single phase NPS of doped and

undoped ZnO and no other element

except Zn and O respectively.

Here again the decrease in particle

size is reported with doping which is

contradictory to as reported by Reddy

et al.

PL and UV-vis spectra is not done.

Ullah et al. (2007)/ ZnO: Mn/Wetchemical/(13)

Showed that Mn doped ZnO bleachesMB much faster than undoped ZnO

upon its exposure to UV light.

The doping concentration proposed to be 1% for faster degradation of MB.

Different dopant concentrations were

not tried.



Literature Review«


Tsuzuki et al.(2009)/ZnO:Mn/Sol-

gel/(14)

XRD shows 10nm particle size. UV

is done. 3% Mn doping of 3% is

reported for photocatalytic

degradation of Rh-B dye.

Variation in dopant concentration is

required for getting optimum dopant

conc. For degradation of dye.

Singh et al.(2009)/Capped

ZnO/Chemical method(6)

XRD- 12-20nm Paricle size.TG has

been found to be more efficientcapping agent than TEA(

triethnolamine) , and Oleic acid.

Variation in concentration of capping

agent is required to study their effectson PL. Energy transfer mechanism is

required for tunable emission.



Sample and

Synthesis route

Dopants

and

Concentra

tion

Excitation Emission UV(Band

Gap)(eV)

XRD &

ParticleSize

TEM Remarks

CeO2

[20]

(2010) (microwave)

-------------

---

---------- --------- 3.1 Cubic

9nm

10nm SEM and Propylene glycol

usedas stabilizing agent

CeO2

[21] (2001)

Combustion

Er ----------- 550nm

(Green)&

660nm

(Red)

------ 18,38 &

70nm

Dark and White

clouds appeard.

Dark clouds are

crystallne & white

are amorphous.

18nm are more

amorphous than

38nm.

PAS is done.

CeO2

[22] (2002)

Soft solution chemical

Calcia

20mol%

----------- --------- 300(Trans

mittance)

Fluorite 50nm(Pure),

5-10nm

(doped)

pH-7,11 Doping CaO with

CeO2 reduce the particle

size and increase UV

shielding and transparency

to visible light.

Comprehensive Study of Literature



Sample and Synthesis

route

Dopants

and

Concentrat

ion


Gap)(eV)

XRD &

Particle Size

(nm)

TEM Remarks

CeO2

[6]

(2002)

Chemical Precipitation

------------ ------------ ----------- 3.15 Calculated

Lattice

parameter

from (h,k,l)

6nm and bigger Lattice parameters increases

upto 0.45% as particle size

reduces to 6nm.

CeO2

[9]

(2006)

Co-precipitation method

Ca(10,20,3

0,

40& 50%)

315nm

( pure),

250-330nm

(doped)

-------- 3.20

( pure),3.36

& 3.51

(doped)

Fluorite type

cubic

9.3nm( pure),

5.7nm

(50%doped)

8.3nm( pure) 5.9 &

6.3nm(20 & 50%

doped)

Above30mol% Ca doping,

sample contain CaCo3-

secondary phase and is not

suitable for cosmetic

products.

CeO2

[23]

(2006)

Sol-Gel

PtAu

(Bimetallic

catalyst),Pt & Au

--------- -------- ------- CeO2-16.18,

1%PtAu-

15.14,0.5% PtAu-

30.77,

2%Pt-13.65,

1%Pt-13.65,

1%Au-13.64

5-10nm Catalytic studies are done

with PtAu, Pt & Au doped

CeO2



Sample and

Synthesis route

Dopants and

Concentration


Gap)(eV)

XRD&

Particle Size

(nm)

TEM Remarks

CeO2

[24]

(2006)

Soft solution

chemical

Calcia doped

silica coated

---------- --------- 300(Trans

mittance)

----------- 10-15nm

Calcia doped

Non coated calcia doped

ceria shows better UV

shielding ability and

transparency to visible light

region than calcia doped

coated ceria

CeO2

[13]

(2006)

Composite-

hydroxide-mediated

------------- -------------- -------- ----- Cubic lattice

constant-

5.411A0

2-3nm at

1650C(0h),5-7nm at

1900C(48h),

2-4nm at 2200C (0h)

and 6-8nm at 2200C

(120h)

The ceria particle with sizeless than 6nm display a very

strong agglomeration to

minimize the interface

energy.

CeO2

[31]

(2007)

Hydrothermal

Synthesis

--------- ---------- -------- ------ Cubic

15.5nm

5-6nm

(cerium hydroxide),

10-15nm

(Cerium acetate)

Study Lattice type and lattice

constant at 500 and 10000C.



Sample and

Synthesis route

Dopants and

Concentration


Gap)(eV)

XRD &

Particle Size

(nm)

TEM Remarks

CeO2

[20]

(2008) Precursor

growth calcinations

Sm3+ 369nm Two

bands

325-

430nm &

260-

290nm

------ Fluorite

Small particle

size

----------- Rod like structure without

PVP and spherical particles

100nm size with PVP

reported by SEM

CeO2

[22]

(2009)

Silver (0.1,

0.25, 0.5, 0.75

& 1.0mol %)

---------- ------- ------- Cubic 5-6nm

( pure CeO2), 7-8nm

(Doped CeO2)

SEM and EDS studies

CeO2

[32]

(2009)

Homogeneous

Precipitation

----------- ------ --------- ------- Cubic

13-20nm

------------ Study the variation of particle

size with temp.

CeO2

[27]

(2010) precipitation

method

Fe(0,10,40,50,6

0,90,100%)--------- --------- 342

(3.62)

Concludes the

formation of

mixed oxides

10-20nm Degrade dyes like MB & CR.

Max. Degradation is at 50%

of Fe.



Sample and

Synthesis route

Dopants and

Concentratio

n


Gap)(eV)

XRD &

Particle Size

(nm)

TEM Remarks

ZnO

[14] (2006)

Precipitation method

Eu and Eu-Li

codoped

--------- ------ ------- ---------- --------- Particle size of 40nm has

been observed with SEM.

Cathodolumine-scence

spectra

ZnO

[18]

(2008) Chemical

------------- 300-320nm 410&558n

m

262nm Hexagonal

wurtzite

1-3nm Green emission is observed

due to singly ionized oxygen

vacancy.

ZnO

[1

9](2008) Co-

Precipitation

Mn & Cu --------- --------- 3.2 -------- 3-5nm Mn ions affect the absorption

characteristics more than Cuions.

ZnO

[23]

(2009) Wet Chemical

Mn --------- --------- 3.2 ----------- 3-5nm Photocatalytic activity of

doped ZnO is more than pure

ZnO



Sample and

Synthesis route

Dopants and

Concentration


Gap)(eV)

XRD &

Particle Size

(nm)

TEM Remarks

ZnO

[31]

(2010) Sol-Gel

Vanadium 325nm &

371nm

-- -- Wurtzite

Zn3(VO4)2

and Zn2V2O7

phases also

appeared, 14-

20nm

15-20nm Defect produced due to

doping of vanadium element

improve the photocatalytic

activity which can further

improve by varing doping

concentration.

ZnO

[33]

(2010) Sol-Gel

Eu, 1,2,3% 320nm -- -- Hexagonal

wurtzite

structure

--- Optical properties can be

significantly improved by Eu

doping.UV emission is

greatly reduced at 3% doping

conc.

ZnO

[34]

(2010) Sol-Gel

Cs -- -- 3.263 Wurtzite --

ZnO

[36]

(2010) Co-

Precipitatio n

Silver (0,1,2,3,4

and 5%)

-------- ------- 3.3 Hexagonal,wu

rtzite,27-

38nm

-------- Temperature variation

300-8000C



Sample and

Synthesis route

Dopants and

Concentration


Gap)(eV)

XRD &

Particle Size

(nm)

TEM Remarks

ZnO

[36]

(2011)

Co-Precipitation

Ni(0,1,2,3,4,5

%)

--------- ---------- (Undoped)

300-3.35

400-3.05

500-3.00

800-2.90

(Doped)

300-3.2

400-2.95

500-2.90

800-2.85

Wurtzite

28-37nm

(8000C),

30-42nm

(10000C)

------- The band gap value of

prepared undoped and Ni

doped ZnO Nps reduced as

annealing temp.increased upto

8000C



Doped and undoped ZnO nanoparticles have been studied for their photoluminescence and photocatalytic applications but capping withemissive polymers like PVP, Thioglycerol, Chitosen etc. on surfacealong with different dopants is not done in detail.

Capping emissive polymers results in tunable emission but their effecton ZnO and doped ZnO nanoparticles is required for their possible useas optoelectronic materials.

From literature survey of doped CeO2 nanoparticles, it appears dopedCeO2 systems have been investigated but the doping effect in ceriananoparticles with well characterized size is not done previously. Thedoping of ceria at that small size can be very beneficial to further improve its catalytic properties.

Doping with various dopants (Ag, Ca, Er, Fe, Pt, Au, CaO, Sm etc.) in

CeO2 has been done but their photocatalytic studies are not available indetail. In some cases dopants concentration increase and sometimes theyreduce the photocatalytic activities. When dopants changes Ce4+ to Ce3+

they are useful for the UV filteration and if they are not transformingCe4+ to Ce3+ then they can be used for degradation of dye. So detailedstudy is needed on the dopant concentration required for UV filterationand degradation of dye.

Gaps in present study



1. To synthesize Mn and Cu doped and capped ZnO nanomaterials by chemical

pr ecipitation route.

2. To study the effect of capping agents like PVP and Chitosen on UV and PL

properties.

3. To synthesize Ca and Er doped and undoped CeO2 nanomaterials.4. To study effect of dopants on conversion of Ce4+ to Ce3+ which results in

shifting of catalytic properties useful in UV filtration applications.

5. To study their photocatalytic and photoluminescence properties using UV-

visible, PLE and PL spectroscopy.

6. To study morphological studies for structural and size measurement using

XRD, SEM, TEM etc.

Objectives



ZnO and CeO2 nanostructures will be fabricated using chemical routes.

ZnO will be doped with Mn and Cu whereas CeO2 will be doped with Caand Er respectively.

Capping agents like PVP, Merceptoethanol, Thioglycerol, Chitosen etc.

will be tried to passivate the surface. ZnO and CeO2 nanostructures will be characterized by using XRD, TEM,

SAED, Photoluminescence spectroscopy, UV- visible absorption andreflectance spectroscopy, EDS etc.

«Methodology«



ZnO nanoparticles wer e synthesized by chemical pr ecipitation

technique by adding appropriate amount of zinc acetate and sodium

hydroxide.

0.5 M Zinc acetate sol. In aqueous medium wer e added in 1%

Thioglycerol(TG) and then 0.5 M sodium hydroxide was added dropwise and stirr ed continuously.

The pr ecipitate soon appears after the addition of sodium hydroxide

and they wer e filter ed using Whatman 40 filter paper .

The particles wer e washed several time with ethanol and wer e dried

at 3000C in vacuum.

«Work Done«.



Characterization

Homogeneous sol.

Capped ZnO nanoparticles

OpticalMorphological

Autoclave

FLOW CHARTWork Done«

Zinc acetate Mixing Capping agent

NaOH

Magnetic stirring

Colloidal Sol.Washing, Filtration ,

Vacuum oven drying



Results and Discussion

MorphologicalCharacterization and Nano-size confirmation

XRD pattern of and uncapped (a) and (b)TG capped

ZnO nanoparticles

For XRD Rigaku, model D±

maxIIIC diffractometer with

Cu K radiation is used.

Using Scherrer formula

d =0.89 / cos

Average crystallite size of

~13nm and ~16nm for capped

and uncapped ZnO

nanoparticles is obtainedhaving hexagonal wurtzite

structure.

30 40 50 60 70 80

0

500

1000

1500

2000

C o u n t s

Angle(2 U)

Uncapped ZnO NPs

TG capped ZnO NPs

100

002

101

102

110

103

200

112

201

Wurtzite ZnO

(a)



Excitation spectra of synthesized capped and uncapped

ZnO nanoparticles

Steady state PL spectra recorded using FlouroMax-3 (Jobin-Yvon)spectroflourometer

280 300 320 340 360 380

345nm

Capped ZnO 345nm

Wavelength(nm)

uncapped ZnO

I

n

t e

n

s i t y ( a . u

.

)

Excitation spectra at 460nm emission

Excitation spectra Shows excitonic peak

at 345nm for both capped and uncapped

ZnO Nps.Which is blue shifted than

bulk ZnO which comes at 380nm.



SEM Analysis of TG capped ZnO

clearly shows the formation of

ZnO Nps

EDX spectrum shows the pr esence of zinc and oxygen ions in larger

amount along with carbon and

nitrogen in less amount which is due

surface adsorbed polymer TG.

SEM and EDX analysis of capped ZnO nanoparticles



Element Wt. % At%At.At. %

%

CK 13.03 29.90

NK 01.02 02.01

OK 24.45 42.14

ZnK 61.50 25.94

Table I- EDX analysis of TG capped ZnO NPs



Applications

Since common cells are almost transparent, they can hardly be seen by human eyes

under optical microscope. Researchers often rely on certain fluorescence material, whichattach to the interested biological component, in order to detect cell activities. Althoughorganic fluorescent dye has been widely used to label the cells, their drawbacks, such asnarrow absorption band and high chemical reactivity, are obvious compared to thenanomaterial counterparts, quantum dots (QDs), especially ZnSe, CdSe, ZnS:Mn whoseemission spectra spread most of the visible wavelengths.

Both biocompatibility and aqueous solubility are required for QDs to be used inbiological system. Because CdSe QDs synthesized through metal-organic approach are

hydrophobic, ligands exchange or extra coating are needed for those dots to use inaqueous environment. In addition, highly toxic metalorganic precursors make thiscomplex process much less desirable than the method under development here are,which offers an easy and user-friendly way to prepare high quality CdSeQDs. ZnSe/ZnScore/shell structure QDs can be synthesized to significantly enhance the PL intensityfrom ZnSe so that much less QDs are needed to inject into cells to obtain strong signals.

Silica coatings were also developed on the core/shellQDs to increase chemical stabilityand biocompatibility of the QDs. Silica coatings are also easy to functionalize byconjugating with various molecules, which can be used to track the cell activities orchemical pathways inside cells. It has been reported that PL intensity and peak wavelength of the QDs could change upon chemical bonding events of the functionalmolecules. The electric charges change, among others, is considered to contribute to thisprocess. Therefore, the effect of an applied electric field, known as Stark effect, on thePL intensity and wavelength of the QDs was studied to give preliminary understandingof such phenomenon.



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Valance Band

Zni

+0.4eV

VZn-

0.61eV0.4eV

527nm486nm418nm400nmBand edge

emission

3.3-3.5eV

Conduction Band

VZn

Exciton Transitions in Cu Doped ZnO nanoparticles

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