Systematic analysis of the optical spectra of selected RE3+ ions in rare-earth oxyfluoride

Abstract

The c.f. structure of the2S+1LJ levels of the Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, and Dy3+ ions in hexagonal rare-earth oxyfluoride (REOF) matrices was derived from an analysis of the optical absorption, luminescence, excitation, and inelastic neutron-scattering spectra. The energy-level schemes were simulated with a phenomenological model which included the parametrized electrostatic (the Racah parameters E0–3) and the two- and three-body configuration interactions (Tree's parameters α, β, and γ as well as Judd's parameters Tk) as well as spin-orbit coupling (the coupling constant ζ4f). The effect of the neighboring ions was taken into account by a crystal field of C3v symmetry. All parameter values were determined unambiguously by least-squares calculations by considering simultaneously both the free-ion and c.f. interactions. The standard deviations achieved in some simulations were low, considering the restricted degrees of freedom due to the limited basis set of experimentally observed levels. The B q k parameters were found to evolve smoothly across the RE3+ series. For the lighter RE3+ ions the shifts in the c.f. parameter values correlated well with the model emphasizing the effect of the increasing nuclear charge, whereas beyond Tb3+ additional effects may be needed to describe the evolution of the B q k values. Further work is hence needed for the heavier RE3+ ions in RE-oxyfluoride hosts in order to assess the importance of, e.g., the two-electron c.f. interactions and the correlation between the c.f. effect and the crystal structure.