Defect Luminescence of Thin Films of Cu20 on Copper

Films of Cu20, 30 ~m thick, have been grown on copper metal foil at 1000 ~ in 1 % O2/Ar, heat-treated without O2 present at a number of lower temperatures, and quenched in water. The room temperature emission at 980 nm and its excitation spectrum, attributed to relaxed excitons at copper vacancies, are similar to reported photoluminescence from thick crys-tals. Apparent quenching of luminescence by interaction among vacancies i observed for sufficiently high copper vacancy concentration. Heat-treatment does not produce copper vacancies, but redistribution of vacancies can increase their photoluminescence by nearly two orders of magnitude. Under the present copper oxidation conditions, the enhanced con-centration of copper vacancies near the Cu20 surface suggests that the rate of oxidation is limited by the diffusion of these vacancies. The properties of Cu20 have been studied for decades. This research has been largely confined to bulk crys-tall ine samples. Another approach to the study of the properties of materials is to examine thin films. Such an approach raises the possibility that film properties may be found which are significantly different fro