Effect of thermal treatment on luminescence and VUV-to-visible conversion in oxyfluoride glass singly doped with praseodymium and thulium

Oxyfluoride glasses with composition 50GeO₂-(50 - x)PbO-xPbF₂ (x <= 15mol%) containing praseodymium or thulium were melted from commercial raw materials in normal atmosphere. Glass samples were then thermally treated in order to achieve controlled precipitation of PbF ₂. The effect of thermal treatment on the relaxation of excited levels within 4fⁿ configurations of praseo-dymium and thulium is found to be qualitatively similar. Non-exponential decay curves of luminescence in as-melted glasses become nearly exponential with corresponding longer lifetimes in thermally treated samples. Substantially different behavior of samples containing praseodymium with respect to those containing thulium has been found upon excitation in the 50-300 nm spectral region. Efficient VUV-excited visible emission has been recorded with both as-melted and thermally treated glass containing Pr³⁺. No visible emission has been recorded upon VUV excitation of glass and glass-ceramics samples containing thulium.