4f(n)-> 4f(n)-15d transitions of the heavy lanthanides: Experiment and theory (original) (raw)
Related papers
Spectroscopy and Calculations for 4f N → 4f N –1 5d Transitions of Lanthanide Ions in K 3 YF 6
The Journal of Physical Chemistry A, 2012
In the present work, we report on the combined experimental and theoretical studies of the 4f−5d spectra of Ce 3+ , Pr 3+ , Nd 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , and Er 3+ ions in a newly synthesized K 3 YF 6 matrix. The low temperature experimental 4f−5d excitation spectra have been analyzed and compared with the results of the energy-level and intensity calculations. For this theoretical analysis, the extended phenomenological crystal-field model for the 4f N−1 5d configuration (i.e., the extended f-shell programs, developed by Prof. M. F. Reid) and exchange charge model (developed by Prof. B. Z. Malkin) have been used together to estimate the crystal field parameters and implement the spectral simulations. On the basis of the results of the performed theoretical analysis, we suggest the most probable positions occupied by optically active ions. Although the spectra of only eight lanthanide ions have been studied, the Hamiltonian parameters of the 4f N−1 5d configuration have been evaluated for the whole lanthanide series and reported here for the first time, to give a complete and unified description of the spectroscopic properties of the trivalent rare earth ions in the chosen host. In addition to the studies of the 4f−5d transitions, various possible competitive excitation channels overlapping with 4f−5d ones have also been discussed, where a theoretical scheme giving rudiments to understand 4f−6s spectra are proposed for the first time. An excellent agreement between the calculated and measured excitation spectra shapes confirms validity of the performed analysis. The obtained parameters of the crystal field Hamiltonians for different ions and various electron configurations can be used in a straightforward way to generate the energy level positions and calculate the particular transition intensities for any rare earth ion in any particular spectral region. With the aid of the obtained parameters, the positions of the lowest energy levels of the 4f N , 4f N−1 5d ,and 4f N−1 6s configurations of rare earth ions and 4f N+1 (np) 5 configuration of rare earth ions and ligands (corresponding to the ligand−impurity ion charge transfer transitions) in the band gap of K 3 YF 6 have all been estimated. The obtained Hamiltonian parameters and energy levels diagrams, which include the electronic structure of a host material, can be used as a starting point for analysis of spectroscopic properties of trivalent lanthanides in similar fluorides.
Electronic structure of fluorides: general trends for ground and excited state properties
The European Physical Journal B, 2011
The electronic structure of fluorite crystals are studied by means of density functional theory within the local density approximation for the exchange correlation energy. The ground-state electronic properties, which have been calculated for the cubic structures CaF 2 ,SrF 2 , BaF 2 , CdF 2 , HgF 2 , β -PbF 2 , using a plane waves expansion of the wave functions, show good comparison with existing experimental data and previous theoretical results. The electronic density of states at the gap region for all the compounds and their energy-band structure have been calculated and compared with the existing data in the literature. General trends for the ground-state parameters, the electronic energy-bands and transition energies for all the fluorides considered are given and discussed in details. Moreover, for the first time results for HgF 2 have been presented.
4fn→4fn-15d transitions of the light lanthanides: Experiment and theory
Physical Review B, 2002
The 4 f n →4 f nϪ1 5d(f d) excitation spectra of the light lanthanides ͑Ce 3ϩ , Pr 3ϩ , Nd 3ϩ , Sm 3ϩ , and Eu 3ϩ ͒ incorporated in LiYF 4 , CaF 2 , and YPO 4 are investigated in the ultraviolet and vacuum-ultraviolet spectral region ͑100-250 nm͒. In these host lattices fine structure ͑zero-phonon lines and vibronic lines͒ is observed for fd transitions involving the lowest 5d crystal-field state. The observation of zero-phonon lines makes it possible to analyze the complicated structure in the fd spectra and to compare the experimentally observed spectra with energy-level calculations for the 4 f nϪ1 5d states. Energy-level and intensity calculations were performed by an extension of the commonly used theory for energy-level calculations of 4 f n states. A good agreement between experiment and theory is obtained for the overall structure using the crystal-field splitting ͑from the spectra of Ce 3ϩ ͒, the parameters for the splitting of the 4 f nϪ1 core ͑from the literature on energy level calculations for 4 f n states͒ and the spin-orbit coupling of the 5d electron and Coulomb interaction between 4 f and 5d electrons ͑from atomic parameters using the computer code of Cowan͒.
4FN↔4FN−15D Transitions of the Trivalent Lanthanides: Experiment and Theory
Journal of Luminescence, 2001
Emission and excitation spectra of 4f n 24f nÀ1 5d transitions of lanthanide ions in LiYF 4 are reported and are succesfully reproduced by energy level calculations using a theoretical model that extends established models for the 4f n configuration to include fd states. Some interesting trends are observed. Lifetime measurements for the spin-allowed fd emission show that the electric dipole matrix element for the fd transition decreases through the lanthanide series. Also the splitting between the high spin and low spin fd states decreases through the lanthanide series. Both effects are reproduced by our model.
AB-INITIO ELECTRONIC STRUCTURE CALCULATIONS OF LANTHANUM FLUORIDE
Lanthanum fluoride (LaF 3 ) is a rare earth metal (REM) fluoride that exists in nature as the tysonite type. Pure LaF 3 crystallize into cubic, tysonite and tetragonal crystal system at different temperatures. However, it's the tysonite (hexagonal) phase is stable at room temperature. Among its key features that make LaF 3 outstanding among other similar RE compounds like La 2 O 3 are being ionic but insoluble in water or organic fluid and have a wide band gap energy about 9.0eV. These characteristics make it a potential applicant in technology revolving around optics, solid state physics and telecommunication. In the study of properties of matter, there are discrepancies between experimental and computational results of electronic and structural properties of LaF 3 . All computation calculations have been done using the Quantum ESPRESSO computer code. DFT have been implemented using ultra soft pseudo potentials and a Generalized Gradient Approximations (GGA). The Brillouin Zone (BZ) is defined by the Monkhorst-pack K mesh with 2×2×1 grid and high symmetry points used are Γ-M-K-Γ-A-L-H-A/L-M/K-H. Third order Birch-Murnghan equation of states (EOS) is used to calculate bands and density of states (DOS) using results obtained from consistent field calculations. After convergence tests, lattice constants attained are a= 7.1661Å,
Physical chemistry chemical physics : PCCP, 2015
Ligand field density functional theory (LFDFT) is a methodology consisting of non-standard handling of DFT calculations and post-computation analysis, emulating the ligand field parameters in a non-empirical way. Recently, the procedure was extended for two-open-shell systems, with relevance for inter-shell transitions in lanthanides, of utmost importance in understanding the optical and magnetic properties of rare-earth materials. Here, we expand the model to the calculation of intensities of f → d transitions, enabling the simulation of spectral profiles. We focus on Eu(2+)-based systems: this lanthanide ion undergoes many dipole-allowed transitions from the initial 4f(7)((8)S7/2) state to the final 4f(6)5d(1) ones, considering the free ion and doped materials. The relativistic calculations showed a good agreement with experimental data for a gaseous Eu(2+) ion, producing reliable Slater-Condon and spin-orbit coupling parameters. The Eu(2+) ion-doped fluorite-type lattices, CaF2:E...
A simple model for the f–d transition of actinide and heavy lanthanide ions in crystals
Current Applied Physics, 2006
The f → d transition model by Duan and co-workers [Phys. Rev. B 66, 155108 (2002); J. Solid State Chem. 171, 299 (2003)] has been very useful in interpreting the f → d absorption, emission and nonradiative relaxation of light lanthanide ions in crystals. However, based on the assumption that the f N −1 core spin-orbit interaction is weak compared to f → d exchange interaction, this model, in the original form, is not applicable to interpretation of the f → d transitions of heavy lanthanide ions or actinide ions in crystals. In this work the model is extended to cover the cases of heavy lanthanides and actinides, where the spin-orbit interaction of f orbitals may be stronger than the f − d exchange interaction.
NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations
Physical Chemistry Chemical Physics, 2011
19 F isotropic chemical shifts for alkali, alkaline earth and rare earth of column 3 basic fluorides are measured and the corresponding isotropic chemical shieldings are calculated using the GIPAW method. When using PBE exchange correlation functional for the treatment of the cationic localized empty orbitals of Ca 2+ , Sc 3+ (3d) and La 3+ (4f), a correction is needed to accurately calculate 19 F chemical shieldings. We show that the correlation between experimental isotropic chemical shifts and calculated isotropic chemical shieldings established for the studied compounds allows to predict 19 F NMR spectra of crystalline compounds with a relatively good accuracy. In addition, we experimentally determine the quadrupolar parameters of 25 Mg in MgF 2 and calculate the electric field gradient of 25 Mg in MgF 2 and 139 La in LaF 3 using both PAW and LAPW methods. The orientation of the EFG components in the crystallographic frame, provided by DFT calculations, is analysed in term of electron densities. It is shown that consideration of the quadrupolar charge deformation is essential for the analysis of slightly distorted environments or highly irregular polyhedra.