Spectroscopy and crystal-field analysis of Cr4+-doped transparent silicate glass-ceramics

We report transparent Cr4+-doped SiO2-Al2O3-ZnO-Li2O-K2O glass-ceramics with broadband infrared luminescence. After heart-treatment, Li2ZnSiO4 crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. Racah parameters of Cr4+-Li2ZnSiO4 glass-ceramics have been calculated, and it was confirmed from absorption spectra that the energy levels of Cr4+-doped glass-ceramics are close to the cross point 1E and 3T states. No infrared emission was detected in the as-made glass samples, but the broadband infrared emission centered at 1210 nm with the full width at half maximum (FWHM) of more than 250 nm was observed by exciting the glass-ceramics with excitation of an 808 nm laser diode. In order to analyze the located crystal field of Cr4+ ions, the emission spectra are fitted by multi-peak Gauss fitting. It is seen that the fluorescence spectra are fitted into two Gaussian bands at around 1195 and 1263 nm with band widths of 208 and 278 nm, respectively. The two Gaussian bands at around 1195 and 1263 nm have about the same decay rate, and hence they would probably originate from the same luminescent centers. The observed infrared emission could be attributed to Cr4+ ions at low-field sites in Li2ZnSiO4 glass-ceramics.