Mixed-Phase Crystallization and Visible Fluorescence in Rare-Earth Ions Doped Germanate Glass-Ceramics

Rare-earth doped glass-ceramics were prepared by heat-treating the precursor germanate glasses. The crystalline phases of the glass-ceramics were assigned to be NaAlGeO4 (NAG) and Mg2GeO4 (MG), and the primary particle sizes were derived to be ~31 and ~32nm, respectively. The secondary particle size of crystal grains was estimated to be ~30µm, and the large grain size is owing to the particles aggregation. Under 254 and 365nm radiation, Sm3+-doped glass-ceramics exhibit orange and reddish-orange fluorescences, and Eu-doped glass-ceramics present red and purplish-red lights, respectively. The investigation results of excitation spectra indicate that the Sm3+- and Eu-doped NAG-MG glass-ceramics can be excited efficiently by commercial UV and blue laser diodes, as well as blue and bluish-green LEDs.