Manifestation of spin-dependent recombination in afterglow of zinc oxide crystals

Long-lasting afterglow of ZnO single crystals grown by hydrothermal method has been studied using high-frequency (94 GHz) optically detected magnetic resonance (ODMR) at helium temperatures. Giant (up to 30%) afterglow intensity-detected electron paramagnetic resonance signals of shallow donors and deep acceptors, which are lithium atoms substituting for zinc in the ZnO lattice, unambiguously indicate a spin-dependent character of the donor-acceptor recombination. The observed variations in the shape of the afterglow-detected ODMR spectra of lithium acceptors with time passed after irradiation are associated with the difference in the recombination rates of shallow donors with axial and non-axial LiZn centers and with a change in the recombination character with time.