Oxyfluoride glasses with the composition 50SiO(2) . 50PbF(2) . xErF(3) (x=4 and 5) by molar ratio were developed. Transparent glass ceramics were obtained by heat-treating the 50SiO(2) . 50PbF(2) . xErF(3) glasses at the first crystallization temperatures. X-ray diffraction analysis of the transparent glass ceramics revealed that fluorite type beta-PbF2 : Er3+ solid solution regions of about 13.0 nm in diameter are precipitated in the glass matrix. The formation of this beta-PbF2 : Er3+ solid solution was also supported by Eu3+ fluorescence spectra which were measured on specimens in which Eu substituted for Er. Under 800 nm laser excitation, the Er3+ upconversion luminescence of 50SiO(2) . 50PbF(2) . xErF(3) glasses was barely detectable, but the 50SiO(2) . 50PbF(2) . xErF(3) glass ceramics gave Er3+ upconversion luminescence at a very high efficiency. The reason for the highly efficient Er3+ upconversion luminescence in the 50SiO(2) . 50PbF(2) . xErF(3) glass ceramics can be explained in terms of the very small multiphonon relaxation rates that are anticipated from consideration of the Eu3+ emission spectra.