Experimental and theoretical investigation of the 4f(n) <-> 4f(n-1)5d transitions in YPO4 : Pr3+ and YPO4 : Pr3+, Ce3+

Excited state absorption spectra from the 4f(2) levels of Pr3+ in YPO4 to 4 f5d 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 wa ve 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 an d the agreement is found to be good. A detailed study of the UV luminescenc e properties of the Pr3+ and the Ce3+ ions in the YPO4 host crystal, includ ing the energy transfer between these two ions, is also reported. Fluoresce nce spectra and decay curves from the lower excited-state levels of the 4f5 d and 5d electronic configurations of the Pr3+ and Ce3+ ions, respectively, were measured both at 293 and 77 K. The Pr3+ --> Ce3+ energy transfer effi ciency was evaluated. Further considerations about the possibility to obtai n 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 tun able laser because of a relatively short lifetime of the emitting level cor responding to a reduced quantum efficiency.