Lanthanide energy levels in YPO4

Thermoluminescence (TL) emission spectra and TL glow curves of powder samples of YPO4:Ce3+, Ln(3+) (Ln(3+) = Nd3+, Sm3+, Dy3+, Ho3+, Er3+, Tm3+) were measured in order to investigate the nature of the trapping centres and to locate the lanthanide energy levels relative to the valence and conduction bands of the YPO4 host. Trap depths were determined by three different TL techniques (simple formula, various heating rate method and glow curve fitting) and compared with an earlier developed predictive energy level scheme. The nature of the trapping centres agrees with that predicted by the energy level scheme. Further, the trend of trap depths of the divalent lanthanides (Ln(2+) = Nd2+, Sm2+, Dy2+, Ho2+, Er2+, Tm2+) agrees very well with the trend of levels determined by three different thermoluminescent techniques. It is concluded that the energy level scheme can help in the development of new TL materials suitable in dosimetry. (C) 2007 Elsevier Ltd. All rights reserved.