LUMINISCENCE STUDIES OF NANOMATERIALS FOR

OPTOELECTRONIC APPLICATIONSKamal Kumar Kushwah* and Parveen Ansari

Department of Applied Physics, Jabalpur Engineering College, Jabalpur, M.P., India.

*Corresponding Author: kamal_kushwah2005@yahoo.com

ABSTRACT

The nanocomposite films of ZnSe nanocrystals in polyvinyl alcohol (PVA) matrix weresynthesized by environmental friendly chemical method for optoelectronic Applications.These composites were characterized by X-ray diffraction and AFM, which indicates thehexagonal crystalline structure with particle size up to a few nm. The Particle size is foundto decrease by increasing PVA Concentration. The photoluminescence properties of thesecomposite films with varying concentration of PVA and Zn have been investigated.This may be useful for their potential application in anti-reflection coating, display devicesand optical sensors. Micro Hardness of these nanocomposites was also measured byVicker hardness tester and its dependence with varying load and mechanical behavior ofsamples was discussed.

INTRODUCTION• Polymer- inorganic nanocomposites have

attracted much attention recently due to their unique size dependent chemical and physical properties [1].

• ZnSe nanocomposites exhibit size dependent tunable photoluminescence [2].

• Studies have been under taken to prepare ZnSe nanoparticles in PVA matrix and investigate their Photo luminescence.

EXPERIMENTAL

• ZnSe/PVA Nanocomposites were prepared bychemical method.

• First PVA solution was prepared in distilledwater and then 1 ml ZnCl2 solution was addedto it for ZnSe/PVA.

• After setting the pH by NH3 solution at 10, 1ml of freshly prepared Na2SeSO3 solution wasadded and stirred for 90 minutes to obtainZnSe/PVA nanocomosite.

• The solution was spread on glass plates and on solvent evaporation nanocomposites films were obtained.

• A number of samples were prepared withvaring Zn2+ content and different PVAconcentrations and subjected to X-raydiffraction and photoluminescence and AFMinvestigations.

XRD

• XRD pattern reveals cubic structure for ZnSe/PVA.

• Three Peaks are obtained at 2θ=27.57˚, 45.59˚, 53.27˚ indicating reflection from (111), (220), (311) planes for ZnSe/PVA.

• The peak corresponding to 2θ=20˚ represents PVA matrix.

Fig.1. XRD pattern of

ZnSe/PVA

• The Particles size of samples computed from Debye Scherrer formula are obtained up to 13nm.

• The Particle size is found to decrease by increasing PVA Concentration.

• PVA is acting as capping agent and by increasing its concentration smaller ZnSe particles are formed in its matrix.

• higher intensity isobserved by increasingPVA content in ZnSenanocomposite filmswithout any change inposition of PL peak.

• Higher intensity isobtained for smaller ZnSein PVA matrix. 440 450 460 470 480 490 500 510

-200

0

200

400

600

800

1000

1200

1400

1600

1800

In

te

nsity (a

.u

.)

Wavelength in nm

S5

S4

S3

S2

S1

Fig.2 Photoluminescence

Spectra of ZnSe/PVA

Samples with different PVA

ConcentrationsNATIONAL CONFERENCE ON LUMINESCENCE AND ITS APPLICATIONS (NCLA-2014) 5-7TH February, 2014, Jabalpur, India

• The emission may be attributed to band to band transition of which is greater than bulk band gap of ZnSe.

• The oscillator strength is increased by reducing the size which enhances the PL intensity.

• Due to proper passsivation of surface states non radiative transitions are not increased which enhance the PL intensity.

• The Photoluminscencespectra of ZnSe/PVAwith variations of Zn2+

content excited by325nm(fig.3)

• It shows blue shiftwith lower particle sizedue to quantumconfinement effect.

Fig.3 Photoluminescence Spectra

of ZnSe/PVA Samples with varying

Zn2+ Content.

Wavelenth in nm

Wavelength (nm)

Int.

Refractive Index Measurements

• Optically transparent ZnSe/PVAcomposite Samples of comparativelylarger thickness are prepared andobtained in thin film form.

• All prepared films exhibit excellent opticaltransparency in the visible region.

• The Refractive index of these compositeswas measured at sodium line (5893Å)with the help of Abee’ refractometer andwas found in the range of 1.695-1.730

NATIONAL CONFERENCE ON LUMINESCENCE AND ITS APPLICATIONS (NCLA-2014) 5-7TH February, 2014, Jabalpur, India

Microhardness Measurements• Micro-hardness of these nanocomposites was also measured

by Vicker hardness tester-Vaiseshika microhardness tester 7005.

• It is seen that hardness increases with small size of

Nanocomposite.

0

5

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25

10 20 30 40 50 60 70 80

HV4

HV3

HV2

HV(PURE PVA)

HV1

load(g)

Mic

roh

ard

nes

s(K

g/m

m2)

Fig.4

AFM Measurements

• The Particle sizes from AFMimage is below than 50nmshows strong aggrementwith those obtained fromXRD.

• I have shown some of theAFM Pictures of ZnSe/PVAnanocomposites.

29.5 nm

43 nm

5.CONCLUSION

• Thus ZnSe/PVA Nanocomposites can be synthesizedby very simple chemical route.

• XRD analysis revealed that, increasing PVAconcentration in ZnSe/PVA composites, particle sizeis reduced.

• The average particle size of ZnSe reduces onincreasing PVA concentration and Zn2+ content inZnSe/PVA composites.

• PL intensity is also increased due to enhancedoscillator strength in nanoparticles.

• The polymer matrix acts to stabilize the nanoparticle.

• It is seen that refractive index decreases withincreasing polymer concentration.

• Hardness increases with smaller size andfollows meyer’s law for n>2.

• This may be useful for their potentialapplication in anti-reflection coating, displaydevices and optical sensors.

• Due to the PL peak in green these compositefilms are promising materials for Optoelectronic Devices.

• Nanocomposites of High refractive index,

enhanced PL intensity are used to prepare

optical display devices like light emitting

diodes (LEDs), Liquid crystal display (LCDs).

Optical applications( www.google.com)

Mechanical application

( www.google.com)

ACKNOWLEDGEMENT

The authors gratefully acknowledge the valuableassistant provided by Inter University consortium(IUC) Indore for characterizing samples by XRD andalso very much thankful to Department ofNanotechnology, MAINAT, Bhopal for PL Studies andto Department of Physics, St. Aloysius College,Jabalpur for refractive index and Microhardnessmeasurements.

REFERENCES

• Indade T T, Neves M C and Barros A M V 2000 Scr Mater 43 567.

• Murray C B, Kaganand C R and Bavendi M G 1995 Science 270 1335.

• Fendler J H and Maldrum F C 1995 Adv Mater 7 607.

• Dabbouri B O, Viejo J R, Mikules F B, Heins J R, Mattonoro H, Ober R, Jonsen K F and Bavendi 1997 J Phys Chem B 101 9463.

NATIONAL CONFERENCE ON LUMINESCENCE AND ITS APPLICATIONS (NCLA-2014) 5-7TH February, 2014, Jabalpur, India

• Platschek V, Schrader B, Herz K, Hilbert U,Ossan W Schottner G, Rahaush O, Bischof T, Lermann G,Malemy A, Keifer W,Bacher G, Forchel A, Su D, Glusig M. Muller G and Spanhal L 1997 J Phys Chem B 101 8898.

• Chan W C W and Nie S M, 1998 Science 2812016.

• Murugadoss G, Rajamanan B and Ramasamy V 2010 Dig. J.of Nano. and Bio 5 339-345.

Thanks for your attention

NATIONAL CONFERENCE ON LUMINESCENCE AND ITS APPLICATIONS (NCLA-2014) 5-7TH February, 2014, Jabalpur, India