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 S-5(2):F-5(4) -> I-5(8) and F-5(5) -> I-5(8) 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. (C) 2014 Elsevier B.V. All rights reserved.