ZnO nano-powders were synthesised by mixing equal volumes of 0.05 M zinc chloride in ethanol and 0.20 M sodium hydroxide (either 97+% or semiconductor grade) in ethanol, for six hours at room temperature. The resulting cloudy solutions were centrifuged and the resulting powders rinsed before being dried under vacuum. The synthesised ZnO powders are referred to as: HP ZnO; made with the semiconductor grade NaOH, and ZnO; made with the 97+% NaOH.

Cathodoluminescence (CL) spectra and images were collected at 5 K of these as-prepared specimens, as well as specimens annealed at 700°C for 10 minutes in an atmosphere of 5% H₂ / 95% Ar. The HP ZnO displayed a much more intense UV near band edge (NBE) emission compared with ZnO, and lacked the broad green defect related emission observed in the specimen prepared with 97+% NaOH. Annealing in H₂ increased the intensity of the NBE emission in both powders although the HP ZnO NBE emission remained by far the most intense, while the intensity of the green defect emission of the ZnO was greatly reduced.

The NBE emission from H₂ annealed HP ZnO contained recombination centres at 3.36 eV; attributed to I_6/6a Aluminium donor and 3.32 eV; an unidentified acceptor-bound exciton emission with LO phonon replicas at 3.25 eV and 3.18 eV. The H₂ annealed ZnO displayed weaker intensity emissions at the same energies in addition to a weak green defect emission at 2.40 eV.

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