Luminescence of Nanostructured SnO₂-SiO₂ Glass-Ceramics Prepared Sol–Gel Method

Nanostructured silica based glass-ceramics samples of composition (100 – x)SiO₂-xSnO₂, with x from 1 to 10, have been synthesized by thermal treatment of precursor sol–gel glasses. The average size of the obtained SnO₂ nanocrystals, calculated by using the X-ray diffraction, can be predetermined by using well-controlled concentration of tin precursor. The mean radius ranging from 1.6 to 5.5 nm, is comparable to the exciton Bohr radius, corresponding to wide band-gap semiconductor quantum-dots in an insulator SiO₂ glass. A spectroscopy study in terms of optical absorption and photoluminescence spectra has been carried out as a function of SnO₂ concentration. Size-dependent red-shifts of excitation and emission bands, with increasing of tin precursor concentration, point to the quantum confinement effect. The nanocrystal sizes have been obtained and compared by using the Brus and Scherrer equations. The band gap increase is in agreement with results, based on the effective mass model. The recombination of conduction band electron with oxygen vacancies is proposed to explain the luminescence red-shift.