The temperature evolution of fluorescence spectra was measured to study the behavior of electronic excitation in amorphous naphthalene prepared by vacuum deposition on cold substrates. Monomer- and excimer-type fluorescence was observed in the amorphous state. To study the effect of structural relaxation, spectra were measured by raising the temperature stepwise and also measured at a constant temperature each time after the annealing at different temperatures. No serious structural relaxation was observed if we keep the annealing temperature below the crystallization temperature. From the behavior of the intensities of the monomer and excimer fluorescence, it was found that thermally activated energy transfer is efficient even in the amorphous state. (C) 1998 Published by Elsevier Science B.V. All rights reserved.