Photoluminescence (PL) emissions from localized trap states in crystalline thin films of quaterthiophene (4T) were investigated. The analysis of the PL spectra as a function of temperature allows to characterize the main trap states involved in the light emission, obtaining their activation energy. From comparison with the data reported for other oligothiophenes (OT) with different number of conjugated rings, a general scheme for the trap-related energy levels is proposed. (C) 2004 Elsevier B.V All rights reserved.