Jahn-Teller effect in the 4T2g state

Jahn-Teller Effect in Laser Crystal LiCaAIF6 Cr3+ 

We have followed a phenomenological approach and used the cluster model [18]. In this model the eg-type distortion interacts more strongly with the electronic state of an octahedral coordinated Cr3+ ion than the distortions of t2g symmetry. According to Ham [19], we assume that the continuum of vibrational modes with eg character can be approximated by a single mode with an effective frequency o , mass /r and coupling constant V. The collective coordinates of the eg mode are conventionally known as Qe x2 — y2) and Qs ( 3z2 — r2). The linear Jahn-Teller Hamiltonian in equation (1) for the X state is [18]  

Here Pa(a = 6, e) is the momentum conjugate to Qa. In the absence of spin-orbit interaction, the e vibration does not mix the orbital components of the 4T2 g and we have vibrational potential energy surfaces consisting of three separate ( disjoint ) paraboloids in the two-dimensional (2D) space of the Qe and Qe coordinates of the e vibration. The Jahn-Teller coupling leads only to a uniform shift (—ZsPJX = — V2/2fia 2 = —Sha ) of all vibronic levels. 

We have calculated the energy of low-lying levels of Cr3+ doped in LiCaAlF6 crystal taking into account the vibrations of the complex CrFg-. The fine structure of X of Cr3+ ion has been obtained by diagonalization of the Eisenstein matrices and 

The authors wish to thank CNCSIS (Romania) for financial support of this chapter, under Grant No. 12625/1998. 

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