Oxyfluoride glasses with composition of 45SiO(2)center dot 20Al(2)O(3)-30PbF(2)center dot 5ZnF(2) by molar ratio with a high stability against crystallization have been obtained by melt quenching. After doping with x (x = 1, 2, 4) mol% of Er3+ transparent or translucent glass-ceramics could be formed. The structural transformations of these materials were investigated by thermal analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Spherical polycrystalline aggregates comprised of many nanosized and randomly oriented beta-PbF2 grains were embedded separately among glassy matrix. On heating these nanosized grains merge with their neighbors to form bigger single crystals in a way like Ostwald ripening. The size modification of polycrystalline aggregates in the samples was found to be dependent on Er3+ doping. (C) 2005 Elsevier Ltd. All rights reserved.