A new photoluminescent feature in LuPO4:Eu thermoluminescent sintered materials

Nanocrystalline powders of LuPO4:Eu were prepared at 230 degrees C by a hydrothermal method. Their post-treatment at 900, 1200 and 1350 degrees C induced a moderate grain growth from similar to 20-50 nm up to 80-300 nm. These powders were sintered at 1700 degrees 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 degrees C. The photoluminescence characteristics of the broad luminescence was performed in the 20550 K range of temperature. While the intensity of this emission did not change within 20-550 K its decay time dropped from similar to 823 mu s (20 K) to similar to 7 mu s only (550 K) with the most potent decrease between 150 and 300 K. At the same time the emission peak position moved from similar to 438 nm (20 K) to similar 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.