Application of Thermoluminescence and Reflectance Methods to Study of Lattice Defects in Alumina Ceramics

Alumina ceramics irradiated with gamma rays emit light of varying intensity as they are warmed. The resulting glow curve may be resolved into discrete peaks, each of which corresponds to a separate electron trapping level. The energy depth of each trap may be estimated from the glow-peak temperature and the temperature at which the light intensity reaches half its maximum value. Resolved glow curves are presented for a series of alumina ceramics including specimens having less than 100 p.p.m. of impurities as well as others contaminated with low concentrations of Si, Ti, Fe, Mg, and Ca oxides. Curves are also given for high-purity aluminas which were heated in oxygen and in hydrogen after firing. Where possible, glow peaks are identified with the causative impurity ion or annealing treatment, and estimated trap depths are tabulated. Because of its inverse relation to optical absorption, reflectance is also sensitive to changes in the number and type of lattice defects. Annealing in oxygen and introduction of Ca²⁺ ions produce a significant lowering of the reflectance of irradiated alumina ceramics, whereas exposure to hydrogen has the opposite effect.