Vibrational structure in optical spectra of the Ca 4GdO(BO 3) 3 (GdCOB) single crystal doped with Re 3+ (Eu, Tb, Yb)

Abstract

The optical spectra of compounds containing trivalent rare earth (Re 3+) ions often show vibronic features. The intensity of vibronic transitions is determined by the strength of the electron–phonon (ion–lattice) coupling and depends strongly on the rare earth and the host lattice. In this paper we report on electron–phonon coupling in the GdCOB system doped with Eu 3+, Tb 3+ and Yb 3+ ions. According to general theory intense vibronic lines are to be expected for electronic transitions with Δ J=0, ±2 and these transitions were mainly considered in this paper for both Eu 3+ and Tb 3+ ions. In the case of Yb 3+ ions, a strong vibronic sideband belongs to the 2F 7/2→ 2F 5/2 transition with Δ J=1 although it seems to be in contradiction to the general selection rule. The vibronic features observed in absorption, excitation and emission spectra were analysed on the basis of the host lattice modes obtained from Raman and the far infrared spectra of the matrix.