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Excess Zn in ZnO was experimentally investigated. The ZnO samples tested were prepared by heat treatment of ZnO powder or polycrystalline ceramics at a temperature of 900 °C and at fixed Zn pressures from 0.2 to 0.6 of saturated Zn vapour pressure at a given temperature. To determine the excess Zn, atomic absorption photometry of Zn vapour was used under conditions of solid-vapour equilibrium. The optical absorbance, proportional to the concentration of Zn atoms in the vapour phase, was registered photoelectrically on the Zn resonance line. During the atomic absorption photometry measurements all excess Zn was extracted from the solid state into the vapour phase. The analysis of the temperature dependence of Zn pressure indicated that the value of Zn excess lies in the concentration interval of 10 18 -10 19 cmand depends on the sample history and the conditions of preliminary heat treatment. The experimental results were used for preliminary estimation of high-temperature defect equilibrium in ZnO. Chemical analysis is not a reliable technique for evaluating the excess Zn in ZnO. Chemical analysis can only serve as a qualitative technique for comparing different samples. In our investigations of atomic absorption photometry of polycrystalline II-VI materials it became evident that the metal component adsorbed on crystallite surfaces must be taken into account [5]. In Ref.[6] different HTDE models from different authors are compared. ZnO exhibits n-type high-level electrical conductivity, which is due to intrinsic donor [7] or to hydrogen as a shallow donor [8]. The dominating high-temperature defects are interstitial Zn [9][10][11] or oxygen vacancies [2,12]. Atomic absorption photometry studies of the nonstoichiometry of II-VI compounds have shown that the analytically determined concentration of the metal component excess appears to be bigger than the concentration of electrically active defects [13,

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Transparent zinc oxide ceramics, undoped and doped with 0.1-2.0 wt% Er3+ ions were fabricated by uniaxial hot pressing of commercial oxide powders. The ceramics were characterized by X-ray diffraction, SEM, EDX, Raman, X-ray and optical spectroscopy. The analysis of morphology of Er3+:ZnO ceramics reveals that the main components of texture are hexagonal prism planes similar to those for undoped ceramic. The ZnO grain size decreases with addition of Er2O3. The Er3+ ions are distributed between the ZnO grains and the Er2O3 crystals and do not enter the zinc oxide structure. The luminescence spectra of Er3+:ZnO ceramics contain emission bands originating from the intra-4f shell transitions of Er3+ ions and bands assigned to defect states at ZnO. The X-ray luminescence spectra indicate the possible energy-transfer between the ZnO grains and Er3+ ions. The defect luminescence band becomes weaker and the X-ray luminescence decay time decreases as the erbium concentration is increased.

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