Research Article Enhancement of UV Excited...

Research ArticleEnhancement of UV Excited Photoluminescence byFabry-Perot Microcavity

Chunxian Tao1 Jun Ruan1 Dong Liang2 Zhaoxia Han1 Liang He1 Ruijin Hong1

Xiao Cui1 and Dawei Zhang1

1Engineering Research Center of Optical Instrument and System Ministry of Education and Shanghai Key Lab ofModern Optical System University of Shanghai for Science and Technology No 516 Jungong Road Shanghai 200093 China2College of Communication and Art Design University of Shanghai for Science and Technology No 516 Jungong RoadShanghai 200093 China

Correspondence should be addressed to Chunxian Tao taoussteducn

Received 22 July 2015 Revised 20 November 2015 Accepted 26 November 2015

Academic Editor Khalique Ahmed

Copyright copy 2015 Chunxian Tao et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

A light-emitting microcavity with the structure of dielectric mirrorphosphor coatingdielectric mirror for the enhancement ofPL efficiency excited under UV light was designed and fabricated The fluorescence emission of Lumogen S0795 coating withinmicrocavity structure is significantly enhanced compared with the coating on bare substrate The measurement results indicate thepossibility of developing front illuminated CCD based on optical resonant cavity for UV-visible imaging with higher sensitivity

1 Introduction

One-dimensional photonic crystal is a periodic structurethat consisted with different refractive index of dielectricmaterials [1 2] When the light comes through this mediumthe light of certain frequency range will be suppressed andformed into photonic band gap It is similar to the bandstructure of the electrons in semiconductor material Thetheoretical model [3] and the application of photonic crystalsare very extensive [4 5] and the most common and easiestpreparation of one-dimensional photonic crystal is usuallyprepared by physical vapor deposition method of multilayerstructure with defect whichmeans a Fabry-Perot cavity sizedfor a light wave on the one-dimensional direction verticalcavity surface

In recent years because the significance on basic physicalelectrodynamics research the research on emission proper-ties of any kinds of luminous materials in microcavity hasbeen paid more and more attentions [6ndash8] Particularly theplane microcavity made of organic materials has been moreconspicuous [9ndash11] Lumogen a kind of organic fluorescentmaterial with UV-frequency conversion ability can be usedin CCD device to detect the ultraviolet spectrum area Inthis paper we adopted Lumogen as photonic crystal defect

area Based on the characteristics of stimulated emissionof the Lumogen material we design an artificial crystalstructure in the form of Fabry-Perot microcavity to improvethe photoluminescence efficiency of the fluorescent materialwhich makes CCD device have a greatly improvement indetective ability and sensitivity to ultraviolet signal

2 Simulation

When we come up with the traditional multilayer highreflective film there only exists light cut-off region in thecenter frequency which is represented by 120596

0and its odd

number of times and there is no light cut-off region at theincident for 120596

0even times as shown in Figure 1 From the

perspective of photonic crystals there are band gap structuresin general frequency 120596

0integer times Namely when 119896 lowast

119889 = 119899 lowast 120587 there exists a band gap If the light comesthrough a vertical incidence from medium A to medium Bthe reflectivity can be given by Fresnel formula

119877 = 119903119886119887119903lowast

119886119887

119903119886119887=

119899119887minus 119899119886

119899119887+ 119899119886

(1)

Hindawi Publishing CorporationJournal of SpectroscopyVolume 2015 Article ID 153483 6 pageshttpdxdoiorg1011552015153483

2 Journal of Spectroscopy

0

20

40

60

80

100

1205961205960

05 10 15 20 25 30 35

Tran

smitt

ance

()

Figure 1 Transmission spectrum of one-dimensional photoniccrystal at 0∘ incidence

300 400 500 600 700 800 900

0102030405060708090

100

57

911

Refle

ctan

ce (

)

Wavelength (nm)

Figure 2 Reflective spectrum of 5 7 9 and 11 periodic dielectricmultilayer

where 119899119886and 119899

119887are the refractive indexes of two different

media For the limited periodic structure material we coulduse the transfermatrixmethod to get the transfer characteris-tic of themembrane reactor By the above theory the reflectivespectra of the films with period of 5 7 9 and 11 respectivelycan be obtained as shown in Figure 2The period mentionedhere refers to a pair of membrane consisting of two differentmediums A and B Theoretically the photonic crystal shouldhave infinite structure but in practice thewidth of the energygap basically no longer changes as long as there is a certainnumber of periods as shown in Figure 2 So the traditionalhigh antimembrane can be regarded as a kind of one-dimensional photonic crystal and the finite membrane stackshould also be considered a special case of one-dimensionalphotonic crystal So the research of fluorescent materialenhancement can be discussed combined with thin solid filmoptical theory with the theory of the photonic crystal

When the fluorescent material is doped in photoniccrystal an impurities defect mode in the photonic band gap

Reflector A Reflector B SubstrateFluorescentmaterial

Figure 3 Structure design of one-dimensional photonic crystal

would be created It would change the light propagationmodeand the density of states The enhancement ratio can beobtained by comparing the density of states in free space andphotonic crystal According to the gold Fermirsquos rule the ratioof spontaneous emission in photonic crystal and free spacewas decided by the ratio of the density of states The densityof states in free space was given by

120588119894(120596) =

1

119881

sdot

119889119873

119889119881

=

1205962

12058721198623=

4119899

119888

(2)

where 119899 was the refractive index of medium 119888 was thespeed of light in vacuum and 119881 was the mode volume 119862 isassociated with parameters and frequency of the dipole of theincident photonThe density of states in photonic crystal wasgiven by

120588119888 (120596) =

1

120575120596119881

=

119899

119888

sdot radic10119865 119865 =

4119877

(1 minus 119877)2 (3)

where 119865 was the degree coefficient and 119877 was the reflectivityof the mirror There is only single mode where bandwidth is120575120596 and the frequency is 120596 So the ratio of the statersquos densityof photonic crystal and free space that was represented by119872was given by

119872 =

radic40119877

4 (1 minus 119877)

(4)

So the value of119872 was decided by the reflectance 119877 and isgreater than 1 in the case of119877 gt 90Thatmeant the photoniccrystal can improve the rate of spontaneous emission andone dimensional photonic crystal structure can effectivelyenhance the luminous efficiency of organic light-emittingmaterials

As shown in Figure 3 there was a fluorescent layer asdefect in our designed photonic crystal structure In order tomake the UV detecting light incentive fluorescent materialthe reflective mirror A was designed that the UV band lightcould pass through and a certain band gap with the centerwavelength of 525 nmWhile the reflective mirror B was onlydesigned with a band gap of certain bandwidth in the centerof 525 nm So this was a photonic crystal with asymmetric

Journal of Spectroscopy 3

350 400 450 500 550 600 650 700 750 800

0102030405060708090

100

Tran

smitt

ance

()

Wavelength (nm)

34

56

Figure 4 Transmitted spectrum of one-dimensional photoniccrystal with different periods

350 400 450 500 550 600 650 700 750 8000

102030405060708090

100

Tran

smitt

ance

()

Wavelength (nm)

140nm130nm

120nm110nm100nm

Figure 5 Transmitted spectrum of one-dimensional photoniccrystal with different thickness of defect layer

structure According to the characteristics of photoniccrystal the transmission spectrum was very sensitive to theinfluence that geometric structure brought in including theperiod and thickness of the defect

As shown in Figure 4 a narrow transmission peak canbe observed in the center of the photonic band gap Thephotonic crystal structure with fewer periods had a shallowerforbidden band gap and greater bandwidth This meant thatthe impurity level was created in the photonic band gapand the transmission peak can be used to guide the visibleemitting light of the organic material out

The transmission spectra of the photonic crystal withdifferent thickness of defect layer (100 110 120 130 and140 nm) were shown in Figure 5 It could be found that therewas little impact on the spectrum with different thicknesscompared with that of Figure 4 Even the location of thetransmission peak had drifted to the longer wavelength with

OH

HC

N

N

HC

OH

Figure 6 Chemical structure formula of Lumogen S0790

the thickness increasing of the defect layers the emissionpeaks of fluorescent material still fell into the response bandthe Si-based detectors It is of great help for us to fabricatethe UV-sensitive devices based on the photonic crystal withfluorescent material

3 Experiment

The fluorescent material used for defect layer was LumogenS0790 made by company BASF The chemical structureformula was shown in Figure 6 There were fluorescentphenyl groups in the molecular and hydroxyl group thathad function of fluorescent auxochromeThis structure couldmake the internal electronic of themolecular in transition sothe molecular group absorbed ultraviolet light and emittedvisible light at the same time It was found that this materialemitted strong visible light near 525 nm under the irradiationof wide range of ultraviolet light

Based on the properties of the organic fluorescent mate-rial the photonic crystal was designed as follows air | topreflective mirror | defect layer | bottom reflective mir-ror | substrate The structure of the top reflective mirrorwas (H1015840L1015840)and119898H1015840 and the bottom reflective mirror was(HL)and119899H H was one layer of high refractive index materialZrO2 while L was one low SiO

2 H1015840 and L1015840 were not a quarter

attribute film system and 119898 and 119899 were the number of therepeat period

The reflective mirrors were prepared by electronic beamevaporation method with baking temperature 200∘C andultimate pressure 1 lowast 10minus4 Pa And the defect layer was pre-pared by resistance heat evaporation with baking tempera-ture 40ndash60∘C and ultimate pressure 8 lowast 10minus4 Pa

4 Discussion

Thetransmittance spectra of themirror samplewere obtainedby the spectrophotometer (PerkinElmer Lambda 1050) Thetransmission spectrumof the top reflectivemirror was shown


250 300 350 400 450 500 550 600 6500

10

20

30

40

50

60

70

80

90

100

Top mirror

Tran

smitt

ance

()

Wavelength (nm)

Figure 7 The transmitted spectrum of top HR mirror

350 400 450 500 550 600 650 700

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

Wavelength (nm)

Bottom mirror

Figure 8 The transmitted spectrum of bottom HR mirror

in Figure 7 The average transmittance at 250ndash400 nm wasabout 85 which satisfied the input of the ultraviolet lightto the microcavity The bandwidth was nearly 70 nm and theaverage transmittance was 4 The transmission spectrumof the bottom reflective mirror was shown in Figure 8 Thebandwidth was nearly 75 nm and the average transmittancewas 7

The transmission spectrum of the photonic crystal inthe form of Fabry-Perot microcavity was shown in Figure 9The transmittance of the peak was nearly 601 and the fullwidth half maximum was nearly 11 nm while width of thetwo cut-off bands was 80 nm and 54 nm respectively Andthe transmittance of the cut-off bands was only 2 and 1respectively

The photoluminescence (PL) spectra of the photoniccrystal were shown in Figure 10 which were obtained by flu-orescence spectrometer (Horiba Aqualog DualFL-UV-NIR)The studied excitation wavelength was 250 nm 300 nm and

200 250 300 350 400 450 500 550 600 650 700

0102030405060708090

Tran

smitt

ance

()

Wavelength (nm)

Photonic crystal

Figure 9 The transmitted spectrum of one-dimensional photoniccrystal

330 nm respectively It was found that he PL efficiency wasall enhanced effectively and obviously at the three selectedultraviolet wavelength The peak intensity increased nearlyby 62 at the excitation of 250 nm 90 at 300 nm and 57at 330 nm By integration of the intensity of the emissionspectrum there was a greater enhancement of PL efficiencyand conversion efficiency for UV to visible light

5 Conclusion

In this paper a one-dimensional photonic crystal in the formof Fabry-Perot microcavity with the structure of dielectricmirror and phosphor coating was simulated and fabricatedThe photoluminescence efficiency of the fluorescent materialwas investigated By emission spectrum we could find thatthe photoluminescence intensity of Lumogen fluorescentmaterial has been significantly improved Our study providesa feasibility of developing front illuminated CCD devices forUV light detection with higher sensitivity


350 400 450 500 550 600 650 700 7500

800

1600

2400

3200

4000

4800

5600In

tens

ity (a

u)

Photonic crystalLumogen

Wavelength (nm)

(a)

350 400 450 500 550 600 650 700 750 800

Inte

nsity

(au

)


Wavelength (nm)

9600

8400

7200

6000

4800

3600

2400

1200

0

(b)

400 450 500 550 600 650 7000

1900

3800

5700

7600

9500

11400

Inte

nsity

(au

)


Wavelength (nm)

(c)

Figure 10 PL spectrum of one-dimensional photonic crystal excited at 250 300 330 nm

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was partially supported by the NationalScience Instrument Important Project (2011YQ14014704)Shanghai Municipal Science Instrument Important Project(14142200902) and National Natural Science Foundation ofChina (61378060 and 61205156)

References

[1] E Yablonoviteh ldquoInhibited spontaneous emission in solid-statephysics and electronicsrdquo Physical Review Letters vol 58 no 20pp 2059ndash2061 1987

[2] S John ldquoStrong localization of photons in certain disordereddielectric superlatticesrdquo Physical Review Letters vol 58 no 23pp 2486ndash2489 1987

[3] M M Voronov E L Ivchenko M V Erementchouk L IDeych and A A Lisyansky ldquoPhotoluminescence spectroscopyof one-dimensional resonant photonic crystalsrdquo Journal of Lum-inescence vol 125 no 1-2 pp 112ndash117 2007

[4] I D Block P C Mathias S I Jones L O Vodkin and B TCunningham ldquoOptimizing the spatial resolution of photoniccrystal label-free imagingrdquo Applied Optics vol 48 no 34 pp6567ndash6574 2009

[5] V Chaudhery M Lu C-S Huang et al ldquoLine-scanning detec-tion instrument for photonic crystal enhanced fluorescencerdquoOptics Letters vol 37 no 13 pp 2565ndash2567 2012

[6] N Takada T Tsutsui and S Saito ldquoControl of emissioncharacteristics in organic thin-film electroluminescent diodesusing an optical-microcavity structurerdquo Applied Physics Lettersvol 63 no 15 pp 2032ndash2034 1993


[7] P Schouwink H von Berlepsch L Dahne and R F MahrtldquoObservation of strong excitonndashphoton coupling in an organicmicrocavity in transmission and photoluminescencerdquo Journalof Luminescence vol 94-95 pp 821ndash826 2001

[8] X Y Liu L X Wang Y Liu et al ldquoSpontaneous emissionproperties of organic film in plane optical microcavityrdquo ThinSolid Films vol 363 no 1 pp 204ndash207 2000

[9] BMasenelli S Callard A Gagnaire and J Joseph ldquoFabricationand characterization of organic semiconductor-based micro-cavitiesrdquoThin Solid Films vol 364 no 1 pp 264ndash268 2000

[10] SDirr SWieseH-H Johannes et al ldquoLuminescence enhance-ment in microcavity organic multilayer structuresrdquo SyntheticMetals vol 91 no 1ndash3 pp 53ndash56 1997

[11] G OMueller RMueller-Mach E Alinsog H Lee andD Har-rison ldquoMicrocavity effects in thin-film electroluminescencerdquoJournal of Luminescence vol 72ndash74 pp 1002ndash1004 1997

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CatalystsJournal of


0

20

40

60

80

100

1205961205960

05 10 15 20 25 30 35

Tran

smitt

ance

()

Figure 1 Transmission spectrum of one-dimensional photoniccrystal at 0∘ incidence

300 400 500 600 700 800 900

0102030405060708090

100

57

911

Refle

ctan

ce (

)

Wavelength (nm)

Figure 2 Reflective spectrum of 5 7 9 and 11 periodic dielectricmultilayer

where 119899119886and 119899

119887are the refractive indexes of two different

media For the limited periodic structure material we coulduse the transfermatrixmethod to get the transfer characteris-tic of themembrane reactor By the above theory the reflectivespectra of the films with period of 5 7 9 and 11 respectivelycan be obtained as shown in Figure 2The period mentionedhere refers to a pair of membrane consisting of two differentmediums A and B Theoretically the photonic crystal shouldhave infinite structure but in practice thewidth of the energygap basically no longer changes as long as there is a certainnumber of periods as shown in Figure 2 So the traditionalhigh antimembrane can be regarded as a kind of one-dimensional photonic crystal and the finite membrane stackshould also be considered a special case of one-dimensionalphotonic crystal So the research of fluorescent materialenhancement can be discussed combined with thin solid filmoptical theory with the theory of the photonic crystal

When the fluorescent material is doped in photoniccrystal an impurities defect mode in the photonic band gap

Reflector A Reflector B SubstrateFluorescentmaterial

Figure 3 Structure design of one-dimensional photonic crystal

would be created It would change the light propagationmodeand the density of states The enhancement ratio can beobtained by comparing the density of states in free space andphotonic crystal According to the gold Fermirsquos rule the ratioof spontaneous emission in photonic crystal and free spacewas decided by the ratio of the density of states The densityof states in free space was given by

120588119894(120596) =

1

119881

sdot

119889119873

119889119881

=

1205962

12058721198623=

4119899

119888

(2)

where 119899 was the refractive index of medium 119888 was thespeed of light in vacuum and 119881 was the mode volume 119862 isassociated with parameters and frequency of the dipole of theincident photonThe density of states in photonic crystal wasgiven by

120588119888 (120596) =

1

120575120596119881

=

119899

119888

sdot radic10119865 119865 =

4119877

(1 minus 119877)2 (3)

where 119865 was the degree coefficient and 119877 was the reflectivityof the mirror There is only single mode where bandwidth is120575120596 and the frequency is 120596 So the ratio of the statersquos densityof photonic crystal and free space that was represented by119872was given by

119872 =

radic40119877

4 (1 minus 119877)

(4)

So the value of119872 was decided by the reflectance 119877 and isgreater than 1 in the case of119877 gt 90Thatmeant the photoniccrystal can improve the rate of spontaneous emission andone dimensional photonic crystal structure can effectivelyenhance the luminous efficiency of organic light-emittingmaterials

As shown in Figure 3 there was a fluorescent layer asdefect in our designed photonic crystal structure In order tomake the UV detecting light incentive fluorescent materialthe reflective mirror A was designed that the UV band lightcould pass through and a certain band gap with the centerwavelength of 525 nmWhile the reflective mirror B was onlydesigned with a band gap of certain bandwidth in the centerof 525 nm So this was a photonic crystal with asymmetric


350 400 450 500 550 600 650 700 750 800

0102030405060708090

100

Tran

smitt

ance

()

Wavelength (nm)

34

56


350 400 450 500 550 600 650 700 750 8000

102030405060708090

100

Tran

smitt

ance

()

Wavelength (nm)

140nm130nm

120nm110nm100nm





OH

HC

N

N

HC

OH



3 Experiment






4 Discussion



250 300 350 400 450 500 550 600 6500

10

20

30

40

50

60

70

80

90

100

Top mirror

Tran

smitt

ance

()

Wavelength (nm)


350 400 450 500 550 600 650 700

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

Wavelength (nm)

Bottom mirror





200 250 300 350 400 450 500 550 600 650 700

0102030405060708090

Tran

smitt

ance

()

Wavelength (nm)

Photonic crystal



5 Conclusion



350 400 450 500 550 600 650 700 7500

800

1600

2400

3200

4000

4800

5600In

tens

ity (a

u)


Wavelength (nm)

(a)

350 400 450 500 550 600 650 700 750 800

Inte

nsity

(au

)


Wavelength (nm)

9600

8400

7200

6000

4800

3600

2400

1200

0

(b)

400 450 500 550 600 650 7000

1900

3800

5700

7600

9500

11400

Inte

nsity

(au

)


Wavelength (nm)

(c)




Acknowledgments


References






















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


350 400 450 500 550 600 650 700 750 800

0102030405060708090

100

Tran

smitt

ance

()

Wavelength (nm)

34

56


350 400 450 500 550 600 650 700 750 8000

102030405060708090

100

Tran

smitt

ance

()

Wavelength (nm)

140nm130nm

120nm110nm100nm





OH

HC

N

N

HC

OH



3 Experiment






4 Discussion



250 300 350 400 450 500 550 600 6500

10

20

30

40

50

60

70

80

90

100

Top mirror

Tran

smitt

ance

()

Wavelength (nm)


350 400 450 500 550 600 650 700

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

Wavelength (nm)

Bottom mirror





200 250 300 350 400 450 500 550 600 650 700

0102030405060708090

Tran

smitt

ance

()

Wavelength (nm)

Photonic crystal



5 Conclusion



350 400 450 500 550 600 650 700 7500

800

1600

2400

3200

4000

4800

5600In

tens

ity (a

u)


Wavelength (nm)

(a)

350 400 450 500 550 600 650 700 750 800

Inte

nsity

(au

)


Wavelength (nm)

9600

8400

7200

6000

4800

3600

2400

1200

0

(b)

400 450 500 550 600 650 7000

1900

3800

5700

7600

9500

11400

Inte

nsity

(au

)


Wavelength (nm)

(c)




Acknowledgments


References






















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


250 300 350 400 450 500 550 600 6500

10

20

30

40

50

60

70

80

90

100

Top mirror

Tran

smitt

ance

()

Wavelength (nm)


350 400 450 500 550 600 650 700

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

Wavelength (nm)

Bottom mirror





200 250 300 350 400 450 500 550 600 650 700

0102030405060708090

Tran

smitt

ance

()

Wavelength (nm)

Photonic crystal



5 Conclusion



350 400 450 500 550 600 650 700 7500

800

1600

2400

3200

4000

4800

5600In

tens

ity (a

u)


Wavelength (nm)

(a)

350 400 450 500 550 600 650 700 750 800

Inte

nsity

(au

)


Wavelength (nm)

9600

8400

7200

6000

4800

3600

2400

1200

0

(b)

400 450 500 550 600 650 7000

1900

3800

5700

7600

9500

11400

Inte

nsity

(au

)


Wavelength (nm)

(c)




Acknowledgments


References






















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


350 400 450 500 550 600 650 700 7500

800

1600

2400

3200

4000

4800

5600In

tens

ity (a

u)


Wavelength (nm)

(a)

350 400 450 500 550 600 650 700 750 800

Inte

nsity

(au

)


Wavelength (nm)

9600

8400

7200

6000

4800

3600

2400

1200

0

(b)

400 450 500 550 600 650 7000

1900

3800

5700

7600

9500

11400

Inte

nsity

(au

)


Wavelength (nm)

(c)




Acknowledgments


References






















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Research Article Enhancement of UV Excited...

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