Photoinduced transformations of optical properties of CdSe and Ag-In-S nanocrystals embedded in the films of polyvinyl alcohol

The results of investigation of photostability of the composites of CdSe and Ag-In-S nanocrystals (NCs) embedded in the films of polyvinyl alcohol (PVA) are presented. The films were studied by photoluminescence (PL), optical absorption, micro-Raman and X-ray diffraction methods. It is found that heating of the films to 100 °C promotes PVA crystallization and stimulates an increase of the PL intensity for the NCs of both types. The latter effect is ascribed mainly to the improvement of NC surface passivation by functional groups of PVA. The illumination with the 409-nm LED's light enhances PL intensity for CdSe NCs and decreases it for Ag-In-S NCs as well as results in the darkening of the films. The color of the Ag-In-S-PVA film restores with time, while the change of the optical properties of the CdSe-PVA composite is irreversible. The possible mechanisms of the revealed effects, such as structural transformations at NC/PVA interface as well as the formation of new light-absorbing species are discussed.