M.A. Osman

VUV reflectivity of LiNbO3 and LiTaO3 single crystals

Near-normal reflectivity and absorption spectra of LiNbO3 and LiTaO3 single crystals in the energy region 0.1–35.0 eV are investigated. Optical functions for the 0–35 eV energy range have been determined by a Kramers-Kronig analysis (including earlier results on the low-energy region). On the basis of the experimental data obtained, the energy transition diagram of LiNbO3 and LiTaO3 is drawn. The BO6-octahedron role is shown to be prominent in the band-structure formation of the crystals studied. Indirect optical transitions in LiNbO3 and LiTaO3 are found at low temperatures (T=6 K).

Thermal annealing and UV irradiation effects on structure, morphology, photoluminescence and optical absorption spectra of EDTA-capped ZnS nanoparticles

Monodispersed ZnS nanoparticles (NPs) were prepared by the chemical precipitation method. Thermally induced structural, morphological and optical changes have been investigated using x-ray diffraction, high-resolution transmission electron microscopy, optical absorption, photoluminescence (PL), and Fourier transform infrared and Raman spectroscopy. It was found that D increases with increasing annealing temperature (T a). The onset of the ZnS phase transition from cubic to hexagonal structure takes place at 400 °C, while cubic ZnS transforms into hexagonal ZnO via thermal oxidation in air at 600 °C. It is also noted that increasing T a results in the red shift of the optical band gap () and the thermal bleaching of exciton absorption. The PL spectrum of as-prepared ZnS nanopowder shows UV emission bands at 363 and 395 nm and blue and green emission at 438 and 515 nm, respectively. With increasing T a up to 500 °C, these bands were quenched and red-shifted. In addition, the UV irradiation effects on colloidal ZnS NPs were investigated. UV irradiation at a dose <13 J cm−2 leads to a decrease in D, the blue shift of and the enhancement of PL intensity. This behavior was explained in terms of surface modification by photopolymerization, the formation of a ZnSO4 passivation layer, as well as the reduction of D by photocorrosion. At a UV irradiation dose <13 J cm−2 both and D did not change and PL intensity was quenched, which were caused by the creation of nonradiative surface states by the photodegradation of the capping agent and photopassivated layer. The mechanism of the PL emission process in ZnS NPs was discussed and an energy band diagram was proposed.

Photoluminescence of barium-strontium niobates and strontium pyroniobate

The photoluminescence (PL) of nominally pure Barium-Strontium Niobates (SBN) with various barium contents, and SBN doped by cerium and Strontium Pyroniobate (SNO) were studied. The investigation included measurements of the spectral characteristic of PL, PL excitation spectra, the temperature dependence of PL intensity, thermoluminescence (TL), the temperature dependence of photoconductivity (PC), and the PL and PC attenuation kinetics.The analysis of the obtained results shows that in these crystals the PL is of an intracentral nature. A model of a luminescent center is suggested.

Influence of sodium intercalation and temperature on the exciton absorption in GaSe

Abstract 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 Eex, and the band gap Eg 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.

Arylidene polymers: 15. Optical band gap and structural relationship of new polyester films of dibenzylidenecyclohexanone

Abstract 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 Eoptg and the slope of the Tauc plots B 1 2 were determined. The study shows that the indirect allowed optical transitions are the predominant transitions in the optical absorption process. From the data a correlation between optical band gap and polymer structure was observed and discussed.

Gamma irradiation effects on the electrical conductivity behaviour and IR absorption spectra of some new synthesized poly(arylidene-cycloalkanones)

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. Differential scanning calorimetry measurements indicated that the crystallization peak changes considerably in magnitude with the increase of the γ-ray dose. This peak almost disappears at higher doses. However the onset of temperature of crystallization ( T c ) decreases with increasing γ-ray dose.

Reversible photodarkening in amorphous Ga20S75Sb5 and Ga20S40Sb40 thin films

Amorphous Ga20S75Sb5 and Ga20S40Sb40 thin films were prepared by thermal evaporation onto clean glass substrates. Transmittance and reflectance measurements were carried out at 300 K, in the wavelength range 400–800 nm, for the virgin and UV illuminated films. Reversible photodarkening is reported for the first time in those films. The photo-induced shift in the non-direct optical energy gap is determined and discussed in the light of current models of photodarkening. The effect of Sb content on the optical band gap and the shift of the absorption edge is also discussed in terms of the coordination number.

Spectroscopic studies and electrical conductivity behavior of γ-irradiated Li2SO4—Na2SO4 mixed system

Abstract The Li2SO4—Na2SO4 mixed system was prepared by the precipitation technique. Electron paramagnetic resonance (EPR) spectra of the γ-irradiated Li2SO4—Na2SO4 mixed system were measured at room temperature. Two types of centers, A and B, identified as SO− 3 and SO− 4, respectively were studied. The SO− 3 center is characterized by an intense isotropic signal with a g-value ≈ 2.0029, while the SO− 4 center appears as a weak and broad signal with a g-value of 2.02. Infrared spectra were recorded for unirradiated and γ-irradiated samples. A decrease in the intensity of the IR spectra was observed after irradiation. The electrical conductivity, σ, was measured for the Li2SO4—Na2SO4 system before and after γ-irradiation in the temperature range from 30 up to 430°C. A considerable decrease in the conductivity value accompanied by an increase in the activation energy was observed after gamma irradiation. The energy of formation of Frenkel defects was estimated to be 3.2eV. The current-voltage characteristics were measured at different temperatures in order to estimate the type of conduction in the samples. Isothermal annealing kinetics were investigated at different temperatures before and after γ-irradiation.

Repair of fistulae in-ano in children using image guided Histoacryl injection after failure of conservative treatment.

PURPOSE Our aim is to determine the feasibility and safety of N Butyl Cyanoacrylate (HISTOACRYL), adhesive material in the treatment of fistula in-ano in infants and children. PATIENTS AND METHODS 30 patients who presented with a perianal fistula (25 males and 5 females) were studied. Their ages ranged from 9 months to 15 years. All patients received medical (conservative) treatment. Six patients improved, 7 patients were subjected to surgical intervention, and the remaining 17 patients were managed by injection of adhesive material through the fistula under fluoroscopic guidance and general anesthesia after failure of medical management. RESULTS Of the 17 children who underwent injection therapy to the fistula in-ano after failed medical management, 14 patients were males. The procedure time was 10 to 15 min. The mean follow up was 18 months. Two patients had a recurrence after one to two months. They were subjected to reinjection, and one of them had a second recurrence. Overall, 16 (94%) of 17 patients have had successful closure of their fistula, and one of them healed from a second injection. CONCLUSION Our method of tissue adhesive Cyanoacrylate injection is safe, feasible, and can be used repeatedly in treatment of fistula in-ano in infants and children.

Optical band gap of K2ZnCl4 single crystals doped with Mn2 in the ferroelectric phase

Absorption edge in the mean crystallographic directions of K2ZnCl4 single crystal doped with Mn2+ was studied at different temperature. The data on absorption coefficient versus photon energy were analysed and could be interpreted in terms of spin-orbit interaction and crystal field splitting. Analysis of absorption spectra indicates that for c- and a-axes, the direct and indirect band gaps were shifted towards the longer wavelength (red shift) with increasing temperature. This behaviour could be interpreted in terms of electron lattice interaction. On the other hand the band gap in b-axis increasing as the temperature increases. This behaviour may be attributed to the weak interatomic interaction. The temperature coefficient of energy gap (δEg/δT) was about 1.3 × 10-3 in both a- and c-axes, while it was in the range of 7.6 × 10-3 eV/K to 2.5 × 10-3 eV/K in the b-axis. A weak impurity absorption band was observed only in b-direction which might be attributed to preference of Mn+2 to align in this direction.