Unique luminescence properties of Eu³⁺-doped polyimide

Luminescence properties of Eu³⁺-doped 6FDA-6F polyamic acid (PAA) and polyimide (PI) films were investigated. Eu³⁺-doped PAA films showed a luminescence assigned to Eu³⁺ just after preparation. However, the luminescence intensity decreased with increases in UV-irradiation treatment time. On the other hand, Eu³⁺-doped PI films showed unique luminescence properties. The films showed no luminescence just after preparation. However, the luminescence intensity ascribed to Eu³⁺ increased with increases in the UV-irradiation treatment time. In contrast, the luminescence intensity decreased with elevation of the heat-treatment temperature and disappeared at 220 °C. After the luminescence vanished, the luminescence intensity again increased with increases in the UV-irradiation treatment time. The luminescence of the matrix similarly changed upon UV-irradiation and thermal treatment. It is proposed that luminescence properties of Eu³⁺doped PI films is based on a reversible changes in the luminescence of the matrix caused by UV-irradiation and thermal treatment, resulting in changes in the luminescence of Eu³⁺ due to the energy transfer from the matrix to Eu³⁺.