Phase relaxation of photoexcited triplet spins in CaO

Abstract

Spin dephasing in the photoexcited $^{3}B_{1}$ state of the ${F}_{2}^{2+}$ center in CaO is investigated using techniques for optical detection of microwave-induced coherent transients. Measurements of the spin-echo decay were performed at different (low) temperatures and (low) magnetic field strengths. The spectral diffusion results give quantitative support for a model in which the dephasing is due to random modulation of the dipolar coupling between the excited $S=1$ spins and ${F}^{+}$-center spins of $S=\frac{1}{2}$. A projection operator formalism is used to treat the dipolar-induced dephasing. The theory also allows for the experimental determination of the ${F}^{+}$-center spin-dephasing rate. It appears that between 1 and 10 K the phenomenon of one-phonon assisted exchange narrowing occurs in the ${F}^{+}$-center spin ensemble.