Photon avalanche upconversion in Ho3+–Yb3+ co-doped transparent oxyfluoride glass–ceramics

The Ho3+–Yb3+ co-doped transparent glass and glass–ceramics containing CaF2 nanocrystals have been prepared. Differential thermal analysis and X-ray diffraction measurements have been made to characterize thermal properties of glass and structural changes in glass–ceramics, respectively. Photon avalanche upconversion has been achieved by exciting the samples at 745 nm at room temperature. An intense green and a weak red upconverted emissions corresponding to the 5S2:5F4 → 5I8 and 5F5 → 5I8 transitions, respectively, have been observed. The upconversion intensity has been found to increase with the increase in the size of the fluoride nanocrystals in glass–ceramics. Experimental evidences confirm that the mechanism of upconversion is photon avalanche.