Optical spectra and crystal field analysis of Dy3+ in Cs2NaDyCl6 and Cs2NaYCl6: Dy3+(5 mol %)

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Abstract
Optical absorption and emission measurements are reported for the Cs2NaDyCl6 and Cs2NaYCl6: Dy3+(5 mol %) systems under variable‐temperature (10–298 K) conditions. For both systems, the data are compatible with the retention of octahedral (Oh) site symmetry at the Dy3+ ions over the entire 298 to 10 K temperature range. The only differentiation between the systems is the much greater quantum efficiency of 4F9/2 emission in the doped system vs that in the neat system. Forty‐five crystal‐field levels spanning 18 multiplets of the Dy3+ 4f9 electronic configuration are located and assigned, and an additional 12 crystal‐field levels associated with six other multiplet manifolds are located, but left unassigned. These energy level results are analyzed on the basis of a nine‐parameter 4f‐electron Hamiltonian operating within a complete Russell–Saunders (SLJ) basis set for the 4f9 configuration of Dy3+. The most intense electric‐dipole vibronic lines observed in the optical spectra are assigned to one‐phonon vibronic transitions associated with the three odd‐parity ‘‘moiety’’ modes of the DyCl3−6 octahedral clusters: ν3(t1u), ν4(t1u), and ν6(t2u). Intensity calculations are reported for both the no‐phonon magnetic‐dipole (origin) transitions and the one‐phonon (ν3, ν4, and ν6) electric‐dipole vibronic transitions.