Crystal fields of Pr3+ in LiYF4 under pressure

Fluorescence spectra of LiYF4:Pr3+ have been measured between 12,000 and 22,000 cm−1 under pressures up to 10 GPa. In total, 25 crystal field energy levels were obtained and used for the determination of free-ion and crystal field parameters under pressure. According to the nephelauxetic effect, the free-ion parameters decrease with increasing pressure. The relative decrease is larger for the Slater than for the spin–orbit coupling parameter. This behavior is consistent with former studies on Pr3+ in different crystals and can be explained by a special covalency model. According to an effective D2d symmetry, five crystal field parameters B02(f,f), B04(f,f), B44(f,f), B06(f,f), and B46(f,f) are non-zero. The pressure-induced changes of these parameters have been determined up to the maximum pressure of 10 GPa. In order to improve the calculation of the crystal field levels, the configuration interactions with the 4f16p1 configuration have been taken into account. The effect of these interactions are also analyzed under pressure and distinct improvements of the energy level calculations have been obtained.