Trends in Hamiltonian parameters determined by systematic analysis of f-d absorption spectra of divalent lanthanides in alkali-halides hosts: II. CaCl₂:Ln²⁺ (Ln = Sm, Eu, Tm, and Yb)

Systems containing divalent lanthanide elements (Ln²⁺) are hard to synthesize and thus their characterization is still largely an unexplored area. The absorption spectra of most divalent Ln²⁺ ions were, until recently, obtained nearly exclusively for Ln²⁺:CaF₂ crystals. In the first paper in a series devoted to systematic analysis of f-d absorption spectra of Ln²⁺ in alkali-halides hosts we presented new experimental data for Nd²⁺ and Dy²⁺ ions in SrCl₂ and reanalyzed available data for SrCl₂: Ln²⁺ (Ln = Sm, Eu, Tm, and Yb). The increased number of spectral data on the f-d transitions for Ln²⁺ ions makes SrCl₂ the second best studied matrix. The second paper in this series is devoted to CaCl₂:Ln²⁺ (Ln = Sm, Eu, Tm, and Yb). The first absorption, emission, and excitation spectra for Sm²⁺, Eu²⁺ and Yb²⁺ in CaCl₂ are reported. Using a uniform methodology based on a parametric Hamiltonian model proposed in Part I, a systematic analysis of the spectra is performed. This approach yields refined and consistent sets of the free-ion parameters and crystal-field (CF) ones. Systematic CF analysis of the large spectral dataset for CaCl₂:Ln²⁺ consisting of a total of four ions allows revealing inherent trends across the Ln series. Our results enable partial verification of the trends uncovered in Part I for Ln²⁺:SrF₂. It appears that the trends in the free-ion parameters and, to a lesser extent, CF ones observed for one Ln²⁺ ion are sufficiently systematic to allow for tentative predictions of the spectrum for any lanthanide ion based on the sets of parameters derived from the spectra obtained for another ion in the same matrix.