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.