Excitation and luminescence spectra of in LaOCl were measured over the spectral range from to . 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 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 ( (k = 2, 4, 6), ) and crystal-field parameters . According to the so-called nephelauxetic effect, the free-ion parameters and 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.

Fluorescence and absorption spectra of Pr 3ϩ :PrOCl (PrPr) were measured in the range from 11 500 cm Ϫ1 to 22 500 cm Ϫ1 under pressures up to 16 GPa. From these spectra, the pressure dependence of the energy-level scheme of the 4 f 2 configuration of Pr 3ϩ could be partly derived. The effect of pressure on the free-ion parameters F 2 , F 4 , F 6 , and was determined and compared in detail with former results on Pr 3ϩ :LaOCl (PrLa) and Pr 3ϩ :GdOCl (PrGd). The observed shifts can be described by a combination of central-field and symmetry-restricted covalency in all cases. The variations of the crystal-field parameters are analyzed in the framework of the superposition model. Although specific features can be accounted for by this model, distinct deviations reveal the difficulties in applying this model to compounds with two different ligands.

Excitation and luminescence spectra of Pr 3+ in GdOCl were measured in the spectral range from 11 000 cm −1 to 22 500 cm −1 . At ambient pressure a total of 54 spectral lines were observed. Some of these lines cannot be explained by transitions between crystal-field levels of the regular Pr 3+ site in GdOCl. Possible explanations of these lines are discussed. Under pressure up to 16 GPa, all lines exhibit a red-shift, from which a part of the energy level scheme of the 4f 2 configuration could be derived. From the 34 levels at ambient pressure, 31 could also be obtained under pressure. The energy level scheme is described in terms of the free-ion parameters (F k , α, β, γ , ζ , M k , P k ) and crystal-field parameters (B 2 0 , B 4 0 , B 4 4 , B 6 0 , B 6 6 ). The variations of these parameters under pressure were determined. Surprisingly, the crystal-field strength, calculated from the crystal-field parameters, first shows a slight decrease with increasing pressure.