Yb3+-Yb3+ cooperative upconversion in oxyfluoride glass and glass ceramics

Yb3+-doped oxyfluoride glasses and glass ceramics containing KZnF3 nanocrystals were obtained by melt-quenching. Under excitation of a 980 nm laser, a strong blue emission from Yb3+-Yb3+ cooperative upconversion was observed in the glass sample, which increased by five times in glass ceramics after heat treatment for 20 h. The photoluminescence mechanism and sample properties were investigated by X-ray diffraction, transmission electron microscopy, fluorescent lifetime, absorption and emission spectra. The size of KZnF3 nanocrystals is in the range 5 nm–20 nm, making the glass ceramic samples highly transparent. The STEM-EDS measurements indicate that the distribution of Yb is consistent with that of the KZnF3 nanocrystals. Fluroide phase provides a low-phonon-energy environment for Yb3+-Yb3+ ion pairs, which facilitates an intense fluorescent blue emission in the KZnF3 crystal lattice. Both theoretical and experimental results demonstrate that Yb3+-doped oxyfluoride glasses and glass ceramics containing KZnF3 nanocrystals are promising materials for blue upconversion emission.