Spectroscopic study of Cr5+ doped and Cr5+ nanoclusters embedded porous sol-gel SiO2 glasses

In this study two kinds of samples, Cr doped and Cr nanoclusters embedded in porous SiO2 glasses were prepared. Broad band emissions at 620 and 560 nm were observed, respectively, from the doped and the embedded samples annealed at 800°C. The lifetimes of the emission of both samples are of the order of microseconds at room temperature. These results indicate that most of Cr ions are in a pentavalent state. The intensity of the fluorescence of the Cr5+ nanoclusters-embedded SiO2 samples degraded slowly with exposure time to laser irradiation. The fluorescence intensity recovers in a few hours after turning off the laser irradiation. The phenomenon is ascribed to the migration of Cr5+ nanoclusters on the surfaces of the pores due to thermal heating.