Phonon-assisted conversion between the Jahn-Teller states of the phosphorescentFcenter in CaO: Optically detected magnetic resonance under uniaxial stress

From optically detected magnetic resonance spectra and time-resolved measurements of the phosphorescent $F$ center in a nondegenerate state ([101] stress) and in a doubly degenerate Jahn-Teller state ([100] stress), the static coupling of the photoexcited spin vibronic system to external stress as well as the nature of the dynamics (at 1.5 K) involved in the transitions between the spin-vibronic levels have been studied. To describe the static coupling between the $T_{1u}\otimes e_g$ ($S=1\mathrm{}$) spin vibronic system and strain a spin Hamiltonian was derived. Apart from spin-lattice relaxation within a single vibronic Jahn-Teller state, also another relaxation channel was shown to be operative which consists of a phonon-assisted conversion between different vibronic Jahn-Teller states with conservation of spin-state character.