Ultrafast third-order optical non-linearity of 0.56GeS2–0.24Ga2S3–0.2KX(X = Cl, Br, I) chalcohalide glasses by femtosecond Optical Kerr Effect

0.56GeS₂–0.24Ga₂S₃–0.2KX(X = Cl, Br, I) chalcohalide glasses were prepared and their third-order optical non-linearities χ⁽³⁾ have been studied systematically using the femtosecond time-resolved Optical Kerr Effect technique at wavelength of 800 nm. In this system, 0.56GeS₂–0.24Ga₂S₃–0.2KCl glass shows the largest χ⁽³⁾ (1.82 × 10⁻¹³ esu), but 0.56GeS₂–0.24Ga₂S₃–0.2KBr glass has the fastest optical non-linear response time in subpicosecond domain (about 340 fs), which is due to the ultrafast distortion of the electron clouds surrounding the balanced position of Ge, Ga, S, K and Br atoms. The local hyperpolarizability determining non-linear optical response are determined by the partially ionic bonds originating from Ge(Ga)–S bonds and halogen valence bonds. They show great potential applications on the glass-based optoelectronic devices like optical switching.     

Formation,thermal, optical and physical properties of GeS<Subscript>2</Subscript>–Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>–AgCl novel chalcohalide glasses

Novel GeS₂–Ga₂S₃–AgCl chalcohalide glasses had been prepared by melt-quenching technique, and the glass-forming region was determined by XRD, which indicated that the maximum of dissolvable AgCl was up to 65 mol%. Thermal and optical properties of the glasses were studied by differential scanning calorimetry (DSC) and Visible-IR transmission, which showed that most of GeS₂–Ga₂S₃–AgCl glasses had strong glass-forming ability and broad region of transmission (about 0.45–12.5 μm). With the addition of AgCl, the glass transition temperature, Tg decreases distinctly, and the short-wavelength cut-off edge (λ_vis) of the glasses also shifts to the long wavelength gradually. However, the glass-forming ability of the glass has a complicated evolutional trend depended on the compositional change. In addition, the values of the Vickers microhardness, H _v , which decrease with the addition of AgCl, are high enough for the practical applications. These excellent properties of GeS₂–Ga₂S₃–AgCl glasses make them potentially applied in the optoelectronic field, such as all-optical switch, etc.     

Study of thermal and optical properties of GeS2-Ga2S3-Ag2S chalcogenide glasses

Chalcogenide glasses in the GeS₂-Ga₂S₃-Ag₂S pseudo-ternary system were prepared by melt-quenching technique. The structural evolvement of the glasses was studied by Raman spectroscopy. The Raman results show that the addition of Ag₂S involves the breaking of [S₃Ge-GeS₃] ethane-like units and the formation of Ag-S ionic bonds. The results of differential scanning calorimetry (DSC) show that the glasses have relatively high-glass transition temperatures and good thermal stabilities. These GeS₂-Ga₂S₃-Ag₂S glasses have a wide range of transmission approximately from 0.50 to 12.5 μm. In addition, with the method of Maker fringe, SHG was observed in the 0.9GeS₂-0.05Ga₂S₃-0.05Ag₂S glass irradiated by an electron beam. The value of second-order nonlinear optical susceptibility d is as large as 6.6 pm/V, and the poling mechanism of electron beam irradiation was also discussed in this work.     

Unique crystallization and formation of nonlinear optical (Na,K)NbO3 phases in (Na,K)NbGeO5 glasses

Crystalline phases and second-order optical nonlinearities in crystallized glasses of (Na,K)NbGeO₅ (i.e., xNa₂O · (25−x)K₂O · 25Nb₂O₅ · 50GeO₂) are examined. The molar volume of the glasses decreases with increasing Na₂O content, indicating that the glass structure of NaNbGeO₅ glass is more compact compared with KNbGeO₅ glass. The optical basicity of the glasses is 0.94–0.95, implying that chemical bonds among constituents ions are basically very ionic. (Na,K)NbGeO₅ glasses exhibit a unique crystallization depending on the Na₂O/K₂O ratio. The main crystalline phase in crystallized NaNbGeO₅ glass is the NaNbGeO₅ phase. KNbGeO₅ glass shows a prominent bulk nanocrystallization giving nanocrystals of the K_3.8Nb₅Ge₃O_20.4 phase. A glass with the composition of K_3.8Nb₅Ge₃O_20.4 also shows a bulk nanocrystallization. The crystallized glasses with K_3.8Nb₅Ge₃O_20.4 and NaNbGeO₅ crystalline phases do not show a second harmonic generation (SHG) at room temperature. The nonlinear optical (Na,K)NbO₃ phases showing a SHG are formed at the surface (5 μm) of crystallized glasses with x=15 and 20, giving an orientation of the (1 1 0) plane. The present study suggests the presence of mixed-alkali effect in the crystallization behavior of (Na,K)NbGeO₅ glasses.     

Composition dependence of thermally induced second-harmonic generation in chalcohalide glasses

By investigating the second-harmonic generation (SHG) of the series (100 − 2x)GeS₂·xGa₂S₃·xPbI₂ (x = 5, 10, 15, and 20) chalcohalide glass samples after thermal poling, it was found that there was an optimal poling temperature for each composition and there was also a relation between optimal poling temperature and glass transition temperature. With increasing x, the obtained second-order susceptibility χ⁽²⁾ shows an increase first and then decrease, and the maximum was seen at x = 15. A dipole reorientation model and structural relaxation causing by Ga₂S₃ and PbI₂ were proposed to explain the dependence of poling temperature on SH intensity for each composition and the presence of the maximum χ⁽²⁾ in this chalcohalide glass series.     

Preparation of SrAl2O4: Eu, Dy nanometer phosphors by detonation method

SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer phosphors were synthesized by detonation method. The particle morphology and optical properties of detonation soot that was heated at different temperatures (600–1100 °C) had been studied systematically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer powders in monoclinic system (a = 8.442, b = 8.822, c = 5.160, β = 93.415) can be synthesized by detonation method, when detonation soot was heated at 600–800 °C. The particle size of SrAl₂O₄: Eu²⁺, Dy³⁺ is 35 ± 15 nm. Compared with the solid-state reaction and sol-gel method, synthesis temperature of the detonation method is lower about 500 and 200 °C respectively. After being excited under UN lights, detonation soot and that heated at 600–1100 °C can emit a green light.     

Synthesis and characterization of nanocrystalline manganese pyrophosphate Mn2P2O7

Mn₂P₂O₇ polyhedral particles were synthesized by simple and cost-effective method using manganese nitrate hydrate and phosphoric acid in the presence of nitric acid with further calcinations at the temperature of 800 °C. The crystallite size obtained from X-ray line broadening is 31 ± 13 nm for the Mn₂P₂O₇. The X-ray diffraction and SEM results indicated that the synthesized nanoparticles have only the structure without the presence of any other phase impurities. The FT-IR and FT-Raman spectra show characteristic bands of the P₂O₇⁴⁻ anion. The UV–Vis–NIR spectrum confirms the octahedral coordination of Mn²⁺ ion.     

Glass formation and properties of novel GeS2-Sb2S3-In2S3 chalcogenide glasses

Novel chalcogenide glasses based on GeS₂-In₂S₃-Sb₂S₃ system were prepared by conventional melt-quenching method and their physicochemical properties, e.g. glass transition temperature, density, and Vickers micro-hardness, were studied in detail. The results show that the thermal, mechanical, and optical properties depend largely on four-coordinated Ge or In entities and are sensitive to the variation of the connectivity in the GeS₂-In₂S₃-Sb₂S₃ glass network. It is a promising chalcogenide glass system suitable for rare earth doping or crystallization of rare earth doped crystals, which aims at optical applications of IR optical amplifier or efficient solid state laser.     

Synthesis and characterization of LiCo0.3−xGaxNi0.7O2 (x = 0, 0.05) as a cathode material for lithium ion battery

The single phase of LiCo_0.3−xGa_xNi_0.7O₂ (x = 0, 0.05) was synthesized by a sol–gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The powders are homogeneous and have a good-layered structure. The synthesized LiCo_0.25Ga_0.05Ni_0.7O₂ exhibits better electrochemical performance with an initial discharge capacity of 180.0 mAh g⁻¹ and a capacity retention of 95.2% after 50 cycles between 2.8 and 4.4 V at 0.2C rate. The study on the structural evolution of the material during the cycling shows that Ga-doping improves the structure stability of LiCo_0.3Ni_0.7O₂ at ambient temperature and 55 °C. Meanwhile, Ga-doping not only suppresses the alternating current (AC) impedance of LiCo_0.3Ni_0.7O₂ but also promotes the Li⁺ diffusion in LiCo_0.3Ni_0.7O₂. Furthermore, thermal stability of the charged LiCo_0.25Ga_0.05Ni_0.7O₂ is improved, which may be attributed to the retard of O₂ evolution in LiCo_0.3Ni_0.7O₂ and the suppression of electrolyte oxidation during cycling by Ga-doping_.     

Emissions properties of Ho: I7 → I8 transition sensitized by Er and Yb in fluorophosphate glasses

Emission properties of Ho³⁺ at 2.0 μm and the energy transfer mechanism between Yb³⁺, Er³⁺ and Ho³⁺ ions in fluorophosphate glasses are investigated. The measured emission spectra show that the ⁵I₇ → ⁵I₈ transition of Ho³⁺ upon 980 nm laser diode excitation is strong. Judd–Ofelt intensity parameters (Ω_λ, λ = 2, 4, 6), spontaneous transition probability (A_rad), radiative lifetime (τ_r), absorption cross section (σ_a), stimulated emission cross section (σ_e) and FWHM ×  for the transition of Ho³⁺: ⁵I₇ → ⁵I₈ are calculated and discussed. The obtained results show that the present Yb³⁺/Er³⁺/Ho³⁺ triply-doped fluorophosphate glass can be identified to be a promising material at 2.0 μm emission.     

Microwave dielectric and elastic properties of glass-added Ba6−3xR8+2xTi18O54 (x = 2/3)

Microwave dielectric properties of Ba_6−3xSm_8+2xTi₁₈O₅₄ (x = 2/3) [BST] ceramics with the addition of 0–3 wt.% of various glasses have been studied. It has been found that the addition of 0.5 wt.% of the glasses decreases the sintering temperature by about 150 °C. In general, addition of 0.5 wt.% of Zn, Mg and Pb-based glasses deteriorate the quality factor, whereas aluminum and barium borosilicates do not decrease it considerably. The quality factor and dielectric constant decrease with increasing amount of glass. The temperature coefficient of resonant frequency shifts towards positive or negative depending on the composition of the glass. A glass–ceramic composite with a dielectric constant 64, Q × f nearly 8500 GHz and near to zero τ_f could be obtained at a sintering temperature of 1175 °C when 3–4 wt.% Al₂O₃–B₂O₃–SiO₂ glass was added to BST ceramic. The Young's modulus decreases with increasing amount of glass, irrespective of the composition of glass.     

Optical bistability for ZnO–Nb2O5–TeO2 glasses

We examined the optical nonlinear properties of ZnO–Nb₂O₅–TeO₂. The absorption and Raman spectra were measured, the third-order nonlinear susceptibility was determined by degenerated four wave mixing technique. The magnitude of χ⁽³⁾ is about 1.0 × 10⁻¹² esu, larger than that of silica glasses, and the optical bistability was observed in a Fabry–Perot cavity.     

Microwave dielectric properties and sintering behavior of nano-scaled (α + θ)-Al2O3 ceramics

The dielectric properties at microwave frequencies and the microstructures of nano (α + θ)-Al₂O₃ ceramics were investigated. Using the high-purity nano (α + θ)-Al₂O₃ powders can effectively increase the value of the quality factor and lower the sintering temperature of the ceramic samples. Grain growth can be limited with θ-phase Al₂O₃ addition and high-density alumina ceramics can be obtained with smaller grain size comparing to pure α-Al₂O₃. Relative density of sintered samples can be as high as 99.49% at 1400 °C for 8 h. The unloaded quality factors Q × f are strongly dependent on the sintering time. Further improvement of the Q × f value can be achieved by extending the sintering time to 8 h. A dielectric constant (_r) of 10, a high Q × f value of 634,000 GHz (measured at 14 GHz) and a temperature coefficient of resonant frequency (τ_f) of −39.88 ppm/°C were obtained for specimen sintered at 1400 °C for 8 h. Sintered ceramic samples were also characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Computational investigation of GanAl (n = 1–15) clusters by the density-functional theory

Low-lying equilibrium geometric structures of aluminum-doped gallium cluster Ga_nAl (n = 1–15) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied with the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee–Yang–Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static polarizabilities are calculated for the ground-state structures within the same method. The growth pattern for Ga_nAl (n = 1–15) clusters is Al-substituted Ga_n + 1 clusters and it keeps the similar frameworks of the most stable Ga_n + 1 clusters except for Ga₈Al and Ga₁₃ Al clusters. The Al atom substituted the surface atom of the Ga_n + 1 clusters for n < 12. Starting from n = 12, the Al atom completely falls into the center of the Ga-frame. The Al atom substituted the center atom of the Ga_n + 1 clusters to form the Al-encapsulated Ga_n geometries for n > 12. The odd−even oscillations from Ga_nAl (n = 5) in the dissociation energy, the second-order energy differences, the HOMO–LUMO gaps, the ionization potential, the electron affinity, and the hardness are more pronounced. The stability analysis based on the energies clearly shows the clusters from n = 5 with an even number of valence electrons are more stable than clusters with odd number of valence electrons.     

Visible to mid-infrared supercontinuum generated in novel GeS2–Ga2S3–CsI step-index fibre

In this work, two kinds of GeS₂–Ga₂S₃–CsI chalcogenide glasses had been fabricated in conventional meltquenching method, and these glasses express excellent transmittance (0.52–10.5?µm), low refractive index difference, high Raman gain and good thermal stability against crystallization. We designed a highly nonlinear step-index fibre consisting of a 72GeS₂–18Ga₂S₃–10CsI core and a 73GeS₂–15Ga₂S₃–12CsI cladding with the zero dispersion wavelength in near-infrared (<1?µm), and theoretically analysed the optical and nonlinear characteristics of this fibre in detail. Substantial simulation results revealed that wide ultra-flat supercontinuum broadening from the visible to the mid-infrared range can be achieved by pumping this fibre at 1064?nm.     

Microstructure and mechanical properties of an HfB2 + 30 vol.% SiC composite consolidated by spark plasma sintering

An ultra-high-temperature HfB₂–SiC composite was successfully consolidated by spark plasma sintering. The powder mixture of HfB₂ + 30 vol.% β-SiC was brought to full density without any deliberate addition of sintering aids, and applying the following conditions: 2100 °C peak temperature, 100 °C min⁻¹ heating rate, 2 min dwell time, and 30 MPa applied pressure. The microstructure consisted of regular diboride grains (2 μm mean size) and SiC particulates evenly distributed intergranularly. The only secondary phase was monoclinic HfO₂. The incorporated SiC particulates played a key role in enhancing the sinterability of HfB₂. Flexural strength at 25 °C and 1500 °C in ambient air was 590 ± 50 and 600 ± 15 MPa, respectively. Fracture toughness at room temperature (RT) (3.9 ± 0.3 MPa √m) did not decrease at 1500 °C (4.0 ± 0.1 MPa √m). Grain boundaries depleted of secondary phases were fundamental for the retention of strength and fracture toughness at high temperature. The thermal shock resistance, evaluated through the water-quenching method, was 500 °C.     

Oxidation characteristics of Ti3AlC2 over the temperature range 500–900 °C

Titanium aluminium carbide (Ti₃AlC₂) displays a unique combination of characteristics of both metals and ceramics coupled with an unusual combination of mechanical, electrical and thermal properties. In this research, the oxidation characteristics of Ti₃AlC₂ over the temperature range 500–900 °C were studied by synchrotron radiation diffraction (SRD) and secondary-ion mass spectrometry (SIMS) experiments which provided elemental and phase compositional depth profiles over this range. Evidence for the outward diffusion of Al during oxidation was shown for the first time by the complementary SIMS results, which suggested the existence of amorphous Al or aluminium oxide at low temperature oxidation. At 500 °C, only anatase-TiO₂ was detected by SRD in addition to the parent Ti₃AlC₂. Transformation of anatase to rutile was observed at 600 °C and was completed by 900 °C. The crystalline phase α-Al₂O₃ was detected at 900 °C but not at lower temperatures.     

Study on structural phase transitions and relaxation processes of Cs2Co(SO4)2·6H2O and Cs2Zn(SO4)2·6H2O crystals

The structural phase transitions and relaxation processes of Cs₂Co(SO₄)₂·6H₂O and Cs₂Zn(SO₄)₂·6H₂O single crystals were investigated, with the phase transitions of both crystals being determined from NMR data. The spin–lattice relaxation time, T₁, of the ¹³³Cs nucleus in two crystals undergoes a significant change near the phase transition temperature, T_C, and these changes coincide with the changes in the splitting of the ¹³³Cs resonance lines. The variations in the temperature dependence for the splitting of the ¹³³Cs resonance lines and T₁ near T_C are related to changes in the symmetry of surrounding Cs⁺. In addition, the ¹³³Cs T₁ of Cs₂Co(SO₄)₂·6H₂O, which contains paramagnetic ions, was found to be shorter than that of Cs₂Zn(SO₄)₂·6H₂O. This relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ions. The differences between the ¹³³Cs T₁ of these compounds are probably due to the differences between the electronic structures of their metal ions.     

Growth, thermal and spectroscopic characteristics of LiNd(WO4)2 crystal

Crystal growth, thermal and optical characteristics of LiNd(WO₄)₂ crystal have been investigated. The LiNd(WO₄)₂ crystal up to Ø15 × 32 mm³ has been grown by Czochralski technique. The hardness is about 5.0 Mohs’ scale. The specific heat at 50 °C is 0.42 J g⁻¹ K⁻¹. The thermal expansion coefficient for c- and a- axes is 1.107 × 10⁻⁵ and 2.104 × 10⁻⁵ K⁻¹, respectively. The absorption and fluorescence spectra and the fluorescence decay curve of LiNd(WO₄)₂ crystal were measured at room temperature. Some spectroscopic parameters such as the intensity parameters, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and emission cross sections were estimated.     

χ measurements and optical limiting studies of 2-chloro-5-nitro-N′-[(1E)-phenylmethylidene] benzohydrazide with substituents

The nonlinear optical properties of hydrazones substituted with different donor groups were studied using single beam Z-scan technique with nanosecond laser pulses at 532 nm. The nonlinear response in these molecules was found to increase with increase in the donor strength of the substituted group. The χ⁽³⁾ value of these molecules is found to be of the order of 10⁻¹³ esu. The nonlinear refractive index (n₂) of the samples is found to be negative and the largest value of n₂ obtained for the strong donor-substituted molecule is −8.83 × 10⁻¹¹ esu. All samples show good optical limiting behavior at 532 nm. The best optical limiting behavior was observed with the molecule substituted by a strong electron donor.