Experimental and theoretical investigation of the 4fn ⇆ 4fn-15d transitions in YPO4:Pr3+ and YPO4:Pr3+, Ce3+

Excited state absorption spectra from the 4f(2) levels of Pr3+ in YPO4 to 4f5d were measured at 293 and 77 K using a pulsed pump-probe technique. The spectra from the D-1(2) manifold were recorded by employing a continuous wave probe, whilst those from the P-3(J)-I-1(6) states were recorded by using for the first time a pulsed probe. These experimental results are compared with the numerical predictions of a full calculation of the 4f5d levels and the agreement is found to be good. A detailed study of the UV luminescence properties of the Pr3+ and the Ce3+ ions in the YPO4 host crystal, including the energy transfer between these two ions, is also reported. Fluorescence spectra and decay curves from the lower excited-state levels of the 4f5d and 5d electronic configurations of the Pr3+ and Ce3+ ions, respectively, were measured both at 293 and 77 K. The Pr3+ --> Ce3+ energy transfer efficiency was evaluated. Further considerations about the possibility to obtain laser emission based on the 5d --> 4f optical transition seem to indicate that this material is probably not a very good candidate to build a UV tunable laser because of a relatively short lifetime of the emitting level corresponding to a reduced quantum efficiency.