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

Abstract

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 emission is observed at 260 nm. The same emission is also detected in the weakly cerium or terbium doped samples. This emission is probably due to self-trapped exciton (STE). It matches exactly the 4f → 5d absorption band of cerium ions leading to an efficient energy transfer. The nature of this transfer, radiative and/or non-radiative, is analysed. In terbium doped sample the 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.

Key Words:

• Cerium
• Terbium
• Self-trapped exciton
• Lanthanum phosphate