Ca2GeO4:Cr4 + transparent nano-glass ceramics

Abstract The purpose of this study was to find out glass compositions permitting to obtain glass-ceramics of the Cr 4 + :Ca 2 GeO 4 nanophase with a proper condition of syntheses and satisfying the requirements for transparent glass-ceramic. Three series of glass compositions were investigated, containing CaO, GeO 2 and the glass formers: CaO-GeO 2 -B 2 O 3 , CaO-GeO 2 -Na 2 B 4 O 7 and CaO-GeO 2 -LiBO 2 . The comparison between the three systems clearly shows that CaO-GeO 2 -LiBO 2 offers significantly better conditions for obtaining glass ceramics containing Ca 2 GeO 4 nanophase, as regards the temperature of melting and homogenization of the glasses (1100–1150 °C) and the possibility of obtaining Ca 2 GeO 4 , as a phase into the glass. It was established that because of the big difference between the speed of nuclei and the speed of particle growth, particles at about 50 nm at high degree of crystallization can be received. Transmission and photoluminescence spectra are measured and show that the active ion is Cr 4 + . A broad–band of emission in the range of 1000–1600 nm was established.