Modification by thermal annealing of the luminescent characteristics of CdSe quantum dots in gelatin films

The influence of thermal annealing on the photoluminescence (PL), PL excitation (PLE) and Raman scattering spectra of CdSe quantum dots (QDs) in gelatin films is studied. The X-ray diffraction reveals the presence of CdSe QDs with a size of about 3 nm in the film. Thermal annealing of the QDs at 100 degrees C in air results in a red shift of the PL bands as well as in changes in the temperature dependence of the PL intensity. In the PLE spectra the maximum associated with the light absorption by the QDs shifts to the red region also. The effects are found to be reversible. The passivation of CdSe nanocrystals with ZnS shell reduces the effects. In the Raman scattering spectra, the position of LO phonon peak of CdSe QDs does not change upon annealing. The effects are explained by the break of the bonds of cadmium surface atoms with functional groups of gelatin molecules. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim