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1

The Emission Spectra for the Cs_2NaScCl_6:MoCl_6^{3-} System in the Fm3m Space Group

100%

Acevedo R., Meruane T., Navarro G.

Acta Physica Polonica A

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2001

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vol. 99

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issue 2

233-242

EN

On the basis of the data reported by Flint and Paulusz, we have undertaken a theoretical investigation of the intensity mechanism for the various emissions:Γ_8(^2T_{2g} ) → Γ_8(^4A_{2g}), Γ_8(^2E_{g}), Γ_8(^2T_{1g}), Γ_6(^2T_{1g}) for the Cs_2NaScCl_6:MoCl_6^{3-} system in the Fm3m-space group. The experimental data available refer to the visible and near infrared luminescence spectra of MoCl_6^{3-} complex ion in different hosts, such as Cs_2NaMCl_6 (M = Sc, Y, In), measured between 15,000 cm^{-1} and 3,000 cm^{-1} at liquid helium temperatures. At least, five luminescence transitions have been identified and assigned and each of them show extensive vibronic structure. A careful analysis of this experimental data shows that for the various observed electronic transitions, the vibrational frequencies change only slightly, and therefore there is no indication that the system undergoes both a significant and relevant Jahn-Teller distortion (along an active coordinate). There is however clear evidence that for the chloro-elpasolites, there is a strong resonance interaction between ν_3(τ_{1u} : stretching) of the MoX_6^{3-}, complex ion and that of the host when M = In, Y. Thus for M = Sc, the slighter higher host ν_3, wave number is likely to minimize the effect of this coupling. This evidence will allow us for the Cs_2NaScCl_6:MoCl_6^{3-} system to neglect, in the first-order approximation, the coupling among the internal and the external vibrations and to proceed using a both a molecular and the independent system models.

2

Ligand-Framework Coupling Vibrations. The ^2E_g → ^4A_{2g} Transition in the Cr(CN)_6^{3-} Complex Ion

100%

Acevedo R., Passman M., Navarro G.

Acta Physica Polonica A

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2001

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vol. 99

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issue 2

215-232

EN

In this research paper we examine the role played by the bending vibrational modes of motion, δ(Cr-C-N) to influence the observed overall and relative vibronic intensity distribution for the ^2E_g → ^4A_{2g} phosphorescence of the Cr(CN)_6^{3-} complex ion. The calculation was carried out assuming both: (a) a seven-atom system model (molecular approximation) and (b) a negligible distortion from the octahedral symmetry for the system. The ligand polarization formalism was employed with reference to this system, since the ligand subsystems (CN)^{-1} are highly polarizable and as a consequence a conventional crystal field calculation would be both unrealistic and unappropriate. This system was chosen since there is a solid evidence to conclude that vibrations of the same type in the τ_{1u} and τ_{2u} symmetry blocks induce comparable intensity. This is a clear indication that both the τ_{1u} and τ_{2u}: δ(Cr-C-N) bending vibrations are exceptionally efficient to promote this radiative transition. This dynamical model is tested against the experimental data and it is shown that the model calculation, though approximate, gives results in excellent agreement with experiment.

3

Absorptions and Emissions for the TmCl_6^{3-} Ion in Cs_2NaTmCl_6

100%

Acevedo R., Hurtado O., Portillo C., Stręk W.

Acta Physica Polonica A

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2001

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vol. 100

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issue 6

829-844

EN

In this work we report both experimental and theoretical studies regarding the Cs_2NaTmCl_6 elpasolite-type system, for which we have an updated database from linear and nonlinear optics. Both the absorption and the emission spectra for this system are rather complicated and a generalized vibronic crystal field-closure-ligand polarization calculation model has been employed to rationalize the observed spectral intensities. The calculation has been carried out by neglecting the interaction among the internal and the external vibrations and theoretical calculations have been performed with reference to both the emissions ^3H_4(Γ_i)>^3F_4(Γ_j) and the absorptions ^3H_6(A_1)> ^3F_4(Γ_i), ^1G_4(Γ_i), ^3H_5(Γ_l) withΓ_k (k=i,j)=A_1,E,T_1,T_2 andΓ_l=E, ^aT_1, ^bT_1,T_2. The advantages and disadvantages of our model calculation are discussed in the text, and despite the simplicity of the model it is shown that it has got some utility and flexibility to gain understanding in these complex phenomena.

4

Spectral Intensities for the Emission |^4S_{3/2}Γ_8〉 → |^4I_{15/2}Γ〉in the Cs_2NaErCl_6

88%

Acevedo R., Soto-Bubert A., Navarro G., Meruane T., Stręk W.

Acta Physica Polonica A

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2004

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vol. 105

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issue 3

233-251

EN

We report explicit vibronic intensity calculations for the |^4S_{3/2}Γ_8> → |^4I_{15/2}Γ>excitations in the Cs_2NaErCl_6 elpasolite-type systems, based upon new and updated experimental data, obtained from optical absorption measurements made at 10 K, in the energy range from 6,000 up to 26,000 cm^{-1}. Our calculation model is a generalization of the vibronic crystal field-ligand polarization method and the calculation is performed using a minimum set of adjustable parameters - all and each of them have a clear physical meaning. Our strategy was chosen so as to make a significant distinction with previous calculations, performed by other authors, who have worked out a model originated from a supra-parameterized scheme, within the framework of the superposition model of Newman. Throughout the course of the current work, it is shown that our model is suitable to handle this kind of calculations and also that the numerical results obtained are in fairly good agreement with experiment.

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4 Acta Physica Polonica A

1 2004

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2 Meruane T.

2 Stręk W.

1 Hurtado O.

1 Passman M.

1 Portillo C.

1 Soto-Bubert A.

The Emission Spectra for the Cs_2NaScCl_6:MoCl_6^{3-} System in the Fm3m Space Group

Ligand-Framework Coupling Vibrations. The ^2E_g → ^4A_{2g} Transition in the Cr(CN)_6^{3-} Complex Ion

Absorptions and Emissions for the TmCl_6^{3-} Ion in Cs_2NaTmCl_6

Spectral Intensities for the Emission |^4S_{3/2}Γ_8〉 → |^4I_{15/2}Γ〉in the Cs_2NaErCl_6