Oliver S. Wenger and Hans U. Güdel
Optical spectroscopy of CrCl₆^3- doped Cs₂NaScCl₆: Broadband near-infrared luminescence and Jahn-Teller effect
J. Chem. Phys. 114, 5832-5841 (2001)                 

Abstract: Single crystals of 4.1% Cr³⁺ doped Cs₂NaScCl₆ were studied by variable temperature optical absorption and luminescence spectroscopy. The ⁴A_2g ⁴T_2g transition exhibits a great deal of fine structure both in absorption and emission spectra. The dynamic Te Jahn-Teller effect in the Cr^{3+ 4}T_2g excited state is analyzed on the basis of the Ham quenching in the ⁴T_2g spinor splitting and the vibrational fine structure in the 7 K ⁴T_2g ⁴A_2g luminescence spectrum. The combined effect of the a_1g and e_g distortions leads to a net axial compression of the CrCl₆^3- equilibrium geometry by 0.029 Å, and an equatorial expansion by 0.088 Å in the ⁴T_2g excited state relative to the ⁴A_2g ground state. These results are compared to those from other Cr³⁺ doped chloride and bromide elpasolites, and their different room temperature luminescence uantum yields are discussed on the basis of their different ⁴T_2g excited state distortions. Temperature dependent luminescence and lifetime measurements show that in Cr³⁺:Cs₂NaScCl₆ at room temperature the luminescence quantum yield is about 0.7.