Optical spectroscopy study of KDy(WO₄)₂: Crystal-field levels of Dy³⁺ and the Jahn–Teller transition

Transmission spectra of a double potassium-dysprosium tungstate KDy(WO₄)₂ single crystal in the region of intermultiplet transitions of the Dy₃⁺ ion and the Raman spectra of light scattering on the electronic levels of the ⁶ H_15/2 ground multiplet of Dy³⁺ are studied in a wide temperature range. The energy scheme for the crystal-field (CF) levels of Dy³⁺ in KDy(WO₄)₂ is created. The phase transition at the temperature 6.3 K is accompanied by the lowering of the energy of the ground Dy³⁺ CF state, which is evidenced by both the transmission and Raman spectroscopies. Splitting of the low-lying (~13 cm^–1 ) first excited CF level of the Dy³⁺ ion indicates the simultaneous structural phase transition. The role of Davydov interaction is discussed. (author)