EPR and optical study of Yb³⁺-doped β-PbF₂single crystals and nanocrystals of glass-ceramics

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β-PbF 2 single crystals doped with YbF 3 (0.2% and 2%) were studied by x-ray diffraction (XRD), electron paramagnetic resonance (EPR) and optical spectroscopy. EPR revealed the presence of only one kind of paramagnetic ion Yb 3+ , in a cubic symmetry site. The optical absorption, emission and excitation spectra enabled us to identify the transitions attributed to Yb 3+ in the cubic site and to determine its energy level diagram. Site-selective laser spectroscopy also evidenced the presence of another type of Yb 3+ ions, undetectable by classical EPR. This second type, which dominates in the 2%-doped crystal and exhibits cooperative luminescence, was attributed to Yb 3+ ions forming clusters. Transparent oxyfluoride glass-ceramics, containing β-Pb 1− y Yb y F 2+ y nanocrystallites, were also synthesized and studied by XRD, EPR and optical spectroscopy. Two types of Yb 3+ ions were found, as in β-PbF 2 single crystals. The optical properties of the oxyfluoride glass-ceramics turn out to be similar to those of ytterbium activated β-PbF 2 single crystals. Moreover, the Yb environments found in PbF 2 single crystals seem to already occur in the parent glass. Therefore, these materials are expected to be good laser media, like the rare-earth doped fluorite crystals, either in bulk or fibre form.