Angular dependence of recombination luminescence-detected EPR in a ZnO crystal

Angular dependency of electron paramagnetic resonance, optically detected by UV-excited recombination luminescence (RL-EPR), was measured for nominally pure ZnO single crystals. Observed magnetic resonances belong to the broad yellow RL band with slow decay centred at 610 nm, which is characteristic of untreated ZnO crystals. In the sample, irradiated with the 266 nm UV laser, an additional RL band centred at 740 nm appears, which has considerably faster decay time than the yellow one. This RL band is characteristic of the luminescence of Fe³⁺ ions in the ZnO crystals. It could be observed only after the UV laser treatment. No RL-EPR signal was detected for this RL band. Our spectral simulations show that the observed angular dependences of the RL-EPR spectra can be described considering a simultaneous contribution from two types of deep acceptor centres, i.e. Li_Zn and a zinc vacancy, V_Zn. (paper)