Spectroscopic studies of chromium-doped silica sol–gel glasses

The results of EPR and optical measurements of Cr-doped silica glasses obtained by means of sol–gel technology are presented. The effect of Cr concentration on optical behavior was studied. Thermoluminescence was observed after heating previously cooled and UV irradiated samples. The EPR measurements were performed for UV irradiated samples and a strong temperature dependence of the signal was noticed. The nature of optically active Cr centers was discussed. It is concluded that the EPR signal is associated with the Cr5+ ions at tetrahedral sites whereas the emission is attributed to the ligand–metal charge transfer transitions of Cr6+ ions coupled to Cr5+. No evidence was found for the presence of Cr3+ ions in silica gel glass.