Uniaxial stress effect and spin-lattice coupling in the 3 T1u relaxed excited states of F centres in CaO

Abstract

The effect of uniaxial stress on the EPR spectrum of the 3T 1u relaxed excited states of F centres in CaO is reported. From symmetry considerations only, an effective Hamiltonian is derived in order to describe the spin-lattice coupling in a 3T1u level undergoing a strong coupling to Eg modes of vibration (static Jahn-Teller effect). It is shown that the spin-lattice coupling is about four orders of magnitude smaller than the orbit-lattice coupling. The physical origin of the spin-lattice coupling is analyzed ; three mechanisms are considered : variation with the applied strain of (i) the spin-orbit interaction, (ii) the dipole-dipole interaction, (iii) the Jahn-Teller stabilization energy, this last mechanism being the most effective. Estimates for the parameters of the vibrational coupling to Eg modes, of the spin-orbit interaction, and of the dipole-dipole interaction are given.