Optical characterisation of thermally evaporated nickel phthalocyanine thin films

Optical properties of thermally evaporated nickel phthalocyanine thin films have been characterised using spectrophotometric measurements of transmittance and reflectance in spectral range 200-2100 nm. The refractive index n and the absorption index k were calculated. Some of the optical absorption parameters, namely optical absorption coefficient (alpha), molar extinction coefficient (epsilon(molar)), oscillator strength (f), electric dipole strength (q(2)) and absorption half bandwidth (Deltalambda) of the principal optical transitions have been also evaluated. The analysis of the spectral behaviour of the absorption coefficient (alpha), in the absorption region revealed indirect transitions. The fundamental and the onset energy gaps were estimated as 2.77 +/- 0.02 eV and 1.58 +/- 0.01 eV, respectively. According to the analysis of dispersion curves, the dielectric constants and dispersion parameters were obtained. The absorption measurements recorded in the UV-VIS region show two well defined absorption bands of phthalocyanine molecule, namely the Soret band (B) and the Q band. The Q band shows its characteristic splitting (Davydov splitting), and DeltaQ was obtained as 0.21 eV. Discussion of the obtained results and their comparison with the previous published data are also given.