Photoinduced Enhancement of Photoluminescence of Colloidal II-VI Nanocrystals in Polymer Matrices.

Volodymyr Dzhagan,Oksana Isaieva,Oleksandr Stroyuk,Volodymyr Yukhymchuk,Dietrich R T Zahn,Oleksandr Selyshchev,Mykhailo Valakh,Oleksandra Raievska,Olga Kapush

doi:10.3390/nano10122565

Abstract

The environment strongly affects both the fundamental physical properties of semiconductor nanocrystals (NCs) and their functionality. Embedding NCs in polymer matrices is an efficient way to create a desirable NC environment needed for tailoring the NC properties and protecting NCs from adverse environmental factors. Luminescent NCs in optically transparent polymers have been investigated due to their perspective applications in photonics and bio-imaging. Here, we report on the manifestations of photo-induced enhancement of photoluminescence (PL) of aqueous colloidal NCs embedded in water-soluble polymers. Based on the comparison of results obtained on bare and core/shell NCs, NCs of different compounds (CdSe, CdTe, ZnO) as well as different embedding polymers, we conclude on the most probable mechanism of the photoenhancement for these sorts of systems. Contrary to photoenhancement observed earlier as a result of surface photocorrosion, we do not observe any change in peak position and width of the excitonic PL. Therefore, we suggest that the saturation of trap states by accumulated photo-excited charges plays a key role in the observed enhancement of the radiative recombination. This suggestion is supported by the unique temperature dependence of the trap PL band as well as by power-dependent PL measurement.

Highlights

Semiconductor nanocrystals (NCs) and quantum dots (QDs) prepared by colloidal syntheses represent an ever-growing area of fundamental research that envisages numerous applications [1,2]
We suggest that the saturation of trap states by accumulated photo-excited charges plays a key role in the observed enhancement of the radiative recombination
Synthesis of CdTe NCs stabilized with thioglycolic acid (TGA) in aqueous solution was reported in References [37,38] and of acetate-stabilized ZnO NCs in dimethyl sulfoxide (DMSO) in Reference [39]

Summary

Introduction

Semiconductor nanocrystals (NCs) and quantum dots (QDs) prepared by colloidal syntheses represent an ever-growing area of fundamental research that envisages numerous applications [1,2]. There are studies of the PL spectra of colloidal II-VI NCs under a prolonged illumination in solutions [23,24,25,26,27,28], dried on substrates [29,30,31], and embedded in polymers [23,24,32,33,34,35]. We investigated the evolution of the PL spectra of different types of II-VI NCs, embedded in several polymer matrices, under continuous above-bandgap illumination with laser light. The analysis of this evolution gives information about the durability of certain NC/polymer composites, and helps to shed light on the structure of the NC/polymer interface and the nature of the observed PL emission. We investigated two types of samples: (i) NCs synthesized in the presence of polymers acting as stabilizers and (ii) NCs synthesized (ex situ) using other stabilizers/ligands and subsequently embedded into a polymer

Materials and Methods

Temperature Dependence of PL Spectra

Conclusions