Polarized absorption spectra of the Nd³⁺ ion in the optically active Na₃Gd (diglycolate)₃·2NaClO₄·6H₂O single crystal

Abstract

The polarized absorption spectra of the Nd³⁺ ion in optically active single crystals of Na₃Gd(diglycolate)₃·2NaClO₄·6H₂O have been measured in the 875-350 nm spectral range over the temperature range from 4 to 300 K using spectrographic and spectrophotometric methods. Pulsed Zeeman measurements of selected spectral regions have also been performed. Analysis of the data has led to the location and assignment of the crystal quantum number, µ, associated with the ⁴I_9/2 ground state crystal field levels. They lie at 0 cm^-1 (μ=1/2), 20 cm^-1 (μ=3/2), 135 cm^-1 (μ=1/2), 320 cm^-1 (μ=1/2) and 450 cm^-1 (μ=3 The location and assignment of excited state multiplets and their crystal field (CF) μ levels have also been accomplished. Eleven separate excited multiplets and their thirty-seven associated CF levels have been assigned. Four overlapping or broad multiplet combinations have been identified, but the μ-level assignments have only been possible in those cases involving multiplets with low J values (< 9/2). For the multiplets with J > 9/2 only the locations of the CF levels could be determined. The low-temperature phase transition during which the site symmetry is lowered from D₃ to C₂ is shown to affect the polarization behavior of the multiplets of high J value to a significantly greater extent than those of low J value. This is attributed to intra- and inter-multiplet μ-level mixing by the low-symmetry crystalline field.