Photodarkening in Amorphous As2S3 Thin Films

The photodarkening effect in amorphous As2S3 films is studied.The optical absorption edge shifts to a lower energy after illumination ar the bandgap light of 514.5nm wavelength by an argon laser.The shift in well annealed films can be recovered by annealing at 180℃ for 1 h but in un-annealed films it is irreversible.In addition,it was found that the magnitude of photodarkening ΔE increased with the increase of illumination light intensity and illumination time.The reversibility of photodarkening in amorphous As2S3 films can be applied in optical memories.     

Radiation-stimulated changes in the transmission of chalcogenide glasses of As2S3−Ge2S3

The radiative-optical properties of chalcogenide glass-like semiconductors of the As₂S₂−Ge₂S₃ system in the region of a topological 2D-3D-phase transition are investigated. It is shown that γ-irradiation of samples by an absorbed dose of 4.4 · 10⁶ Gy leads to a longwave shift of their optical-transmission edge in the spectrum. The effect observed depends on the structural type of the glasses investigated and changes considerably near the 2D-3D-phase transition. Two components of the transmission-edge shift are detected: a static component, which remains unchanged for a long time after irradiation of the samples, and a dynamic one, which gradually fades in 2–3 months. It is suggested that the microstructural mechanism of these changes is attributable to processes of coordination defect formation in the structural skeleton of the samples. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, pp. 657–660, September–October, 1999.     

Spectroscopic investigations on PbO–As2O3 glasses crystallized with TiO2

PbO–As₂O₃ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy (EDS) techniques. Studies were extended to optical absorption, IR, ESR, luminescence and magnetic susceptibility on these samples. The X-ray diffraction studies reveal the presence of Pb₃O₄, Ti(As₂O₇), Pb(As₂O₆), Pb₃(AsO₄)₂ PbTi₃O₇ and Ti₂O₃ crystal phases. The optical absorption studies together with ESR and magnetic susceptibility measurements indicated that the titanium ions exist in both Ti³⁺ and Ti⁴⁺ states in all the samples and there is an increase in titanium ions in the trivalent state with increasing concentration of nucleating agent TiO₂. The quantitative analysis of these results indicated that there is a growing degree of disorder in the glass network with increasing concentration of the crystallizing agent. The luminescence studies indicated that the samples crystallized with low concentrations of TiO₂ show high luminescence efficiency in the visible region.     

Induced crystallization and the physical properties of PbO–Sb2O3–As2O3: MoO3 glass system

PbO–Sb₂O₃–As₂O₃ glasses mixed with different concentrations of MoO₃ (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy and differential thermal analysis techniques. The X-ray diffraction and the scanning electron microscopic studies have revealed the presence of Pb₅Sb₂O₈, PbSb₂O₆, SbAsO₄, Sb₂MoO₆, Sb₄Mo₁₀O₃₁, As₄Mo₃O₁₅, Pb₅Sb₄O₁₁ crystalline phases in these samples. The differential thermal analysis indicated that the surface crystallization prevails over the bulk crystallization as the concentration of the crystallizing agent is increased. The infrared (IR) spectral studies exhibit bands due to MoO₄ structural units in addition to the conventional bands due to various antimonate and arsenate structural groups. The studies on PbO–Sb₂O₃–As₂O₃: MoO₃ glass-ceramics with respect to various physical properties viz., dielectric properties over a range of frequency and temperature, optical absorption, electron spin resonance (ESR) and magnetic susceptibility at room temperature have also been reported. The optical absorption, ESR and magnetic susceptibility studies indicated that the molybdenum ions exist in Mo⁵⁺ state in addition to Mo⁶⁺ state in these samples. The redox ratio found to increase as the concentration of the MoO₃ is increased. The variations observed in all these properties with the concentration of the crystallizing agent have been analyzed in the light of different oxidation states and environment of molybdenum ions in the glass ceramic network.     

IR impurity absorption in Sb2S3–GeS2(Ge2S3) chalcogenide glasses

The IR optical transmission spectra in the 4000–1000 cm⁻¹ (2.5–10 μm) region in the chalcogenide glasses (ChG) of the ternary Ge–Sb–S system of stoichiometric Sb₂S₃–GeS₂ and non-stoichiometric Sb₂S₃–Ge₂S₃ compositions are studied. The compositional dependences of the measured IR spectra connected with influence of O-, H- and C-based absorbed impurites are analyzed.     

Effect of replacement of Se by S on structural and physical properties of Ge–Sb–As–Se–S chalcogenide glasses

In the present study, the structural and opto-mechanical properties of Ge–Sb–As–Se–S chalcogenide glasses have been investigated. For this purpose, different bulk glasses of Ge₂₀Sb₅As₁₅Se_60?xS_x (0 ≤ x≤50) were prepared by conventional melt quenching technique in quartz ampoule and different characteristics of prepared glasses such as glass transition temperature, density, hardness, transmittance, optical band gap energy and refractive index were determined. The value of hardness and glass transition temperature of prepared glasses were found to increase with increasing the sulfur content as a result of formation of GeS₄ tetrahedral units and increasing the network connectivity and average bonding energy. The optical energy gap (according to Tauc’s relation), transmittance and refractive index of prepared glasses are in direct relation with sulfur content. In this study, the highest value of transmittance (about 70%) and lowest value of refractive index (2–2.3) was achieved in Ge₂₀Sb₅As₁₅Se₄₀S₂₀ and Ge₂₀Sb₅As₁₅Se₁₀S₅₀ glasses, respectively.     

Ultrafast non-resonant third-order optical nonlinearity of GeS2–Ga2S3–CdS chalcogenide glass

Ultrafast third-order nonlinear optical responses of 4(1?x)/5GeS₂-(1?x)/5Ga₂S₃-xCdS (x=0.05, 0.10 and 0.15 in mol%) chalcogenide glasses was investigated by using the femtosecond time-resolved optical Kerr effect technique at a wavelength of 800 nm. The largest third-order nonlinear susceptibility of all samples was estimated to be 1.65×10^?13 esu. An ultrafast nonlinear response time of about 250 fs was observed, which was dominantly assigned to the ultrafast distortion of the electron cloud under femtosecond laser excitation. A nonlinear relationship between the third-order nonlinear susceptibility and the introduced amount of CdS was discussed, suggesting a possible disturbance between different polarizable bonds in the glass system.     

Superconductivity in Hole-Doped （S1-xKx）Fe2As2

A series of layered （Sr1-xKx）Fe2As2 compounds with nominal x = 0-0.40 are synthesized by solid state reaction method. Similar to other parent compounds of iron-based pnictide superconductors, pure SrFe2As2 shows a strong resistivity anomaly near 210 K, which was ascribed to the spin-density-wave instability. The anomaly temperature is much higher than those observed in LaOFeAs and BaFe2As2, the two prototype parent compounds with ZrCuSiAs- and ThCr2Si2-type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe2As2, sharp superconducting transitions at Tc ～ 38 K is observed. We perform the Hall coefficient measurement, and confirm that the dominant carriers are hole-type. The carrier density is enhanced by a factor of 3 in comparison to F-doped LaOFeAs superconductor.     

Elastic moduli and theoretical estimations of physical properties of Ge3Se7–As2Te3

The Bulk (100-x)Ge₃Se₇ - (x)As₂Te₃ (0 ≤ x ≤ 30) glassy alloys were prepared using the melt quenching technique. The elastic moduli (Bulk (K), Micro-hardness (H), Young (Y)), and Poisson's ratio (P_r) of the prepared glasses have been determined using the measured values of the ultrasonic velocities and density (ρ). Values of ρ were measured, then the molar volume (V_m) was estimated theoretically. The DSC thermograms are used to determine the glass transition temperature (T_g). The thermal evaporation method was used to prepare the (100-x)Ge₃Se₇- (x)As₂Te₃ (0 ≤ x ≤ 30) thin films under a vacuum of about 10⁻⁴Pa. The absorbance (A) of the films in the spectral range from 0.45 to 0.85 μm has been measured, then the absorption coefficient (α) and energy gap (E_g) were determined. The Chemical Bond Approach (CBA) has been used successfully to estimate theoretically various physical and structural characteristics of the studied system. Theoretical values of E_g and T_g have been obtained using different methods. The results proved a remarkable agreement between the theoretical and experimental values for both the E_g and T_g. The E_g values decreased from 2.1 to 1.73 eV by increasing the As₂Te₃ content from 0 to 30 at. %. Therefore, these compounds can be used as an absorbing layer for electromagnetic radiation in photovoltaic devices and sensors.     

A computational study of the electron detachment energies of Al2As2 − and Al3As3 −

Ab initio and density functional theory calculations are reported for the low-lying electronic states of Al₂As₂ ^?, Al₂As₂, Al₃As₃ ^?, and Al₃As₃. The ²B_2g ground electronic state of Al₂As₂ ^? has a rhombic structure with the Al atoms occupying the shorter diagonal. In contrast, the As atoms occupy the shorter diagonal of the ground state rhombic structure of Al₂As₂. Electron detachment energies computed for Al₂As₂ ^? are presented and discussed. The adiabatic electron affinity of Al₂As₂ ^? is calculated to be 2.1 eV at the CCSD(T) level, using B3LYP and MP2 optimized geometries. The ground states of both Al₃As₃ ^? (²A₁′) and Al₃As₃ (¹A₁′) have planar hexagonal D_3h geometry. Electron detachment energies computed for the anion are reported. At the CCSD(T)//B3LYP level, the electron affinity of Al₃As₃ is calculated to be 2.47 eV.     

Super-linear frequency dependence of ac conductivity of disordered Ag2S–Sb2S3 at cryogenic temperatures

The ac conductivity of a new class of disordered solids, i.e. mechanochemically synthesized amorphous fast ion conducting Ag₂S–Sb₂S₃ materials, has been investigated in the audio frequency range (10–10⁷?Hz) down to cryogenic temperatures (～10?K). The conductivity spectra exhibit the usual signature of a disordered system at higher temperatures, well described by the Jonscher power law (JPL) i.e., σ′(ω)?=?σ _dc?+?A(T)ω*, although the frequency exponent (n?<?1) is found to be a weak function of temperature. However, as the temperature is lowered, the frequency width of the σ _dc region decreases gradually and that of the JPL region increases. Eventually, the σ _dc region disappears and the JPL region alone dominates the spectrum. However, at the lowest temperatures, both the σ _dc and JPL regions disappear and σ′(ω) obeys a super-linear power law (SPL) (σ′?∝?ω^m , m?≥?1). It is observed that the SPL has strikingly similar characteristics to the well-established nearly-constant-loss (NCL) behaviour corresponding to m?=?1. Both SPL and NCL appear in the same time–temperature (low-temperature/low-frequency) domain. Furthermore, in both cases the conductivity is a distinctly weak function of temperature but quite sensitive to frequency, and the SPL/NCL?→?JPL crossover frequency is thermally activated with almost the same energy as the ac activation energy. The presence of the SPL is further manifested in the form of a well-defined minimum in the dielectric loss, ε″(ω), spectra. It is therefore proposed that the entire low-temperature/low-frequency spectra can be described by a modified Jonscher power law, σ′(ω)?=?σ _dc(T)?+?A(T) ωⁿ ?+?B(T)ω^m , m?=?1 (NCL), m?>?1 (SPL), where the second term with n?<?1 accounts for the JPL and the third term with m?≥?1 accounts for SPL/NCL. The results and some other low-temperature/low-frequency conductivity data are consistent with an asymmetric double well potential (ADWP) model.     

Internal friction in silver-containing (Ag3AsS3) x (As2S3)100 ? x superionic glasses

The mechanical properties of glasses in the Ag₃AsS₃-As₂S₃ system have been studied by the internal friction method. Measurements of internal friction and shear modulus have been carried out in the temperature interval 80?C300 K at deformation frequencies of 10?C50 mHz. Relaxation-type maxima of internal friction have been revealed. It has been shown that the concentration-induced variations in the parameters of the mechanical relaxation process in (Ag₃AsS₃) _x (As₂S₃)_{100 ? x} glasses observed in the region of 20 at % Ag₃AsS₃ are of the threshold character. It has been established that this feature can be associated with the variation in the structural unit, which accounts for the process of mechanical energy dissipation within the temperature interval 150?C250 K.     

Electrical Resistance and Magnetoresistance of Cd3As2–30 mol % MnAs under High Pressures

Physics of the Solid State - The paper presents the results of a study on the Electrical resistance and magneto-resistance (MR) of the composite, consisting of a Dirac semimetal Cd3As2 and 30 mol %...     

Spectroscopic Properties of Er3+/Yb3+-codoped PbO–Bi2O3–Ga2O3–GeO2 Glasses

We investigate the spectroscopic properties of the 1.5-μm emission from the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ions in PbO–Bi₂O₃–Ga₂O₃–GeO₂ glasses for applications in broadband fiber amplifiers. The measured emission peak locates at 1,532 nm with a full width at half-maximum of ∼45 nm. The glasses exhibit a large stimulated emission cross-section of 0.89 × 10⁻²⁰ cm² and a large product of 40.0. Infrared-to-green upconversion occurs simultaneously upon excitation of the 1.5-μm emission with a commercially available 980 nm laser diode. The green-upconversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the ²H_11/2 of Er³⁺. The results indicate the possibility towards the development of lead–bismuth–gallate–germanate based glasses as photonics devices.