On the correlation between the photoluminescence and the optical properties of a thermally-annealed CR-39 polymer-based solid-state nuclear track detector

The induced modifications in the photoluminescence spectra and the optical properties, as well as the correlation between them, of CR-39 polymer-based solid-state nuclear track detectors were investigated after thermal annealing. CR-39 samples were thermally annealed for two hours at different temperatures higher than the glass transition temperature. A linear relationship between the relative mass loss of the CR-39 detector and the annealing temperature was found. The photoluminescence intensity of the pristine CR-39 detector was studied at different excitation wavelengths, where an isosbestic point was observed at 350 nm, which was used as an excitation wavelength. The photoluminescence increased with increasing annealing temperature until temperatures of 200 A degrees C; thereafter, it decreased at temperatures of 220 and 250 A degrees C. Moreover, the wavelength of the photoluminescence emission band was subjected to a red shift that increased with increasing annealing temperature. The optical band gaps, direct and indirect band gaps, were obtained from the optical absorption spectra by using a UV-visible spectrophotometer. The direct and indirect band gaps were found to decrease with increasing annealing temperature. A correlation between the photoluminescence peak wavelength and the optical band gaps was found. The spectral peaks red shifted as both of the optical band gaps decreased. We concluded that the reduction in the optical band gaps for both the direct and the indirect band gaps caused the red shift in the photoluminescence peak of the CR-39 detector.