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

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 line s assigned to dodecahedral D2 sites, a set of satellites associated wi th 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 T m3+ 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 l ower symmetry, were used to assign levels corresponding to forbidden t ransitions 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 thos e in F-3(3) seem to play an important role in Cr3+-Tm3+ energy transfe r. In Cr3+-codoped samples supplementary lines in both Cr3+ and Tm3+ s pectra as well as a preferential energy transfer have been observed an d explained in terms of structural data.