201 Electronic spectra and crystal field analysis of Yb2+ in SrCl2 (original) (raw)
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Electronic spectra of Yb[sup 2+]-doped SrCl[sub 2]
The Journal of Chemical Physics, 2010
The absorption and emission spectra of Yb 2+ -doped SrCl 2 have been calculated on the basis of ab initio quantum chemical calculations which consider recently found, unexpected excited states with double-well energy curves and complex electronic structure, resulting from avoided crossings between Yb-trapped excitons and Yb impurity states, which influence prominent spectral features.
201 Phys rev B 77 2008 085114 SrCl2 Yb
The 10 K emission spectrum and absorption spectrum between 27 000 and 30 000 cm −1 have been recorded and assigned for SrCl 2 :Yb 2+ ͑0.05 and 1 at. %͒, where the divalent ion is situated at a site of O h symmetry with eightfold coordination to chloride ions. In emission, two broad bands are observed at room temperature and these are assigned to orbitally forbidden and allowed transitions from 4f 13 5d to the 4f 14 ground state 1 S 0 . Nearly all of the transitions, except for some of the highest energy absorption bands, are spin forbidden in the sense that the transition final states are dominated by spin triplet components, while the initial state is a pure spin singlet. The spectral intensities in the absorption spectrum have been fitted satisfactorily, following the crystal field calculation for 4f 13 5d in which four parameters were freely varied. There is no need to cite the presence of Yb 2+ ions at several sites in order to explain the observed absorption bands, as has been done previously, but we invoke the coparticipation of the ͑low-lying͒ 4f 13 6s configuration. The rationale for the parameter values is explained in detail as are the effects of parameter variations. The calculated radiative lifetime for the orbitally allowed emission transition is in agreement with that measured at low temperature ͑ϳ1 s͒ and the nonradiative rate from the luminescent level has been modeled as a function of temperature.
Yb[sup 2+]-doped SrCl[sub 2]: Electronic structure of impurity states and impurity-trapped excitons
The Journal of Chemical Physics, 2010
First principles electronic structure calculations of the excited states of Yb 2+ -doped SrCl 2 crystals up to 65000 cm −1 reveal the existence of unexpected excited states with double-well potential energy surfaces and dual electronic structure lying above and very close in energy to the 4f 13 5d manifold, with which they interact strongly through spin-orbit coupling. The double-well energy curves result from avoided crossings between Yb-trapped exciton states (more stable at short Yb-Cl distances) and 4f 13 6s impurity states (more stable at long Yb-Cl distances); the former are found to be pre-ionization states in which the impurity holds the excited electron in close lying empty interstitials located outside the YbCl 8 moiety. Spin-orbit coupling between the double-well states and lower lying 4f 13 5d impurity states spreads the dual electronic structure character to lower energies and, hence, the instability of the divalent oxidation state is also spread. To some extent, the dual electronic structure (impurity-trapped exciton -impurity state) of some excited states expresses and gives support to hypotheses of interaction between Yb 2+ and Yb 3+ pairs proposed to understand the complex spectroscopy of the material and conciliates these hypotheses with interpretations in terms of the existence of only one type of Yb 2+ defect. The results presented confirm the presence of impurity states of the 4f 13 6s configuration among the 4f 13 5d manifolds, as proposed in the literature, but their energies are very different from those assumed.
Absorption, excitation and emission spectra of SrCl2:Eu2+
Chemical Physics Letters, 2006
The 10 K ultraviolet emission spectrum and low-energy ultraviolet absorption spectra are reported for dilute SrCl 2 :Eu 2+ . Only one luminescent state is observed under various synchrotron radiation excitation wavelengths. The broad room temperature 4f 6 5d ! 4f 7 emission spectrum, peaking at 410 nm, sharpens considerably at 10 K and vibrational progressions in the totally symmetric Sr-Cl stretching mode of 210 cm À1 upon the zero phonon line and vibronic structure are predominant. The low-energy 4f 7 ! 4f 6 5d absorption spectrum comprises similar vibronic structure but many transitions overlap. The emission, absorption and excitation spectra are well simulated by calculation.
Journal of Luminescence, 2001
Crystals of 2% Tm 2þ doped SrCl 2 were studied by variable temperature optical absorption and luminescence spectroscopy. The absorption spectrum consists of the weak 4f 13 intraconfigurational 2 F 7=2-2 F 5=2 transition around 8840 cm À1 and a series of intense parity allowed f-d transitions above 15; 000 cm À1 : Luminescence is observed from the 4f 13 2 F 5=2 excited state as well as from the lowest-energetic 4f 12 5d excited state at all temperatures between 10 and 300 K: Upconversion luminescence from the latter is observed after cw-(lamp) excitation at 8840 cm À1 into 2 F 5=2 at 15 K; as well as after pulsed (laser)
Effective Hamiltonian parameters forab initioenergy-level calculations of SrCl2:Yb2+and CsCaBr3:Yb2+
Journal of Physics: Condensed Matter, 2013
Calculated energy levels from recent ab initio studies of the electronic structure of SrCl 2 :Yb 2+ and CsCaBr 3 :Yb 2+ are fitted with a semi-empirical "crystal-field" Hamiltonian, which acts within the model space 4f 14 +4f 13 5d+4f 13 6s. Parameters are obtained for the minima of the potential-energy curves for each energy level and also for a range of anion-cation separations. The parameters are compared with published parameters fitted to experimental data and to atomic calculations. The states with significant 4f 13 6s character give a good approximation to the impurity-trapped exciton states that appear in the ab initio calculations.
Simulation of 4f–5d transitions of Yb 2+ in potassium and sodium halides
Journal of Physics: Condensed Matter, 2008
The free ion energy level parameters of Yb 2+ are obtained by fitting the 4f 13 5d Yb 2+ free ion energy levels. A model is proposed for scaling these parameters so that they are appropriate for Yb 2+ in crystals. Treating the scaling factor, the barycenter energy E exc of the 4f 13 5d configuration, and the crystal-field splitting parameter B 4 (dd) as free parameters and adopting the 4f crystal-field parameters of the 4f 13 configuration Yb 3+ ion in other hosts with the same ligands, the absorption spectra of Yb 2+ in MX (M = K, Na; X = F, Cl, Br, I) hosts are well simulated. A model is proposed for taking the effect of charge compensation into account and this shows that the inclusion of charge compensation effects does not significantly alter the calculated electronic absorption spectra but may considerably change the dynamics of the system.
Vibronic intensities in the absorption spectra of Yb3+
Physical Review B, 1996
The oscillator strengths and relative vibronic intensity distribution of the ( 2 F 5/2 )⌫ 8 ,⌫ 7 ←⌫ 6 ( 2 F 7/2 ) transitions of the YbCl 6 3Ϫ complex ion at an octahedral symmetry site in the Cs 2 NaYbCl 6 lattice have been measured experimentally and calculated using a combined vibronic crystal-field-ligand polarization approach. The vibronic crystal-field contribution to the total transition dipole moment of the various excitations was worked out both with and without invoking closure over the central metal ion intermediate electronic states and the intensity was assumed to be derived from both a parity and a spin-allowed d← f transition with the cooperation of the odd-parity vibrational modes of the complex ion. Quadrupole and hexadecapole terms have been included in the ligand polarization contribution. Attention has been given to the correct choice of phases for both the electronic and the vibrational wave functions in order to ensure the right sign for the cross term which couples together the crystal field and the ligand polarization transition dipole vectors. The ab initio formalism employed avoids the use of any adjustable parameters in calculating the vibronic intensities. The calculated oscillator strengths of vibronic transitions are within order of magnitude agreement with experimental values. The sensitivity of the calculated values to the use of different force fields has been investigated. The experimentally measured total oscillator strengths for the ( 2 F 5/2 )⌫ 8 ,⌫ 7 ←⌫ 6 ( 2 F 7/2 ) transitions of YbCl 6 3Ϫ diluted into the transparent Cs 2 NaGdCl 6 host remain constant with change in Yb 3ϩ concentration although deviation of the chromophore from octahedral symmetry is evident at intermediate concentrations. A comparison with the vibronic sidebands of Cs 2 LiYbCl 6 and Cs 2 KYbF 6 is made. ͓S0163-1829͑96͒05329-5͔
EPR and optical spectroscopy of Yb 3+ ions in CaF 2 and SrF 2
Journal of Luminescence, 2003
The Yb 3+ paramagnetic center of the trigonal symmetry (''oxygen'' paramagnetic center T 2 ) in CaF 2 and SrF 2 single crystals is studied by EPR and optical spectroscopy. The Stark level energies of the Yb 3+ multiplets are established from absorption, luminescence and excitation luminescence spectra and the crystal field parameters are calculated. r