Preparation and optical properties of transparent glass‐ceramics containing β‐PbF2:Tm3+

Transparent glass ceramics containing β‐PbF2:Tm3+ crystallites have been prepared by heat treatment of glasses in GeO2‐PbO‐PbF2‐TmF3 system. Average crystallite size of β‐PbF2 evaluated 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⋅1TmF3 glass is heat treated. The glass ceramics containing β‐PbF2:Tm3+ of 16 nm is transparent in the visible region. The incorporation of Tm3+ into β‐PbF2 crystalline 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 the 1D2→3H6 and 1D2→3F4 transitions are higher for the transparent glass ceramics than for the glass. This phenomenon is explainable by assuming that the multiphonon relaxation rate of the 3H4 state is smaller in the glass cerami...