Spectra and energy levels of Nd3+(4f3) in stoichiometric NdP5O14

We report a detailed crystal-field splitting analysis of the 13 lowest-energy multiplet manifolds, ^2S+1L_J, of Nd³⁺(4f³) in stoichiometric NdP₅O₁₄. The observed manifold splittings were determined by analyzing the absorption spectra between 550 and 1750 nm and the fluorescence spectra between 800 and 1400 nm at temperatures between 8 K and room temperature. The spectra are remarkably sharp given the high concentration of Nd (28.91 wt%) in the stoichiometric crystal. The number of transitions to and from individual multiplet manifolds is consistent with Nd³⁺ ions occupying sites, reported earlier to be of low symmetry (C₁). Sixty experimental energy (Stark) levels associated with the 13 manifolds are compared to a crystal-field splitting calculation in which the observed-to-calculated rms deviation is 6.8 cm⁻¹.     

High and low spin energy states of the Tb 4f5d configuration in BaF2

In this paper we present results of detailed spectroscopic studies of Tb³⁺ luminescence from BaF₂:0.075 mol% Tb performed at Superlumi station of Hasylab, DESY, Hamburg and at Institute of Physics, N. Copernicus University, Torun, Poland (IF UMK Torun).We have measured UV/VUV excitation spectra of the dominant blue Tb³⁺ luminescence and emission spectra under excitation into various bands found from the excitation spectra. The excitation spectra are dominated by the two well known broad bands due to the parity and spin-allowed (SA) 4f⁸ → 4f⁷5d transitions. The higher energy triple t-band and unresolved single e-band at lower energies are widely separated (10 Dq about 16,500 cm⁻¹) reflecting the single d-electron energy in the high symmetry cubic crystal field with a relatively low contribution from the low symmetry component.In addition to these bands we have also detected a number of weaker bands at lower energy sides of both dominant SA bands. While the structured band with components at 252.8, 252.3, 250.4 and 248.4 nm clearly corresponds to the SF (spin-forbidden) band found earlier in LiYF₄:Tb, the bands at 183, 178 and 172 nm have been never, to the best of our knowledge, reported before. We present arguments that these new bands are the SF counterparts of the triple SA t-band at about 158 nm. The d-f exchange energies for d(e) and d(t) electrons are different at 7779 and 8245 cm⁻¹, respectively.Although the energy levels corresponding to the identified high and low spin (HS and LS) states of the 4f⁷5d configuration are, in BaF₂, well separated, there are no SA nor SF transitions generating d-f emission in BaF₂:Tb. This is because the numerous 4f⁸ energy levels intercept the excitation energy from 4f⁷5d levels leading to the well known blue and green Tb³⁺ 4f⁸ emissions.