Ab initio theoretical study on the 4f(2) and 4f5d electronic manifolds of cubic defects in CaF2:Pr3+

Wave function-based embedded cluster ab initio calculations have been carried out in order to study the 4f(2) and 4f5d energy levels of the cubic substitutional defect of Pr-doped CaF2. The 4f(2) → 4f5d absorption spectrum and 4f5d → 4f(2) emission spectrum have been calculated. The 4f(2 1)S0 level is found to be immersed in the 4f5d(eg) manifold, so that no quantum cutting from (1)S0 can occur and only strong 4f5d(eg) → 4f(2) emission is predicted, which supports previous assumptions made in order to explain results in CaF2:Pr(3+). The details of the 4f(2) → 4f5d(eg) and 4f(2) → 4f5d(t2g) bands of the absorption spectrum are interpreted and assignments are made. The lowest level of the 4f5d(eg) configuration is found to have 80% of singlet character, in opposition to Hund's Rules, and the issue is discussed in detail. The comparison between the experimental 4f5d(eg) → 4f(2) high resolution emission spectrum of the cubic site of CaF2:Pr(3+) and the calculated emission spectra from the two lowest 4f5d(eg) states 1T2u((1)T2u) and 1Eu(1(3)T2u) suggests the possibility that the experimental emission of the cubic Pr defect of CaF2:Pr(3+) is in fact a multiple emission.