We report on the enhancement of the photoluminescence ( PL) of poly[ 2-methoxy-5-( 2'-ethylhexyloxy)- p- phenylenevinylene] ( MEH- PPV) by high concentrations of the surfactant tetra- n- octylammonium bromide ( TOABr) in thin films. At constant absorbance intensity, enhancements in the PL of MEH- PPV of a factor of up to 22 were observed. Maximum PL enhancement was observed for thin films containing a molar ratio of 2 mol of TOABr per mole of MEH- PPV monomer units ( 2: 1). In contrast, the absorbance and PL of MEH- PPV and TOABr liquid solutions showed no change as the molar concentration of TOABr changed over 5 orders of magnitude. By imaging the morphology and thickness of the films through confocal fluorescence microscopy and scanning electron microscopy, we observed that maximum PL enhancement was accompanied by the onset of the formation of a lamellar mesophase. Light- emitting devices fabricated from MEH- PPV/ TOABr solutions in an ITO/ PEDOT- PSS/ polymer/ Ca/ Al architecture showed dramatic fall in the quantum efficiency and measured photocurrent as the amount of TOABr in the active layer increased. No electroluminescing activity was observed at molar ratios of 2: 1, indicating that the addition of TOABr impedes charge recombination.