Optical pumping cycle of exchange-coupled F+-centre pairs in MgO and CaO

Abstract

In n-irradiated CaO and MgO crystals, triplet-state defects are produced in which two electrons are trapped in the O2- sites of a linear trivacancy configuration O2--Ca2+-O2- parallel to the (100) crystal direction. The electronic spins are coupled antiferromagnetically to give a ground-state singlet 1A1g for these F+-centre pairs, the first excited level 3A2u being thermally populated at room temperature. Measurements of the 3A2u state EPR spectrum at 1.4K under optical excitation demonstrates that optical spin alignment memory is induced during the optical pumping cycle.