Fabrication and Efficient Infrared‐to‐Visible Upconversion in Transparent Glass Ceramics of Er–Yb Co‐Doped CaF 2 Nano‐Crystals

Transparent glass ceramics containing CaF 2 nano‐crystals co‐doped with Er–Yb were developed by heat treatment of glasses in the system SiO 2 –Al 2 O 3 –CaF 2 –LnF 3 (Ln=Er, Yb). The crystal size of CaF 2 increased with increasing heat‐treatment temperature. Upconversion 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 CaF 2 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 CaF 2 nano‐crystals, and the quantum efficiency of Er 3+ ‐luminescence and the energy transfer efficiency from Yb 3+ were considerably improved after ceramization.