Figure 2.

(a) Evolution of photoluminescence (PL) intensity as a function of illumination time for normal PEPI (black scatters) and “heavy” PEPI (magenta scatters). The samples are excited with the 325 nm line of a HeCd laser at 7 mW (corresponding to a fluence 0.175 W·cm⁻²) in air. The PL intensities are normalized to 1 at t = 0 s. The insert graph (b) is the PL spectrum of a 50 nm thick normal PEPI film measured at room temperature. The excitation source for PL measurement is the 325 nm line of a HeCd laser, with an incident power of 0.6 mW (corresponding to a fluence 0.015 W·cm⁻²).