Synthesis and luminescence properties of Cr₂O₃-CaO-GeO₂ glass and glass ceramics for broadband NIR-LEDs

We report the fabrication of novel 0.1Cr(2)O(3)-25CaO-75GeO(2) glass and glass ceramics with wideband NIR luminescence and the annealing temperature dependence of the photoluminescence (PL) properties for applications as NIR phosphors. The anisotropic growth of Ca2Ge7O16 nanocrystals in the annealing samples was confirmed. Annealing-induced variations in the body colors and diffuse reflectance spectra suggest that change in the valence of Cr ions and their coordination environments. Broadband luminescence of 700-1300 nm attributed to the T-4(2) & RARR; (4)A(2) transition of Cr3+ was observed for the as-made glass. The peak wavelength is shifted from 860 to 780 nm, and line-shaped E-2 & RARR; (4)A(2) emission appears due to the crystallization of Ca2Ge7O16 by heat treatment. The PL quantum yield reaches the maximum at 0.19 when the sample is annealed at 775 & DEG;C, and the dependence on annealing temperature can be understood by the change in the PL lifetimes and diffuse reflectance spectra.