Site-selective spectroscopy of Pr³⁺ ions in sodium [MATH]-alumina crystals

Abstract
We report on the results of a low-temperature optical spectroscopy study of Pr³⁺-exchanged sodium β-alumina single crystals (Na⁺/Pr³⁺ β-Al₂O₃), containing different amounts of luminescent ions, in which excitation and fluorescence spectra have been carried out in σ and π polarization. The ³P₀ → ³H₄ emission spectra, obtained under broad band excitation, show an intriguing structure consisting of several components even with crystals containing low Pr³⁺ concentrations. The excitation spectra indicate the presence of at least two sets of different sites, available to Pr³⁺ in the conduction plane of [MATH]-alumina. Independently of the crystal composition, a quite satisfactory site-selective emission from each sets of centres has been achieved under cw excitation of the 465.8 nm and 476.5 nm lines of an Ar⁺ ion laser.