Solid state spectroscopy : laser spectroscopy of praseodymium doped mixed alkaline earth fluorides

Abstract

The defect centers formed in the double alkaline earth crystals Ca₁₋ₓSrₓF₂ : Pr⁳⁺ Cₐ₋ₓBaₓF₂:Pr⁳⁺, Sr₁₋ₓCaₓF₂ : Pr⁳⁺ and Sr₁₋ₓBaₓF₂ : Pr⁳⁺for x ＞ 0.02% , together with the deuterated versions of these crystals, were investigated using selective laser excitation. All crystals were doped with 0.01% Pr⁳⁺. The mixed crystal centers in these systems are derived from the prominent C₂ center in the parent CaF₂ : Pr⁳⁺ and Sr F₂ : Pr⁳⁺ crystals by the replacement of the host alkaline earth cations in the neighbourhood cation spheres of the Pr⁳⁺ ion by the dopant alkaline earth. Three fluorine centers for each of the Sr⁲⁺ and Ba⁲⁺ doped CaF₂ : Pr⁳⁺ crystals and two and one centers for the Ca⁲⁺ and Ba⁲⁺ doped SrF₂: Pr⁳⁺ crystals respectively were studied in detail. For the deuterated crystals, two centers were studied for each of the mixed crystal systems. From the total of 17 centers investigated, four common polarization characteristics were apparent and these were used to classify the centers as types A1, A2, A3 or A4. On the basis of the observed polarised fluorescence, the A1 and A2 centers are found to be consistent with having a Cs and C4v symmetry respectively and models were proposed for these centers accordingly. Ambiguities in the spectroscopic data prevented a presentation of definite models for the A3 and A4 centers. Temporal studies in the form of lifetime measurements were performed on these mixed crystal centers and crystal field trends from these studies are presented. Crystal field fits were attempted for some of the C4v centers. Though the results from the fits are tentative at the moment, problems and possible solutions are identified. The bleaching characteristics of the lower symmetry hydrogenic centers, known as bleaching centers, were studied. Results from the polarization studies here appear to support models previously assigned to the parent bleaching centers. The satellite centers associated with the parent bleaching centers are characterised and discussions of models for these centers are presented.