Optical spectra and thermal Schottky levels in dysprosium sesquisulfide

摘要

We report a detailed crystal-field splitting analysis of the energy levels of Dy~(3+) (4f~9) in single crystals of Dy_2S_3 that have the Th_3P_4 cubic defect structure. From an analysis of the temperature-dependent absorption spectra, we have identified seven of the eight crystal-field split energy (Stark) levels of the ground-state multiplet manifold, ~6H_(15/2). Sixty-two experimental Stark levels from various multiplet manifolds of Dy~(3+) are compared with a calculated crystal-field splitting, whose initial crystal-field parameters, B_(nm), were determined from lattice-sum calculations. The rms deviation between experimental and calculated levels is 7 cm~(-1). Both the experimental and calculated crystal-field splitting of the ~6H_(15/2) manifold are compared with an assignment of Schottky levels obtained from a reassessment of heat capacity data reported earlier. Based on entropy considerations and verification of the Schottky level assignments by analyses of the optical and magnetic susceptibility data, we conclude that the anomaly observed in the heat capacity data near 3.4 K is due to antiferromagnetic ordering.