EPR and optical studies of erbium-doped β-PbF2 single-crystals and nanocrystals in transparent glass–ceramics

Abstract

β-PbF₂ single-crystals and nanocrystals in transparent glass–ceramics doped with ErF₃ have been synthesized and studied with two complementary techniques: electron paramagnetic resonance (EPR) and optical spectroscopy (absorption, selective excitation, fluorescence). A comparative study shows that, in both single-crystals and glass–ceramics, Er³⁺ ions occupy the same types of sites, leading to similar optical properties. An EPR investigation demonstrates that, in these materials, part of the Er³⁺ ions occupy cubic symmetry sites. For these ions, we determine the crystal field splitting of the ground state ⁴I_15/2 and the symmetry of its sublevels. We also provide evidence for the presence of another type of Er³⁺ ions, not detectable by EPR but evidenced by optical spectroscopy. We clearly show that this Er³⁺, which gives rise to up-conversion luminescence, corresponds to clusters associating Er³⁺ and F⁻ ions. In the single-crystals, the proportion of these two types of erbium ions is estimated. It strongly depends on the doping rate of the β-PbF₂ crystals.