Oxy-fluoride glass ceramics containing CaF2, crystals doped with YbF3-LnF(3) (Ln = Er, Tm) were prepared by heat-treatment from SiO2-Al2O3-CaO-CaF2 glasses. The upconversion emission spectra of Er3+ and Tm3+ ions in the visible range were measured by 970 nm pumping. In the spectrum of the Er doped sample, 540 nm upconversion band due to the S-4(3/2)-I-4(15/2) and 660 nm band due to the F-4(9/2)-I-4(15/2) were observed. In the Tm doped sample, a blue upconversion emission band due to the (1)G(4)-H-3(6) was observed at 480 nm as well as an 800 nm band. The intensity of these upconversion emissions were very weak in the corresponding as-made glasses. These results indicate that rare-earth ions are incorporated in the CaF2 crystal phases after crystallization and the energy transfer efficiency from Yb3+ to Er3+ or Tm3+ are dramatically improved. (c) 2005 Elsevier B.V. All rights reserved.