Study of the energy level scheme of Pr3+: LaOCl under pressure

Excitation and luminescence spectra of Pr3+ in LaOCl were measured over the spectral range from 11 000 cm(-1) to 22 000 cm(-1). At ambient pressure a total of 46 spectral lines could be observed. Under pressures up to 16 GPa, all lines exhibit a red-shift-however, with very different rates. From the spectral lines, the energy level scheme of the 4f(2) configuration could be partly derived. From 37 levels at ambient pressure, 30 could also be obtained under pressure. The energy level scheme is described by the use of free-ion (F-k (k = 2, 4, 6), alpha, beta, gamma, zeta) and crystal-field parameters (B-0(2), B-0(4), B-4(4), B-0(6), B-6(6)). According to the so-called nephelauxetic auxetic effect, the free-ion parameters F-k and zeta decrease under pressure. The magnitudes of the variations depend on the selected energy levels. Surprisingly the crystal-field strength shows a peculiar behaviour with an initial decrease and a minimum at 15 GPa. This behaviour can be explained within the context of the superposition model.