The effects of metallic nanoparticles (NPs) size, excitation wavelength, and fluorescence wavelength on surface plasmon enhanced photoluminescence (PL) have been investigated. The PL of CdSe nanocrystals on Au colloids changes from quenching to enhancement as the size of Au NPs increases from 25 to 45 nm. For the Au NPs larger than 45 nm, the PL enhancement occurs and the enhancement factor is found to be dependent on Au NPs size and excitation wavelength. Besides Au NPs size, the fluorescence wavelength of CdSe nanocrystals is also observed to affect the competition between PL quenching and enhancement. (C) 2010 Elsevier B.V. All rights reserved.