Pierre Porcher

Free ion and crystal field parameters for REOCl : Eu3+

The fluorescence spectra of Eu3+ activated rare earth oxychlorides REOCl : Eu3+ (RE = Y, La, Gd) were recorded and analyzed at 4.2, 77, and 300 K. For each compound more than 100 transitions between the Stark levels of the 4f6 configuration were observed and assigned. The energy level schemes established from the spectra show a relatively strong crystal field effect. The five nonzero crystal field parameters for the C4v point site symmetry occupied by the rare earth ion were determined, yielding a mean square deviation of a few cm−1. The free‐ion parameters were also determined with the aid of excitation spectra. The effect of truncation of the basis set of the 2S+1LJ levels on the energy level simulation of the excited levels was also studied.

Relationship between phenomenological crystal field parameters and the crystal structure: The simple overlap model

The simple overlap model is used to calculate crystal field parameters from the crystal structure. It is applied to 25 rare earth and some actinide and 3d transition element compounds for which crystal field parameters have been previously determined experimentally. The model is based on effective charges, located around the middle of the rare earth ion–ligand distance, which are assumed to be proportional to the magnitude of the overlap, ρ, between the rare earth ion and ligand wavefunctions. Good agreement between theoretical and experimental crystal field parameters is found for most of the cases studied. The best predictions are obtained when the overlap varies slightly from one rare earth compound to another (0.05<ρ<0.08), in agreement with the general assumption that the f orbitals have a small part in the chemical bonding. For the two examples involving the 5f elements, the overlaps with the ligand have, curiously, the same magnitude as in the case of the rare earth elements. As expected, the 3d element wavefunctions show a stronger mixing with those of the ligands (0.10<ρ<0.25).

Influence of J-mixing on the phenomenological interpretation of the Eu3+ ion spectroscopic properties

Abstract Two sets of Bkq crystal field parameters and Bγkq intensity parameters have been calculated from the transition occuring between the Stark levels of Eu3+ in KY3F10. One of the calculations includes the J-mixing; the other not. The influence of the J-mixing on the intensities of the “forbidden” transition 5D0 → 7F0 and on the hypersensitive transitions are analysed.

Crystal field parameters for Eu3+ in KY3F10

The fluorescence spectrum of KY3F10: 1% Eu in powder form was recorded at 77 and 4.2°K between 4600 and 7000 A, and 89 fluorescence lines arising from levels 5D0, 5D1, 5D2, and probably 5D3 were observed. The spectrum agrees with with a C4v symmetry, and it is possible to determine the irreducible representation of the group associated with the Stark components of 2S+1LJ levels. The set of crystal field parameters agreeing best with the experiment, on a basis of 200 kets ‖7F≳, ‖5D≳, and ‖5G≳ of the 4f6 configuration, is B20=−551 cm−1, B04=−1360 cm−1, B44=+345 cm−1, B60=394 cm−1, and B64=234 cm−1.

Crystal field effects in REOBr:Eu3+

Crystal field parameters (Bkq) were obtained for the REOBr:Eu3+ series (RE = Y, La, Gd) and LaOI:Eu3+ from the analysis of fluorescence spectra. The sets of five nonzero Bkq parameters for the C4v symmetry reproduce the experimental 7FJ Stark level schemes within a few cm−1. The Racah (E0–3) and spin–orbit (ζ) parameters were determined for the REOBr:Eu3+ series with the aid of excitation spectra. Only insignificant shifts were observed in the parameter values along the series. A simulation of the Stark level sequences of excited levels was carried out on a strongly reduced basis set of 2S+LLJM levels. A poor simulation was obtained unless the free‐ion wave functions were well defined. A comparison of the crystal field parameters for the whole REOX:Eu3+ series (RE = Y,La,Gd; X = Cl, Br,I) shows an increase in the strength of the crystal field with increasing ionic radius of the RE3+ host cation. A similar pattern prevails in the oxyhalide series from the oxychloride to the oxybromide host. The crystal fie...

Energy levels of Nd3+ in LiYF4

High‐resolution absorption spectra of Nd3+ in LiYF4 were recorded between 3900 and 40 200 cm−1 at temperatures from 10 to 300 K. The levels were obtained by diagonalizing a Hamiltonian that describes the free ion parameters, including two and three‐body configuration interactions, as well as the crystal field operator. Calculations were performed using the complete basis of 364 ‖αSLJMj〉 kets of the 4f3 configuration of Nd3+. A set of free ion and crystal field parameters were calculated which fitted energy levels with an rms deviation of 22 cm−1 with respect to 134 experimentally determined levels.

Preparation and optical properties of europium-activated rare earth oxysulfates

Abstract The rare earth oxysulfate series Ln2O2SO4 (Ln = La, Gd, Y) was synthesized by two different thermal decomposition methods. The complex ion (LnO)n+n existing in the structure of various oxysalts seems to have a major effect on the appearance of the spectra. Then it is possible to derive sets of crystal field parameters simulating the spectra, by using the C4ν → C2ν descending symmetry procedure. Moreover, an alternative method for determining these parameters is described when a C2ν point site symmetry is distorted from D3h.

Optical spectroscopy of Pr3+ in KGd(WO4)2 single crystals

The polarized optical absorption (OA) and photoluminescence of Pr3+ doped KGd(WO4)2 (KGW) single crystals have been measured at selected temperatures between 7 and 300 K. For the studied Pr concentrations, [Pr] = 0.03×1020-1.9×1020 cm-3, a unique site is observed. 74 energy levels were experimentally determined for this site and labelled with the appropriate A or B irreducible representations corresponding to the C2 symmetry of the Gd point site in KGW. The set was fitted to a Hamiltonian of adjustable parameters including free-ion as well as real Bqk and complex Sqk crystal-field parameters. A good simulation of the experimental crystal field energies was achieved with a root mean square deviation σ = 15.3 cm-1. Distortions in the oxygen bonds to Pr3+ are found to contribute to the broadening of some OA bands, particularly those related to the 1D2 multiplet. The OA edge is determined by the interconfigurational 4f→4f15d1 Pr3+ transition peaking at 34 200 cm-1. From the average 300 K OA cross sections the radiative lifetimes of the Pr3+ multiplets have been calculated considering the standard and modified Judd-Ofelt (JO) theories. A better agreement with the experimental results is obtained by the standard theory: the average JO parameters obtained at 2 = 12.0×10-20 cm2, 4 = 8.15×10-20 cm2 and 6 = 2.64×10-20 cm2. Electrons excited to the 3P0 multiplet decay very efficiently to the 1D2 multiplet even at 15 K. In samples with [Pr]≥0.3×1020 cm-3 the excitation of the 1D2 multiplet decays non-radiatively by an electric dipole-dipole transfer between Pr neighbours.

Spectroscopic properties of Ln2MoO6:Eu3+

The spectroscopic properties of Ln2MoO6:Eu3+ (Ln = La, Gd, Y) compounds were investigated. The differences in the recorded fluorescence spectra are in accord with the different structures. For the La2MoO6:Eu3+ case, the spectrum is compatible with a C2 point site symmetry. It appears that the energy level scheme is connected with the rare earth oxychloride one, so it is possible to determine accurately sets of crystal field parameters simulating the spectrum. For the other compounds, the Eu3+ ions occupy three different point sites. By using the site-selective excitation on the 5D0 level it is possible to identify the energy level scheme characterizing each point site.

Simulation of the energy level scheme of Nd3+ and Eu3+ ions in rare-earth orthovanadates and phosphates

The absorption spectra of the Nd3+ ion in the tetragonal xenotime-type NdVO4 and in the monoclinic monazite-type LaVO4, LaPO4 and NdPO4 as well as the luminescence of the Eu3+ ion in LaVO4 and LaPO4 were measured and the spectra were analysed according to the appropriate symmetry of the RE site. In addition to pure zero-phonon electronic lines the absorption spectra of the Nd3+ ion showed extensive vibronic side bands which were identified with the aid of the measured Raman scattering spectra of LaVO4:Nd3+ and NdVO4. Based on the energy level schemes derived from the absorption and luminescence spectra the parametrization of the free-ion and crystal-field effects were carried out with good results as indicated by the low RMS deviation values. The parameter sets for Nd3+ and Eu3+ ions in the same matrices are consistent with each other but no correlation was found between sets for matrices of different structures.