Fast Neutron-Induced Enhancement of the I8 Exciton Emission in ZnO Bulk Single Crystals

Zinc oxide (ZnO) is a wide-bandgap semiconductor with important optoelectronic, photonic, and radiation-related applications. In this work, hydrothermally grown ZnO bulk single crystals were irradiated with fast neutrons and characterized using low-temperature photoluminescence (PL) spectroscopy to investigate irradiation-induced changes in the Ga-related donor-bound exciton (I₈). The Zn-polar surfaces were exposed to fast neutrons for irradiation durations of 2 and 5 min. The PL measurements showed a reproducible enhancement of the Ga-related I₈ emission intensity, with increases of approximately 33% after 2 min and 82% after 5 min relative to the unirradiated reference crystal. The selective enhancement of the I₈ emission is consistent with increased Ga-related donor activity associated with the proposed Zn-to-Ga neutron transmutation mechanism, although irradiation-induced defect formation and redistribution may also contribute to the observed optical response. Under the irradiation conditions investigated, fast-neutron exposure produced substantial enhancement of the I₈ emission within only a few minutes. However, direct quantitative comparison with previously reported slow-neutron irradiation should be interpreted with caution because the two studies employed different neutron energies, fluences, and irradiation conditions. These findings demonstrate the potential of fast-neutron irradiation for modifying the low-temperature optical response of hydrothermally grown ZnO and provide a foundation for future investigations of neutron-induced defect and donor engineering in wide-bandgap oxide semiconductors.