Magnetic dipole and vibronically induced electric dipole intensities of the 5 D 4 → 7 F J transitions of Tb 3+ in Cs 2 NaTbCl 6

Author： Faulkner Thomas Richardson F.S.

Publisher： Taylor & Francis Ltd

ISSN： 1362-3028

Source： Molecular Physics, Vol.36, Iss.1, 1978-07, pp. : 193-914

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Abstract

An analysis of the emission intensities associated with the 5 D 4 → 7 F J ( J =2, 3, 4, 5, and 6) transitions of Tb 3+ in crystalline Cs 2 NaTbCl 6 is performed. The energy levels and crystal-field states associated with the octahedral ( O h ) TbCl 6 3- clusters are calculated using a weak-field crystal-field model. Magnetic-dipole strengths are calculated for all transitions occurring between the crystal-field components of 5 D 4 and the crystal-field components of 7 F 2 , 7 F 3 , 7 F 4 , 7 F 5 , and 7 F 6 . Vibronically induced electric-dipole strengths are also calculated for the transitions between the 5 D 4 → 7 F J ( J =2, 3, 4, 5, and 6) crystal-field components. In the vibronic intensity model, both ‘static' and ‘dynamic' coupling between the electronic charge distributions on the metal ion (Tb 3+ ) and ligands (Cl - ) are included. Only the ungerade vibrational modes localized within the TbCl 6 3- cluster are considered as intensity-promoting modes. Assuming a thermally equilibrated 5 D 4 emitting level and lorentzian band shapes, emission spectra are calculated for the 5 D 4 → 7 F 2 , 7 F 3 , 7 F 4 , 7 F 5 , and 7 F 6 transitions of the Tb 3+ ion. These calculated spectra are compared with the experimentally determined emission spectra for Cs 2 NaTbCl 6 (at T =77 K). The observed dominance of magnetic-dipole intensity in the transitions of Δ J = ±1 free-ion parentage is well accounted for by our intensity calculations. The observed near-equivalence of the magnetic-dipole and vibronically induced electric-dipole contributions to the intensities of the transitions of Δ J =0, ±2 free-ion parentage is also reproduced by our intensity calculations. In general, the intensity model leads to excellent agreement between the calculated and experimental emission spectra in all regions except that associated with the 3 D 4 → 7 F 4 transition.