A new photoluminescent feature in LuPO4:Eu thermoluminescent sintered materials
Nanocrystalline powders of LuPO4:Eu were prepared at 230 °C by a hydrothermal method. Their post-treatment at 900, 1200 and 1350 °C induced a moderate grain growth from ∼20–50 nm up to 80–300 nm. These powders were sintered at 1700 °C and such LuPO4:Eu materials, despite the regular Eu3+ emission, produced a broad-band luminescence peaking at around 425 nm at room temperature. The sintered LuPO4:Eu materials also generated an intense thermoluminescence with the maximum around 200 °C. The photoluminescence characteristics of the broad luminescence was performed in the 20–550 K range of temperature. While the intensity of this emission did not change within 20–550 K its decay time dropped from ∼823 μs (20 K) to ∼7 μs only (550 K) with the most potent decrease between 150 and 300 K. At the same time the emission peak position moved from ∼438 nm (20 K) to ∼412 nm (550 K). These data were explained as a result of a two-level emitting center with the higher state being thermally populated at the expense of the lower level.