High-resolution spectroscopy of a YVO4:Ho3+single crystal: Resolved hyperfine structure and potential for cryothermometry

The paper reports the first observation of a resolved hyperfine structure in the optical spectra of YVO4:Ho3+ crystal and discusses its possible applications in the remote thermometry. The transmission spectra of YVO4:Ho3+ in the region of 5I6 and 5I7 multiplets of the Ho3+ ion at low temperatures were investigated. The energies and symmetries of crystal-field (CF) levels of these multiplets have been refined. The hyperfine structure was observed for optical transitions from the Gamma 5 CF level at 46.9 cm -1 of the ground multiplet. Deformation splittings were observed for several Gamma 5 states, which can be used for crystal quality control. Magnetic g factors were derived for the Gamma 5 levels. The YVO4:Ho3+ material can be used as a working medium for thermometry over a wide temperature range from two to several hundred Kelvin.