Effect of dopant on the intrinsic properties of some multifunctional aromatic compounds films for target applications

摘要

UV-VIS transmission and fluorescence spectroscopy have been used to study some intrinsic properties of crystalline films of pure meta-dinitrobenzene (/re-DNB) and, pure and doped benzil. We have evaluated the band gap energy, E_g = 2.92 eV, emphasising the near classical semiconductor behaviour of m-DNB. The two bands split of the (n, pi*) level is assumed to be the origin the two edges absorption in benzil films with the energetic thresholds at E-(g1) = 2.84 eV and E_(g2) = 3.55 eV. The red shift of the emission peak in m-DNB films has been correlated with the process of self-absorption of the emitted radiation in the thicker film. The effect of the impurities on the shape and position of the emission peaks in benzil has been investigated and we have observed no significant shift of the absorption peak situated at 3.25 eV. We also have identified a three steps process for the relaxation of the excited crystalline lattice of benzil involving the geometrical change of the (S i) excited state, the intersystem crossing and the radiative decay by phosphorescence with a peak at 2.30 eV. The small blue shift of this emission peak in benzil highly doped with sodium has been attributed to the modification of the molecular geometry of benzil as a result of the change in the trans-planar molecular configuration induced by the chemical reaction between the atoms of alkali metal and the carbonyl groups.