Polarized Optical Absorption Spectrum of Ho3+ in HoCl3· 6H2O

The optical absorption spectrum of Ho³⁺ in single crystals of ${\mathrm{HoCl}}_3\text{· 6}{\mathrm{H}}_2\mathrm{O}$ has been investigated at 4.2°K between 2500 and 9000 Å. Polarization studies have been carried out on most spectroscopic groups in the region between 3200 and 9000 Å. The far‐infrared spectrum, reported between 30 and 400 cm⁻¹ at room temperature, made it possible to distinguish between the optically observed vibronic and electronic (zero‐phonon) spectra. The observed centers of gravity of the 4f¹⁰[SL]‐J levels of Ho³⁺ are compared to those calculated previously for Ho³⁺ in LaCl₃.