Electronic spectra of Yb2+-doped SrCl2.

The absorption and emission spectra of Yb(2+)-doped SrCl(2) have been calculated on the basis of ab initio quantum chemical calculations which consider recently found, unexpected excited states with double-well energy curves and complex electronic structure, resulting from avoided crossings between Yb-trapped excitons and Yb impurity states, which influence prominent spectral features. The root mean square deviation and largest absolute error of the calculated energy levels are 394 and -826 cm(-1), respectively. The YbCl(8) moiety breathing mode vibrational frequencies and bond lengths of the lowest states are consistent with observed vibrational progressions and energy shifts induced by uniaxial compression. Photoionization is predicted above 49,000 cm(-1) as a consequence of the spin-orbit induced spreading of the Yb-trapped exciton character in the upper part of the spectrum and three new emission bands are predicted with origins at about 33,800, 36,400, and 43,600 cm(-1). The electron correlation methods used overestimate the relative stabilization of the 4f(14) ground state and this leads to a constant error of the whole absorption spectrum of about 3500 cm(-1) (23%-7%). Although this energy shift is customarily considered an adjustable parameter, it is a nonparametric, direct product in an ab initio route which shows the limitations on the proper representation of differential correlation between the 4f(N) and 4f(N-1)5d (or similar) configurations and the need for theoretical improvement.