Thermoluminescence and Kinetics of Persistent Luminescence of Vacuum-Sintered Tb3+-Doped and Tb3+,Ca2+-Codoped Lu2O3 Materials

The properties of green thermoluminescence (TL) and persistent luminescence of Lu2O3:Tb3+ and Lu2O3:Tb3+,Ca2+ materials sintered in vacuum at 1700 °C were investigated. The concentration of Tb varied in the range 0.1–3 mol %, and the Ca content was 1 mol %. Ca2+ codoping enhanced the room temperature persistent luminescence intensity and its duration as well as reduced the number of TL bands for lightly doped materials from four components covering about 50–400 °C range of temperatures to only one peaking around 100 °C. The Tb3+,Ca2+ (0.1 and 1 mol %, respectively) codoped material showed the most efficient persistent luminescence and TL, originating mainly from the 5D4 → 7F5 transition at around 545 nm, among all the compositions investigated. For this material the persistent luminescence could be observed in the dark for about 15 h. There are indications that the efficient persistent luminescence of the codoped system is governed by tunneling mechanism, and the trapping centers are postulated to be [TbLu×−VO••−2CaLuˈ] aggregates. Oxygen vacancies are supposed to serve as traps for free electrons giving F+ (eO••) or F (VO×) centers while holes are temporarily immobilized in the vicinity of TbLu× giving [TbLu×−h•] entities. Alternatively, hole can be trapped in the CaLuˈ site due to its negative net charge, giving [CaLuˈ−h•]. Air-sintered specimens did not show any significant persistent luminescence or TL, although they produce quite significant photoluminescence. Also, vacuum sintering at lower temperatures—1600 °C and below—was not sufficient to get efficient persistent luminescence.