Spectroelectrochemical experiments on wide-gap semiconductor nanocrystals (ZnSe and Mn2+-doped ZnSe) have allowed the influence of trap electrochemistry on nanocrystal photoluminescence to be examined in the absence of semiconductor band filling. Large photoluminescence electrobrightening is observed in both materials upon application of a reducing potential and is reversed upon return to the equilibrium potential. Electrobrightening is correlated with the transfer of electrons into nanocrystal films, implicating reductive passivation of midgap surface electron traps. Analysis indicates that the electrobrightening magnitude is determined by competition between electron trapping and photoluminescence (ZnSe) or energy transfer (Mn2+-doped ZnSe) dynamics within the excitonic excited state, and that electron trapping is extremely fast (k(trap) approximate to 10(11) s(-1)). These results shed new light on the complex surface chemistries of semiconductor nanocrystals.