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ZnO bulk single crystals were doped with sodium by thermal diffusion. Positron annihilations spectroscopy confirms the filling of zinc vacancies, to >6 μm deep in the bulk. Secondary-ion mass spectrometry measurement shows the diffusion of sodium up to 8 μm with concentration (1–3.5) × 1017 cm−3. Broad photoluminescence excitation peak at 3.1 eV, with onset appearance at 3.15 eV in Na:ZnO, is attributed to an electronic transition from a NaZn level at ∼(220–270) meV to the conduction band. Resistivity in Na doped ZnO crystals increases up to (4–5) orders of magnitude at room temperature.

Reactively sputtered Ni x Co (3−x) O 4 films (x = 1.5, 1.0, and 0.75) were grown and subsequently irradiated with 5.5 MeV Si + ions to investigate effects of lattice-site and charge state distribution. Films were characterized before and after irradiation by X-ray diffraction, X-ray photoemission spectroscopy, Rutherford backscattering spectroscopy, electric resistivity measurements, and temperature-dependent AC and DC magnetometry. Results indicate that ion irradiation induces oxygen loss, partial reduction of nickel, and an increase in both low-temperature ferrimagnetism and room-temperature conductivity. Frequency-dependent AC magnetic susceptibility measurements indicate a spin-glass-like transition at low temperature which moves to higher temperature after irradiation. Significance of the charge transfer for magnetism and conduction in a mixed spinel with Co 2+ , Co 3+ , Ni 2+ , and Ni 3+ in tetrahedral and octahedral sites is discussed.

The effect of hydrogen on ZnO while annealing at 1370 K under oxygen-poor conditions with excess Zn vapor or Ti metal is studied. ZnO turns red only when hydrogen is present in a complex with oxygen vacancies. A practical method is described to remove hydrogen from ZnO in a sealed ampoule and to bind it to Ti metal. Hydrogen coupled to an oxygen vacancy is the simplest defect to explain the observations. The coloration is reversible at 1370 K by adding or removing hydrogen, consistent with an activation energy >1.5 eV. In red ZnO Hall data show a shallow donor level around 45 meV.

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