Damage and recovery processes for the luminescence of irradiated PEN films

The degradation and recovery of the optical emission characteristics of polyethylene naphthalate (PEN) films were studied during irradiation with MeV protons and UV photons. The photo-stimulated luminescence (PL) consisting of two major peaks decreased with the incident energy fluence, particularly for ion irradiation. At the beginning of irradiation, the rate of reduction of the PL intensity in the UV-irradiated film was comparable to that for ion irradiation, but the residual PL intensity in the UV-irradiated film was considerably larger at higher fluences. In addition, no change in the PL characteristics of the UV-irradiated film was observed after stopping the UV irradiation, indicating that the damage caused by the UV photons was permanent. However, the PL intensity from the ion irradiated film increased immediately when the film was exposed to air. The recovery of the luminescence centers in the ion-irradiated PEN film is attributed to ion-induced surface modification, which plays a role in the enhancement of the dissociation of water molecules and the diffusion process for constituent atoms.