Chromium-oxide enhancement of photo-oxidation of CdSe/ZnS quantum dot solids

Abstract

In this paper, we report the results of depositing CdSe/ZnS quantum dots (QDs) on Cr coated substrates. Compared to such QDs on glass surfaces, the emission peak blueshifts and broadens much more rapidly. The acceleration of the process is presented by showing the relative intensity, position, and full-width as a function of time for various laser intensities, and the effects on photoinduced fluorescence enhancement and photo-oxidiation are discussed. We also consider the thickness of the Cr layer and photo-induced heating, showing this factor should instead lead to a redshift of the peak. Oxidation of colloidal QDs is known to cause blueshifts and broadening of emission peaks (photobleaching). We attribute the faster photobleaching of QDs on Cr films to enhancement in the oxidation of the ZnS shell by catalytic or direct chemical reactions with chromium oxides. As a working hypothesis, this leads to additional paths for breakdown of the otherwise protective nature of the shell.