Luminescence from Nile Red in poly(n-butyl methacrylate)

Films of poly(n-butyl methacrylate) containing the fluorescent dye Nile Red displayed both spontaneous and stimulated luminescence emission. Brief exposure of the dyed film to fluorescent light resulted in a delayed luminescence that decayed in a time scale of minutes and whose intensity was reduced to negligible levels when the film was first cooled to 0 degrees C. The conventional fluorescence lifetime of the dye in the polymer matrix, 5 ns, differed little from the value of 4 ns in ethyl acetate solution. The temperature-dependence (4-35 degrees C) of the lifetime in both media was small. The dyed film also showed spontaneous luminescence that was ascribed to reactions of benzoyl peroxide present as residual initiator and was greatly reduced by prior purification of the polymer. When Nile Red was added to unpurified solvents, the solutions displayed spontaneous luminescence intensities that roughly correlated with the tendency of the solvent to autoxidize.