The polarized optical absorption and fluorescence of Pr3+ in crystals were investigated at low temperatures in order to characterize the crystal field energy levels for every multiplet of the system. Up to 51 energy levels were determined for this ion, and were labelled by irreducible representations; assuming C3 local symmetry. These energy levels were used to estimate the crystal field (Bqk parameters) which acted on the Pr3+ ion in this host. As the optical spectra exhibited an additional structure which was due to the presence of four Pr3+ centres, laser site-selective spectroscopy was used to determine the Stark sub-levels of the 3H4 ground state for each particular centre. Thus, slight variations in the Bqk parameters, from centre to centre, were interpreted in terms of various Li+ off-centre positions for Pr3+ ions.

Crystal Field and Energy Levels of Pr3+ Centres in LiNbO3. J.E.Muñoz-Santiuste, A.Lorenzo, L.E.Bausá, J.G.Solé: Journal of Physics - Condensed Matter, 1998, 10[34], 7653-64