The transmission spectra of thermally evaporated Ga₅₀Se₄₅S₅ films were measured over the wavelength range 300–900 nm. A simple method, suggested by Swanepoel, was used for the determination of the optical constants and thickness of the films. Increasing the thickness of the film beyond 450 nm does not affect the optical constants. The dependence of the absorption coefficient on the photon energy (hν) at the edge of the absorption band is well described by the relation αhν=β(hν−E_opt)² with an optical gap equals 2.4 eV. A good fit of the experimental points with Tauc relation indicates that non-direct transition is the most probable mechanism responsible for the photon absorption inside the investigated film.

Results of differential scanning calorimetric studies on the Mg_0.10As_0.34Se_0.56 chalcogenide glass are reported. The heating rate dependence of the glass transition temperature (T_g), the crystallization onset temperature (T_c) and the crystallization peak temperature (T_p) were studied. These parameters were utilized in the determination of the activation energy of the glass transition (E_g), the activation energy of crystallization (E_c), the Avrami exponent (n) and the frequency factor K₀. E_g was determined from the variation of T_g with the heating rate β and its average value <E_g>=197±5 kJ/mol. E_c was determined using several methods; it gives the average value <E_c>=116±16 kJ/mol. The present investigation indicates that both the glass transition and the crystallization processes occur in a single stage, since the thermograms exhibit a unique value for both T_g and T_p. The crystallization mechanisms for the Mg_0.10 …

The optical absorption behavior has been studied for annealed and illuminated thermally evaporated amorphous GaS thin films. It is observed that photo- and thermally induced effects result in an increase of the optical band gap and the slope parameter of the Tauc plots for these films. The thermally and photo-induced bleaching are ascribed to the suppression of the density of dangling and homo-polar bonds in these films and/or the relaxation process of the disordered state to another relatively high ordered one.

Effect of temperature on the optical absorption spectra and optical parameters is investigated in new synthesized polyester films of poly [oxyiso-phthaloyloxy (2-methoxy-p-phenylene) methylidyne (2-oxo-1, 3-cyclohexanediylidyne) methylidyne (3-methoxy-p-phenylene)](I) and poly [oxysebacoyloxy-(2-methoxy-p-phenylene) methylidene (2-oxo-1, 3-cyclohexanediylidene)-methy-lidene-(3-methoxy-p-phenylene)](II). Absorption measurements are carried out in the temperature range 80–370 K and in the photon energy range 1.9–4 eV. The optical absorption spectra of polymers I and II reveal excitonic absorption bands at 80 and 120 K respectively. These bands are associated with n→ π∗ optical transitions along polymer backbone chains. Analysis of optical absorption data indicates that the Tauc equation for indirect optical transitions successfully explains the optical absorption process in polymeric film I, whereas …

Analysis of the experimental absorption data in GaSe showed that, at low temperature (110 K), intercalation process of sodium atoms, as well as the presence of silicon impurities and native defects such as Ga vacancies and interstitials in a high concentration, result effectively in the broadening of the ground state of the direct exciton and the decrease of exciton peak intensity. On the other hand, increasing temperature leads to the increase of the broadening parameter Λ and a shift of both the position of exciton peaks E_ex, and the band gap E_g toward longer wavelength. These effects can be ascribed to exciton-phonon and exciton-imperfection interactions. Furthermore, acceptable and reasonable values of the temperature coefficient β of the above-mentioned parameters were determined and are equal to +8.64×10⁻⁴, −3.52 × 10⁻⁴ and −3.38 × 10⁻⁴ eVK⁻¹, respectively.

The optical properties of poly [oxyisophthaloyloxy-(2-methoxy-p-phenylene methylidene-(2-oxo-1, 3-cyclohexanediylidene) methylidyne-(3-methoxy-p-phenylene)](I) and poly [oxysebacoyloxy-(2-methoxy-p-phenylene) methylidene-(2-oxo-1, 3-cyclohexanediylidene) methylidene-(3-methoxy-p-phenylene)](II) polymer films were studied. The transmission and absorption measurements were carried out in the energy range 1.9–3.2 eV at 300 K. The data on absorption coefficient versus photon energy were analysed and interpreted in terms of the Tauc model,(α h ̵ ω) 1 2= B 1 2 (h ̵ ω− E opt g). Analysis of experimental results shows that the absorption characteristics give a good fit to the Tauc model, and indicates that both polymers I and II have an indirect band gap. The values of the optical gap E opt g and the slope of the Tauc plots B 1 2 were determined. The study shows that the indirect allowed optical …

Optical properties of poly (oxyisophthaloyloxy (2-methoxy-p-phenylene) methylid-ine (2-oxo-1, 3-cyclohexanediylidene) methylidene (2-methoxy-p-phenylene)) I and poly (oxysebacoyloxy (2-methoxy-p-phenylene) methylidene (2-oxo-1, 3-cyclohex-andeiylidene) methylidene (3-methoxy-p-phenylene)) II polymer films were studied. Transmission and absorption measurements were carried out in the energy range 1.9 to 3.2 eV at 300 K. Absorption coefficient data were analysed and interpreted in terms of the Tauc model (alpha h (cross) w) 1 2/= square root B (h (cross) wE g opt). Analysis of experimental results shows that the absorption characteristics give a good fit to the Tauc model. This indicates that both polymers (I and II) have an indirect band gap. The values of the optical gap E g opt and the slope of Tauc plots square root B were determined. The study shows that the indirect allowed optical transitions are …

Abstract γ irradiation effects on the electrical conductivity behaviour of some new synthesized poly (2, 5-arylidenecyclopentanone)(sample 1), poly (2, 6-arylidenecyclohexanone)(sample 2) and a copolymer (sample 3) have been investigated. Thermal studies over the temperature range 300–500 K showed that the conductivity behaviour follows a two-term Arrhenius-type equation. The first term has a small activation energy which predominates at a lower temperature (extrinsic region) and the second term with a higher activation energy predominates at higher temperatures (intrinsic region). Changes in the activation parameters with the change in the γ-ray dose and the nature of the polymers were discussed. The IR absorption spectra showed a decrease in the intensity of the γ-irradiated sample bands. A mechanism based on the formation of trapped free radicals and their recombination has been suggested …