Exciton trapping in LaPO4 doped with trivalent cerium and/or terbium ions

Here, we present a study of exciton behaviour in LaPO4 doped with trivalent cerium and/or terbium ions. In undoped LaPO4 excited at 155 nm a weak emis sion is observed at 260 nm. The same emission is also detected in the weakl y cerium or terbium doped samples. This emission is probably due to self-tr apped exciton (STE). It matches exactly the 4f --> 5d absorption band of ce rium ions leading to an efficient energy transfer. The nature of this trans fer, radiative and/or non-radiative, is analysed. In terbium doped sample t he energy transfer from the STE exists but seems to be less efficient. This is essentially due to the fact that the STE emission overlaps terbium 4f - -> 4f transitions, the oscillator strengths of which are much weaker.