Andris Antuzevics defend PhD thesis "Local Structure of s-State Rare Earth Ions in Fluorides and Oxyfluoride Glass Ceramics"

In this work local structure of S-state rare earth ions (Gd³⁺ and Eu²⁺) is investigated with electron paramagnetic resonance (EPR) spectroscopy technique in ScF₃ and BaY₂F₈ single crystals as well as in oxyfluoride glass ceramics containing MeF₂ (Me = Ca, Ba, Sr) crystallites. EPR spectra parameters at different temperatures for gadolinium in ScF₃ – crystal with negative thermal expansion coefficient – indicate a positive expansion of the centre local structure with temperature. The Gd³⁺ centre of BaY₂F₈ crystal can be described with a set of low symmetry EPR spectra parameters. As S-state ions embed the crystalline phase of oxyfluoride glass ceramics, the glassy U-type spectrum is superimposed by an intensive EPR spectra fine structure at g = 1.99. Good agreement between the experimental and simulated spectra can be achieved by taking the defect centre parameters of the corresponding single crystals. EPR spectra of glass ceramics with europium contain information about the valence state of ions as well as Eu²⁺ local structure.