CdSe/ZnS-doped silicophosphate films prepared by sol-gel method

Silicate and silicophosphate films doped with CdSe/ZnS quantum dots (QDs) have been deposited on silicon substrate, by sol-gel method, spin-coating technique. A precursor solution (PS) composed of tetraethoxysilane (TEOS) and ethanol (EtOH) has been prepared in the case of silicate films (T) and in the case of silicophosphate films (TPT), the same precursors for T films and triethylphosphate were used. In each PS, dimethylformamide and CdSe/ZnS (QD) were added. Spectroscopic ellipsometry shows that absorption of TPT films in the visible (400-700 nm) decreases over 400 nm, due to dimensional quantum effect of semiconductor doping particles embedded in the silicophosphate matrix. The same manner is noticed in the case of refractive index dependency on wavelength. Raman spectra were recorded by 785 nm excitation and put in evidence specific bands for the inorganic matrix as well as a low-intensity band characteristic for CdSe doping. The morphology of the films was investigated by transmission electron microscopy revealing semiconductor doping dots with average dimension 3.3 nm and a homogeneous distribution of the doping particles in the inorganic matrix. SEM image of the cross-section of the TPT film reveals a thickness of about 500 nm. The fluorescence spectra of CdSe/ZnS-doped films exhibit an emission band at about 530 nm, provided by 350 nm excitation, whose characteristics are close to those of CdSe compound.