CORRELATION BETWEEN SPECTRA AND STRUCTURAL DATA OF YAG-TM3+ AND YAG-CR3+, TM3+

In order to elucidate the Stark structure of Tm3+ multiplets involved in the almost-equal-to 2 mum emission of YAG:Tm3+, and YAG:Cr3+, Tm3+, absorption and emission spectra have been measured over a wide range of concentrations. The Tm3+ spectra in YAG show, besides the main lines assigned to dodecahedral D2 sites, a set of satellites associated with Tm3+ in perturbed sites. An attempt to correlate Tm3+ spectra with YAG structure and structural defects has been made. Using our data and an improved algorithm we have been able to identify Stark levels of Tm3+ in D2 (Y3+) sites, especially in the F-3(4), H-3(4), F-3(3), and F-3(2) multiplets. The spectra due to Tm3+ in perturbed sites, with a lower symmetry, were used to assign levels corresponding to forbidden transitions in the D2 symmetry. Some of the identified levels in H-3(4) can explain the luminescence data and the cross-relaxation mechanism that lead to the population of the F-3(4) metastable level, while those in F-3(3) seem to play an important role in Cr3+-Tm3+ energy transfer. In Cr3+-codoped samples supplementary lines in both Cr3+ and Tm3+ spectra as well as a preferential energy transfer have been observed and explained in terms of structural data.