Photoluminescence and Structural Properties of CdSe Quantum Dot-Polymer Composite Films
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Photoluminescence and Structural Properties of CdSe Quantum Dot-Polymer Composite Films L. Borkovska1, N. Korsunska1, T. Stara1, V. Bondarenko1, O. Gudymenko1, O. Stroyuk 2, O. Raevska 2 and T. Kryshtab3 1
V. Lashkaryov Institute of Semiconductor Physics, NASU, pr. Nauky 41, 03028 Kyiv, Ukraine
2
L. Pysarzhevsky Institute of Physical Chemistry, NASU, pr. Nauky 31, 03028 Kyiv, Ukraine
3
ESFM - Instituto Politécnico Nacional, Av. IPN, Ed.9 U.P.A.L.M., 07738 Mexico D.F.Mexico
ABSTRACT Thermal stability of the luminescent properties of CdSe and CdSe/ZnS quantum dots (QDs) in polymer films of gelatin and polyvinyl alcohol (PVA) is studied. Thermal annealing of the films at the air ambience at 100 oC is found to result in two effects in the photoluminescence (PL) spectra: (i) an enhancement of the PL intensity and (ii) a red spectral shift of the PL bands. The first effect is observed in both QDs-gelatin and QDs-PVA composites, while the second one - in the QDs-gelatin only. The passivation of CdSe QDs with ZnS shell reduces the effects. The enhancement of the PL intensity is supposed to be due to the decrease of nonradiative defect density. The red shift is explained by dissociation of coordination bonds between surface Cd atoms and amino-groups of gelatin. This dissociation decreases the PL intensity too. This effect competes with the effect of PL enhancement and is supposed to be responsible for nonmonotonous dependence of the PL intensity versus annealing time in the QDs-gelatin composite. INTRODUCTION The progress achieved in fabrication of semiconductor quantum dot (QD)-polymer composites made an impact in many applications including optotelectronics, photonics, analytical chemistry and bioengineering [1- 3]. The challenges in present-day applications of semiconductor QDs are their stability and biocompatibility. The release of Cd2+ ions from the core of II-VI QDs (CdSe, CdS, CdTe) in response to ultraviolet radiation has been shown to be the main cause of their cytotoxicity [2, 3]. The gelatin, - natural nontoxic, water-soluble and biodegradable polymer, was proposed as a surface capping agent for CdTe [4], CdSe and CdS [5] QDs. It can also be used as a stabilizing agent during the synthesis of colloidal QDs [5].The possibility to produce CdTe and CdSe QDs embedded in gelatin nanoparticles was demonstrated [6, 7]. The CdTe QDs–gelatin system showed inherent stability against photo-oxidation damage and salt effect [6], as well as biocompatibility and the reduced toxicity [4]. However, thermal stability of QD-gelatin system was not investigated in detail. Here, we present the results of our study of the effect of thermal annealing at 100 oC on the photoluminescence (PL) of composite polymer films with embedded CdSe and CdSe/ZnS QDs. The polymers studied were gelatin and polyvinyl alcohol (PVA). The latter contained a small amount of gelatine which was used as a stabilizing agent during the synthesis of the QDs. EXPERIMENTAL DETAILS
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CdSe and CdSe/ZnS QDs embedded in polymer film of gelatin or PVA deposite
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