Excitation-power dependent photoluminescence (PL) studies on CdSe quantum dot thin films under ambient conditions reveal complementary processes that alter the ensemble spectral characteristics. Auger charging and photo-oxidation result in PL quenching, while reversible gas adsorption activates PL by pushing the surface-trapped carrier back into the dot core. Under high excitation power, the PL is enhanced by photochemical formation of an inorganic oxide layer. A correlation between ensemble PL behavior and embedded intensity fluctuations supports this model. (C) 2004 Elsevier B.V. All rights reserved.