Transparent glass ceramics containing &bgr;‐PbF2:Tm3+crystallites have been prepared by heat treatment of glasses in GeO2‐PbO‐PbF2‐TmF3system. Average crystallite size of &bgr;‐PbF2evaluated from the full width at half maximum of x‐ray diffraction lines varies from about 16 to 20 nm as the heat treatment temperature increases from 340 to 400 °C when 50GeO2⋅40PbO⋅10PbF2⋅1TmF3glass is heat treated. The glass ceramics containing &bgr;‐PbF2:Tm3+of 16 nm is transparent in the visible region. The incorporation of Tm3+into &bgr;‐PbF2crystalline phase has been demonstrated from the linewidth and peak position of optical absorption spectrum. Frequency upconversion fluorescence has been observed for the transparent glass ceramics at room temperature. The upconversion fluorescence intensities due to the1D2→3H6and1D2→3F4transitions are higher for the transparent glass ceramics than for the glass. This phenomenon is explainable by assuming that the multiphonon relaxation rate of the3H4state is smaller in the glass ceramics than in the glass. ©1995 American Institute of Physics.