Figure 1

(a) Absorption and (b) photoluminescence spectra of the as-prepared and heat-treated glasses with the compositions of C1, C2, C3, and C4, (c) photoluminescence and excitation spectra of C4 specimen heat-treated at 530 °C for 10 h.
(a) Absorption and (b) photoluminescence spectra of the as-prepared and heat-treated glasses with the compositions of C1, C2, C3, and C4, (c) photoluminescence and excitation spectra of C4 specimen heat-treated at 530 °C for 10 h.