Estimation of the Dispersion and Absorption Parameters of Thermally Evaporated Magnesium Phthalocyanine Thin Films

Magnesium phthalocyanine MgPc thin films are prepared atroom temperature by thermal evaporation technique. The spectralabsorption parameters are determined by applying the molecularorbital theory but the other optical parameters are deduced usingband-model consideration. The optical constants n and k are evaluatedusing spectrophotometric measurements of transmittance andreflectance at nearly normal incidence of light in the wavelength range190-2500 nm. The absorption spectrum recorded in the UV-VISregion shows two absorption bands of phthalocyanine molecule,namely the Soret band (B) and the Q-band. The Q-band shows itscharacteristic splitting (Davydov splitting), and ΔQ is 0.17 eV. Theabsence of a distinct peak near 4.27 eV in MgPc could be due to theabsence of d-electrons of the Mg atoms. The analysis of the spectralbehaviour of the absorption coefficient in the absorption region nearfundamental edge reveal indirect transitions. The fundamental and theonset energy gaps could also be estimated as 2.73 ± 0.01eV and 1.40 ±0.15 eV, respectively, for the as deposited films. From analysis ofdispersion curves, the dielectric constants and other dispersionparameters are also obtained. All previous parameters are obtained foras deposited and annealed films at 350oC for two hours. Discussion ofthe obtained results and comparison with the previously publisheddata are also given.