Nonlinear photoluminescence behavior in closely packed CdSe nanocrystal thin films

We report on the cooperative photoluminescence (PL) properties of closely p acked CdSe nanocrystal thin films and propose a model to elucidate the nonl inear PL behavior. The PL exhibit, an initial decay and a subsequent enhanc ement under continuous excitation, which are attributed to the photodarkeni ng and the effects of photooxidation (neutralization and suppression of the photoionization rate). The PL enhancement correlates with the degree of ox idation. X-ray photoelectron spectroscopy (XPS) confirms that photooxidatio n of nanocrystals proceeds as a function of time.