The Spin-Mixing Parameters in the Optical Pumping Cycle of the F Centers in KBr and KI

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The spin-mixing parameter ε is the probability that a spin is flipped into the opposite spin level in the optical processes in the presence of a magnetic field. In the Franck-Condon state, the mean and anisotropic parameters ε₀ and δε have been calculated as a function of pumping photon energy E_ph, on a theoretical framework in which the spin-orbit and electron-lattice interactions with Γ₁⁺-, Γ₃⁺-, and Γ₅⁺-modes are included. The effect of the Γ₅⁺-mode is predominant. By using ε₀ and δε calculated, and introducing a mixing parameter ε_r1 in the non-radiative relaxation process, the experimentally-determined E_ph-dependence of the net spin-mixing parameter ε_t and that of δε(1−2ε_r1) have been explained consistently. The ε_ph-dependence of fractional dichroic differential pumping rate has been calculated.