Abstract
Films of 
, 30 μm thick, have been grown on copper metal foil at 1000°C in 
, heat‐treated without 
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 crystals. Apparent quenching of luminescence by interaction among vacancies is 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 concentration of copper vacancies near the 
surface suggests that the rate of oxidation is limited by the diffusion of these vacancies.