Energy transfer in pure and rare-earth doped SrAlF5 crystals

Abstract

This paper reports the results of investigation of luminescence and energy transfer processes in pure and Ce-, Gd- doped SrAlF5 single crystals by means of time-resolved UV-VUV and XUV luminescence spectroscopy. Reliable evidence of self-trapped exciton (STE) formation was found. The complexity of STE emission and excitation bands points to the presence of several non-equivalent sites where excitons can localize. At temperatures above ∼150 K the STE emission is quenched, probably due to higher mobility and increasing probability of their interaction with defects. The role of the energy transfer of Ce3+ ions with lattice defects at different temperatures is discussed. For Gd3+:SrAlF5 crystal no effective direct excitation of the characteristic 3.97 eV Gd3+ emission was found. Instead, a new PL band at 5.6 eV was revealed, which can be excited through 8S7/2 - 6G transitions in the 4f7 configuration of Gd3+. This phenomenon is tentatively explained by high probability of energy transfer from gadolinium to nearby defects. However, efficient excitation of the characteristic Gd3+ emission in the range of 7-11 eV points to resonant energy transfer from growth defects to the dopants in the same manner as proposed for Ce3+, and this process populates directly the 6P7/2 level of Gd3+ from which emission takes place. © 2010 IOP Publishing Ltd.