Spectroscopic studies of chromium-doped silica sol-gel glasses

The results of EPR and optical measurements of Cr-doped silica glasses obta ined by means of sol-gel technology are presented. The effect of Cr concent ration on optical behavior was studied. Thermoluminescence was observed aft er heating previously cooled and UV irradiated samples. The EPR measurement s were performed for UV irradiated samples and a strong temperature depende nce of the signal was noticed. The nature of optically active Cr centers wa s discussed. It is concluded that the EPR signal is associated with the Cr5 + ions at tetrahedral sites whereas the emission is attributed to the ligan d-metal charge transfer transitions of Cr6+ ions coupled to Cr5+. No eviden ce was found for the presence of Cr3+ ions in silica gel glass. (C) 2001 El sevier Science B.V. All rights reserved.