Spectroscopy and crystal-field analysis for Cr(IV) in alumino-silicate glasses

Racah parameters of Cr4+ ions in alumino-silicate glasses have been calculated, indicating most Cr4+ ions are located at low-field sites. Using three-peak Gauss fitting for the luminescence lineshape of Cr4+:alumino-silicate glass at low temperatures, the existence of Cr4+ at high-field sites has been demonstrated for the first time in the alumino-silicate glass. The temperature dependence of the emission of low-Cr2O3 glass shows blue shift because most of the Cr4+ ions are in the low-field sites; in which the Cr4+ ions show the large difference of the thermal population at different excited states due to the non-radiative processes. On the other hand, the concentration dependence of the emission of Cr4+ ions in alumino-silicate glass shows red shift, caused by the energy transfer between Cr4+ ions in different crystal-field sites, and subsequently the mechanism of energy transfer between Cr4+ ions at low-field sites and at high-field sites has been proposed.