Unique luminescence properties of rare earth ion-doped polyimide nanoparticles and their mechanism

We prepared the rare earth ion (Eu³⁺, Tb³⁺)-doped polyimide nanoparticles by reprecipitation method. The nanoparticles showed unique luminescence properties. It was observed that luminescence intensity assigned to rare earth ion increased with increase in UV-irradiation time. In contrast, the intensity decreased with elevation of heat-treatment temperature and the luminescence vanished after treatment at 200°C. Broad bands ascribed to a host were observed and these intensities were also varied by UV-irradiation and heat-treatment. The excitation spectra indicated that energy transfer from PI to rare earth ion occurred. The above phenomena are explained that a reversible change in the intensity of luminescence ascribed to a host results in that assigned to rare earth ion through energy transfer.