Spectral diffusion from stimulated spin echoes of phosphorescentF22+centers in MgO

Nonstationary spectral diffusion is observed for $F_2^{}{}_{}{}^{2+}$ centers, in MgO, in the photoexcited ${}_{}{}^3{}_{}{}^{}B_{1u}^{}{}_{}{}^{}$ state by means of optically detected stimulated-echo-decay experiments. It is discussed that two different spectral diffusion processes can be probed for the photoexcited $F_2^{}{}_{}{}^{2+}$-center triplet spins. In addition to the recently reported diffusion due to time-dependent AB-spin interactions, we report here a slower spectral diffusion process that is attributed to a migration of optical ${}_{}{}^3{}_{}{}^{}B_{1u}^{}{}_{}{}^{}-{}_{}{}^1{}_{}{}^{}A_g^{}{}_{}{}^{}$ transition energy or electron tunneling processes in the MgO host.