Transparent glass ceramics containing CaF2 nano-crystals co-doped with Er-Yb were developed by heat treatment of glasses in the system SiO2-Al2O3-Caf2-LnF3 (Ln=Er, Yb). The crystal size of CaF2 increased with increasing heat-treatment temperature. Up conversion emission intensities at 660 and 540 nm increased dramatically with increasing heat-treatment temperature. The cathode luminescence mapping indicates that the visible Er-luminescence arises mainly from the precipitated CaF2 nano-crystals with a phonon energy lower than that of a silicate matrix. It is concluded that both Er and Yb were concentrated in the CaF2 nano-crystals, and the quantum efficiency of Er3+ luminescence and the energy transfer efficiency from Yb3+ were considerably improved after ceramization.
