Laser selective excitation of praseodymium ions in hydrogenated fluorite crystals
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The techniques of laser selective excitation have been successfully applied to study the multitude of spectroscopic sites present in hydrogenated SrF₂:Prᶾ⁺and CaF₂:Prᶾ⁺ crystals. Many optical transitions of the tetragonally sited Prᶾ⁺ions have been characterised using well defined polarisation rules, and comprehensive sets of energy levels have been established. For the hydrogenic C₄ᵥ Prᶾ⁺sites, the predictions of a single frequency multiphonon relaxation theory show excellent agreement with the results of a temporal study of these sites. The results show that the relaxation of the Prᶾ⁺electronic system is entirely determined by the hydrogenic ion local mode phonons. Several low symmetry hydrogenic Prᶾ⁺centres show the, new to inorganics, property of reversible bleaching. Two mechanisms have been identified, where a photoproduct is formed with a different site orientation or at a different excitation wavelength. Site configurations have been developed that successfully account for many of the observed bleaching effects.