Aspects of solid-state rare-earth and hydride-ion-vibrational spectroscopy have been studied, using the techniques of laser-selective excitation, infrared absorption and Zeeman spectroscopy. The calcium-fluoride family of host crystals form, in many respects, a model system with a well characterised cubic lattice and their ready acceptance of a variety of dopant ions.

A laser-selective excitation study of single-Tm³⁺ ion centres in CaF2 has identified two main centres, having C4v and C3v symmetry respectively, while a third centre of cubic symmetry has been identified through infrared-absorption and Zeeman spectroscopy. In deuterated CaF2:Tm³⁺ crystals, four Tm3+ centres involving D-ions have been studied, with three of these centres exhibiting reversible polarised bleaching.

Several instances of upconversion fluorescence arising from single-ion centres in CaF2:RE³⁺ have been observed for single-laser excitation. The upconversion mechanism has been shown to be a sequential-absorption process, with the laser tuned to resonance with one of the two sequential electronic transitions. A novel enhancement by two orders of magnitude of a particular red-to-blue upconversion fluorescence in CaF2:Tm³⁺ has been observed upon warming the sample from 15 K to room temperature.

The doubly-degenerate transverse vibrational mode of the H- ion in the C4v site adjacent to a RE³⁺ ion can be split due to coupling of the vibrational modes with the RE³⁺ ion electronic states. The magnitude of these splittings is dependent on the specific rare-earth ion present; these splittings have been measured and compared with the results of calculations based on a point-charge model of the crystal-field potential.

Further splittings of these vibrational modes upon the application of external magnetic fields have been measured. These splittings are well accounted for by a firstorder perturbation matrix involving the electronic Zeeman effect and measured zerofield splittings.