Ab initio embedded cluster study of the excitation spectrum and Stokes shifts of Y2O3 doped by Bi^3+
Résumé
The ab initio embedded cluster method coupled with correlated spin-orbit calculations has been used to interpret the excitation spectrum of a Bi3+-doped yttria crystal. Our results indicate that the Bi3+ impurity can absorb light over a wider energy range in the C2 site than in the S6 site. Even if the computed absorption energies seem to be about 0.4 eV too high with respect to the experimental peaks for both sites, it is noteworthy that the embedded cluster model renders 93% of the large crystal redshift, about 6 eV. The determination of the geometry relaxation of the first shell of oxygen neighbors upon electronic excitation shows that the Stokes shift is smaller in the S6 site than in the C2 site. Combining all these results confirms the assignment of the violet emission to the S6 site and that of the green emission to the C2 site, as proposed by Boulon