Study of TL glow curves of YPO _4 double doped with lanthanide ions (Conference Paper)

摘要

Thermoluminescence (TL) emission spectra and TL glow curves of samples of YPO _4:Ce ~(3+), Ln ~(3+) (Ln ~(3+) = Pr ~(3+), Nd ~(3+), Sm ~(3+), Dy ~(3+), Ho ~(3+), Er ~(3+), Tm ~(3+), Yb ~(3+)) and YPO _4:Tb ~(3+), Ln ~(3+) (Ln ~(3+) = Nd ~(3+), Ho ~(3+), Dy ~(3+), Sm ~(3+), Tm ~(3+)) were measured in order to investigate the nature of the trapping centres and to compare the lanthanide energy levels in the band gap with a predictive energy level scheme developed earlier. The nature of the trapping centres agrees with that predicted by the energy level scheme. The hole accepting dopants (Ce ~(3+) and Tb ~(3+)) act as recombination centres emitting the characteristic Ce ~(3+) or Tb ~(3+) emission. The electron accepting codopants produce glow peaks at different temperatures. The sequence of glow peaks maxima of the electron accepting codopants appears exactly as predicted by the level scheme of the divalent Ln ions. Trap depths, determined with the various heating rate method, follow the trend as predicted by the level scheme but were found systematically shallower. This can be explained by the uncertainty in the energy level predictions and/or tunnelling of the charge carriers from codopant to dopant and the presence of excited states of the divalent Ln ions in the band gap which makes alternative recombination pathways possible. In general it can be concluded that the energy level scheme is a powerful tool to interpret and predict all kinds of TL phenomena.