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Thermoluminescence of LuPO4:0.1%Yb3+ sintered ceramics was investigated and simultaneous infrared 2F5/2 → 2F7/2 and UV-blue (YbCT3+)* → O2- charge transfer emissions of the Yb3+ impurity were observed around 150 °C (423 K) for the first time. Both photons were generated by one excited Yb3+*. LuPO4:Yb3+ was thus proved to be the first system showing the quantum cutting effect in thermoluminescence. Low concentration of the dopant was proved crucial to observe an intense CT emission at so high temperatures. These data revise deeply those reported previously on the thermal quenching of Yb3+ charge transfer luminescence in orthophosphates. In was formerly claimed that CT luminescence of Yb3+ in LuPO4 and similar hosts is quenched below 300 K. Similarly, the thermoluminescent emission of LuPO4:Yb3+ above room temperature was previously reported to appear only in the IR part of the spectrum around 980 nm. Our results fundamentally change this picture and prove that CT luminescence of Yb3+ in orthophosphates appears to be significant even above 150 °C (423 K). We demonstrate the great significance of the activator concentration in its CT luminescence thermal quenching. The Yb3+ impurity ion was found to act both as an electron trap and as a recombination center. Our data open the possibility to generate intense CT luminescence of Yb3+ in orthophosphates at room temperature and above which may make such phosphors rational for applications previously considered unattainable for them.

Luminescence properties of SrS:Ce pellets sintered at 1700 °C were investigated under high pressure. Two different Ce3+-related emissions were confirmed to appear in the blue-green and red parts of the spectrum and were shown to shift significantly and linearly to longer wavelengths with increasing pressure. Changes in decay times of both emissions were also thoroughly analyzed. The results confirmed that Ce3+ ion pairing/clustering occurring due to their enhanced mobility at high temperatures is responsible for the appearance of the recently reported red Ce3+ emission in sintered SrS:Ce pellets.