Passive Q-switching performance of intracavity frequency-doubled red laser with mixed Nd:GdxY1−xVO4 crystals

Passive Q-switching laser operation of Nd:Gd_xY_1−xVO₄ mixed crystals at 671 nm has been compared in the same V-shape folded cavity. Based on our comparative analysis, the best laser characteristics - the highest pulse energy and peak power and the shortest pulse width - were demonstrated by Nd:Gd_0.63Y_0.37VO₄ crystal. At the same time, this crystal possesses the lowest thermal conductivity in comparison with the other Nd:Gd_xY_1−xVO₄ crystals, which could result in decreasing the average laser output power. To verify this assumption we also measured the focal lengths of thermal lens induced in the crystals during the laser operation.     

Mechanical and environmental properties of Ge1−xCx thin film

Ge_1−xC_x thin film was prepared by plasma-enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ as precursors and its mechanical and environmental properties were investigated. The samples were measured by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum, FT-IR spectrometer, WS-92 testing apparatus of adhesion and FY-03E testing apparatus of salt and fog. The results show that the infrared refractive index of Ge_1−xC_x thin film varies from 2 to 4 with different x values. The adhesion increases with increasing gas flow ratio of GeH₄/CH₄ and decreases with increasing film thickness. The nanoindentation hardness number decreases with increasing germanium content. Three series films exhibit the best anti-corrosion property when the RF power is about 80 W, or substrate temperature is about 150 °C, or DC bias is about −100 V. Furthermore, increasing the gas flow ratio of GeH₄/CH₄ improves the anti-corrosion property of these films.     

Antireflective characteristics of Ge1−xCx films on sub-wavelength structured ZnS surfaces

Antireflective sub-wavelength structures (SWSs) combined a Ge_1−xC_x coating on Zinc sulfide (ZnS) can enhance the long-wave infrared transmission and durability of ZnS, which have the potent for practical applications. We have investigated the antireflective characteristics of Ge_1−xC_x sub-wavelength periodic hole structures on ZnS through the Fourier modal method (FMM) for application with normally incident, randomly polarized, 10.6 μm wavelength. Then according to the results, we have successfully fabricated the sub-wavelength periodic square hole structures with Ge_0.05C_0.95 films on one side of ZnS. A substantial transmittance improvement for bare ZnS in the 8-12 μm spectral region was obtained.     

Influence of electron irradiation on characteristics of Si1−xGex p-n-structures

Electrically active defects induced by irradiation with 4 MeV electrons and their influence on dynamic and static parameters of p-n-structures with bases on boron doped Si_1−xGe_x alloys (0<x?0.06) have been investigated. It has been found that after irradiation with the electron fluence Φ=2×10¹⁴ cm⁻² lifetime of minority charge carriers decreases more than 12 times and forward voltage increases twice. Deep level transient spectroscopy (DLTS) studies have shown that interstitial carbon atoms are dominant electrically active defects induced by the irradiation. These defects are transformed into the complexes “interstitial carbon—interstitial oxygen” upon annealing of irradiated samples in the temperature range 50-100 °C.     

Chemical bonding of a-Ge1−xCx:H films grown by RF reactive sputtering

Amorphous hydrogenated germanium-carbon (a-Ge_1−xC_x:H) films were deposited by RF reactive sputtering pure Ge (1 1 1) target at different flow rate ratios of CH₄/(CH₄+Ar) in a discharge Ar/CH₄, and their composition and chemical bonding were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). XPS and FTIR results showed the content of germanium in the films decreased with the increase of the flow rate ratio CH₄/(Ar+CH₄), and the Ge-C, Ge-H, C-H bonds were formed in the films. The fraction of Ge-C, Ge-H, and C-H bonds was strongly dependent on the flow rate ratio. Raman results indicated that the films also contain both Ge-Ge and C-C bonding. Based on the change of the chemical bonding of a-Ge_1−xC_x:H films with the flow rate ratio CH₄/(CH₄+Ar), an optimal experimental condition for the application of infrared windows was obtained.     

The influence of ambient conditions on properties of MgxZn1−xO films by sputtering

The Mg_xZn_1−xO films were prepared in different Ar-O₂ mixture ambience by magnetron sputtering. According to the X-ray diffraction (XRD) patterns and the energy dispersive X-ray spectroscopy (EDS) results, it was found that the Mg contents in the films varied with the different ratios of O₂/O₂+Ar, and the crystal quality of the films improved with the increasing of Mg contents. Meanwhile, the ultraviolet and visible (UV-vis) absorption spectroscopy indicated that the band gap of the films also increased. Moreover, it could be seen that the photoluminescence (PL) spectrum was different from that of undoped Zinc oxide (ZnO) films or the results in other reports on the Mg_xZn_1−xO films: there was no blueshift effect happening for the near-band-edge (NBE) emission in Mg_xZn_1−xO films with different Mg contents.     

Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

Regulate the content of magnesium in MgxZn1−xO films by vacuum anneal

Mg_xZn_1−xO thin films were grown on c-sapphire substrates by metal-organic chemical vapor deposition (MOCVD), followed by annealing in vacuum at different temperatures for 1 h. The UV emission peak was blue shifted in the photoluminescence (PL) spectra and a dramatic shift of (0 0 2) diffraction peak to higher angle was observed in X-ray diffraction (XRD) pattern with increasing anneal temperature. This suggested the band gap and the lattice parameter of Mg_xZn_1−xO had been affected by annealing in vacuum. Furthermore, the structure of the film became sparser due to annealing in vacuum. From the X-ray photoelectron spectroscopy (XPS) and ICP of the Mg_xZn_1−xO film, we can find that the anneal temperature have an effect on the content of each element in Mg_xZn_1−xO quantitatively. In addition, the value of x in Mg_xZn_1−xO varied slightly as the annealing temperature increased. The above phenomena indicated that annealing in vacuum could slightly adjust the percentage of Mg indirectly in Mg_xZn_1−xO film and offer a good idea in Mg_xZn_1−xO devices facture.     

Influence of Se on the electron mobility in thermal evaporated Bi2(Te1−xSex)3 thin films

Thermoelectric solid solutions of Bi₂ (Te_1−xSe_x)₃ with x = 0, 0.2, 0.4, 0.6, 0.8 and 1 were grown using the Bridgman technique. Thin films of these materials of different compositions were prepared by conventional thermal evaporation of the prepared bulk materials. The temperature dependence of the electrical conductivity σ, free carriers concentration n, mobility μ_H, and seebeck coefficient S, of the as-deposited and films annealed at different temperatures, have been studied at temperature ranging from 300 to 500 K. The temperature dependence of σ revealed an intrinsic conduction mechanism above 400 K, while for temperatures less than 400 K an extrinsic conduction is dominant.The activation energy, ΔE, and the energy gap, E_g, were found to increase with increasing Se content. The variation of S with temperature revealed that the samples with different compositions x are degenerate semiconductors with n-type conduction. Both, the annealing and composition effects on Hall constant, R_H, density of electron carriers, n, Hall mobility, μ_H, and the effective mass, m^∗/m₀ are studied in the above temperature range.     

Enhanced ferromagnetic properties of multiferroic BiCoxFe1 − xO3 synthesized by hydrothermal method

The BiCo_xFe_1 − xO₃ samples have been successfully synthesized by hydrothermal process. The resulting products were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray (EDS), differential thermal analysis (DTA), and physical property measurement system (PPMS).It was found that the magnetization of the obtained products was greatly enhanced by Co substituting for Fe ions. Furthermore, the value of magnetism of BiCo_xFe_1 − xO₃ samples can be adjusted by Fe doping concentration. DTA curve indicates the ferroelectric properties of the obtained BCFO samples are not affected by Co substitution. Therefore, it would be interesting to realize thin films with similar compositions and study their properties in the interest of device applications.     

White upconverted luminescence of Ho/Yb/Tm tri-doped Gd2Mo3O9 phosphors

Yb³⁺/Tm³⁺/Ho³⁺ tri-doped Gd₂Mo₃O₉ phosphors were synthesized by the high-temperature solid-state method. Under 980 nm near-infrared excitation, the white-light emission can be observed, which is consists of the blue, green, and red UC emissions. The green and red emission at 547 nm and 660 nm originated from the transition of Ho³⁺ (⁵S₂, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈) and the blue emission at 475 nm attributed to the transition of Tm³⁺ (⁵G₄ → ⁵H₆). In this experiment, we selected the optimum concentration ratio of the three rare earths for the bright white emission. The Commission internationale de L’Eclairage (CIE) coordinates for the samples were calculated, and chromaticity coordinates were very close to white light regions. We find that the calculated CIE color coordinates of the Yb³⁺/Tm³⁺/Ho³⁺ tri-doped Gd₂Mo₃O₉ phosphors changed with the incident pump power from 400 mW/cm² to 1000 mW/cm². The upconversion luminescence mechanism of the samples was discussed on its spectral. The white light may be proved to be a candidate material for applications in various fields.     

Tuning the optical properties of alloyed CdSexS1 − x nanoparticles by changing the constituent stoichiometry

The spherical particles CdSe_xS_1 − x with 30-80 nm in radius have been successfully prepared by the hydrothermal reaction at 200 °C. The structure characterization which has been carried out using X-ray diffraction (XRD) shows hexagonal crystal structure. Novel properties have been observed via UV-visual absorption spectra and photoluminescence (PL) spectra. The absorption shoulder and the luminescence emission peaks have been tuned by changing the mole ratio of Se in the CdSe_xS_1 − x samples.     

Structure and thermal conductivity of Gd2(TixZr1 − x)2O7 ceramics

The Gd₂(Ti_xZr_1 − x)₂O₇ (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd₂(Ti_xZr_1 − x)₂O₇ were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd₂(Ti_xZr_1 − x)₂O₇ from room temperature to 1400 °C was measured by a laser-flash method. The Gd₂Zr₂O₇ has a defect fluorite-type structure; however, Gd₂(Ti_xZr_1 − x)₂O₇ (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd₂Zr₂O₇ and Gd₂Ti₂O₇ are infinitely soluable. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ is within the range of 1.33 to 2.86 W m^− 1 K^− 1 from room temperature to 1400 °C.     

Dye-sensitized solar cells composed of Ti1−xSnxO2 nanocrystals

Ti_1−xSn_xO₂ nanocrystals were successfully synthesized by using a simple solvothermal route, and its band energy gap broaden and flat band potential can be rationally regulated with increasing x value. Furthermore, Ti_1−xSn_xO₂ nanocrystals were first used as the photoelectrode material for dye-sensitized solar cells. A cell made of Ti_1−xSn_xO₂ (x = 0.3) exhibited the best photovoltaic performance. This is due to its most narrow band gap energies, most negative flat band potential and lowest dark current densities. After the surface of Ti_1−xSn_xO₂ (x = 0.3) electrode was treated with TiCl₄ solution, the cell sensitized by a mixed solution of N719 and D131 dye exhibited the best efficiency of 4.64% under the illumination of 1 sun (AM1.5, 100 mW cm⁻²).     

Electrical properties of lead-free thick film NTC thermistors based on perovskite-type BaCoxCo2xBi1 − 3xO3

Lead-free thick film negative temperature coefficient (NTC) thermistors based on perovskite-type BaCo^II_xCo^III_2xBi_1 − 3xO₃ (x ≤ 0.1) were prepared by mature screen-printing technology. The microstructures of the thick films sintered at 720 °C were examined by X-ray diffraction and scanning electron microscopy. The electrical properties were analyzed by measuring the resistance-temperature characteristics. For the BaBiO₃ thick films, the room-temperature resistivity is 0.22 MΩ cm, while the room-temperature resistivity is sharply decreased to about 3 Ω cm by replacing of Bi with a small amount of Co. For compositions 0.02 ≤ x ≤ 0.1, the values of room-temperature resistivity (ρ₂₃), thermistor constant (B_25/85) and activation energy are in the range of 1.995-2.975 Ω cm, 1140-1234 K and 0.102-0.111 eV, respectively.     

Controlling temperature coefficient of resistivity in La1−xSrxMnO3 ceramics

We propose La_1−xSr_xMnO₃ as a new lead-free and ruthenium-free conductive oxide used for thick film resistors. The temperature coefficient of resistivity (TCR) of the La_1−xSr_xMnO₃ was controlled systematically by changing the composition x. The TCR behavior depended on the change of the crystal symmetries and the average valence of Mn ions. The highest value of 9356 ppm/°C was obtained at the x = 0.35. Zero TCR was realized around 0.200 < x < 0.225 and 0.45 < x < 0.50, where the critical x values were related to the characteristic change from Mott-insulator to metallic behavior. The systematical controlling TCR and the zero TCR are the first to be demonstrated for conductive oxide.     

Structural and photocatalytic properties of TiO2/SiOx/TiOx multi-layer prepared by electron-beam evaporation method

TiO₂/SiO_x/TiO_x multi-layers on quartz glass were prepared by electron-beam evaporation method and their structural and photocatalytic properties were investigated. The photocatalytic activity of the TiO₂/SiO_x/TiO_x multi-layer was evaluated by the photodecomposition of methylene blue in aqueous solution. As the thickness of the SiO_x inter-layer increased, the surface roughness of the TiO₂/SiO_x/TiO_x multi-layer increased but the anatase crystallite size decreased. The TiO₂/SiO_x(80 nm)/TiO_x multi-layer exhibited excellent photocatalytic activity resulting from higher surface roughness and more trap levels in the SiO_x(80 nm) inter-layer.     

Preparation of (ZnO)1−x(GaN)x:Mn powder and its photoluminescence properties

(ZnO)_1−x(GaN)_x:Mn²⁺ powder was prepared by a conventional solid-state reaction under an NH₃ gas flow. The sample preparation conditions including the mixing ratio of the raw materials, the annealing temperature, and the annealing time were varied. The crystallinity and the photoluminescence (PL) intensity of this fluorescent material were improved by increasing the amount of ZnO and by increasing the annealing time, and no changes was observed in the PL wavelength. The crystallinity of the samples was enhanced and the PL intensity increased markedly at annealing temperatures of 700 °C and 800 °C, respectively. Moreover, it was clarified that the sample could be synthesized at annealing temperatures of above about 650 °C.     

Polymer-assisted synthesis and luminescence properties of MgAl2O4:Tb nanopowder

In the present work, terbium doped magnesium alluminate (MgAl₂O₄:Tb) nanopowder was synthesized by a polyacrylamide gel method. Structure, morphology and luminescence spectra were investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL) measurements. The results showed that the single-phase MgAl₂O₄ could be formed at a relatively low temperature about 800 °C without unreacted Al₂O₃ and MgO phases. Powders with nanosized microstructures were formed. The polyacrylamide gel method resulted in a powder with smaller particle size and fewer agglomerates than the conventional sol-gel method. Luminescence analysis indicated that, the prepared MgAl₂O₄:Tb powders had strong green emission with ⁵D₄-⁷F₅ as the most prominent group. The emission intensity increased with increasing the calcination temperature.