A facile low temperature hydrothermal route to CdSO4 nanotubes/rods

Cadmium sulphate nanotubes/rods have been synthesized by hydrothermal treatment using CdSO₄ powder as precursor and hexadecylamine (HDA) as surfactant at 180 °C for 7 days. The powder X-ray diffraction (PXRD) pattern reveals that the CdSO₄ nanotubes/rods are of orthorhombic phase. Fourier transform infrared (FTIR) spectrum shows characteristic bands due to the sulfate ion in 1114 cm^? 1 and 617 cm^? 1 region, besides bands due to the amine moiety. Transmission electron micrograph (TEM) images reveal the nanorods are of 10–15 nm in thickness and nanotubes of wall thickness 5–8 nm. UV–visible absorption spectrum of CdSO₄ nanotubes/rods shows the peak at 221 nm. Photoluminescence (PL) spectrum exhibits an intense UV band at 372 nm and weak green band at 484 nm.     

Infrared and Structural Properties of Y1−xNdxBa2Cu3O7−δ (0 ≤ x ≤ 1)

Infrared and structural properties of Y_1?x Nd _x Ba₂Cu₃O_7?δ (0 ≤ x ≤ 1) were investigated using infrared absorption spectroscopy and X-ray powder diffraction. The unit cell parameters of the samples were defined using X-ray diffraction data. The resistance measurements showed that the samples revealed superconductivity in the temperature range of 80–100 K. It was observed that by the substitution of Nd to Y in YBa₂Cu₃O_{7 ? δ} IR band at 573 cm^?1 that is assigned as Cu–O axial antisymmetric stretching mode shifts to 533 cm^?1 while the band at 620 cm^?1 that is due to Cu–O symmetric stretching mode in YBa₂Cu₃O_7?δ shifts to 588 cm^?1.     

Diode-laser-array end-pumped 1W CW Nd:YVO4/BIBO green laser

Abstract

This paper discusses a diode-laser-array end-pumped Nd:YVO₄/BIBO green laser. Using a three-mirror folded cavity (V-shaped), a 1.06 W CW green output was obtained at an incident pump power of 8.5 W; the corresponding optical conversion efficiency was 12.5%. The relationship between the green output and the temperature of the BIBO crystal was investigated. The laser damage threshold of BIBO crystal was measured to be 600 MW cm^?2 and 400 MW cm^?2 at 1064 nm and 532 nm, respectively.     

Thin polycrystalline zinc oxide films obtained by oxidation of metallic zinc films

Thin polycrystalline ZnO films were obtained by thermal oxidation of metallic Zn films, thermally deposited on various substrates, such as silica, sapphire and glass, in both air and pure oxygen atmospheres. The quality of the ZnO layers was asserted by Hall effect, cathodoluminescence and atomic force microscopy measurements. Electron concentration of 7.32×10¹² cm⁻³ and mobility of 14.2 cm²/V s with root mean square roughness of 30 nm were obtained for the 900 °C annealed ZnO films in oxygen. Room temperature cathodoluminescence spectra consisted of a narrow near band edge luminescence band and a broad defect-related green band with peak positions at 380 and 500 nm, respectively. ZnO film luminescence properties improved dramatically with the increase of annealing temperature and decrease of O₂ pressure.     

Microstructure and optical characterization of nanometric silicon films prepared by pulsed laser ablation

The effect of laser energy density, during pulsed laser ablation, on the microstructure and optical properties of silicon films has been investigated using techniques such as atomic force microscopy, scanning electron microscopy, X-ray diffraction, and UV–visible absorption/transmission spectroscopy. The thickness of prepared films increases with increase in laser energy density. The crystallite size and hence the crystallinity of prepared films have been estimated by X-ray diffraction and found to be dependent on laser energy density. The transmittance of films changes with laser energy density. The absorption coefficient of films has been found to be?>10⁴?cm^?1 in wavelength region 450–1100?nm. The band gap of silicon films has been determined as 2.27, 2.11, and 1.90?eV corresponding to laser energy density of 1.5, 2.5, and 3.5?J?cm^?2, respectively.     

Two-photon pumped upconversion and nonlinear optical properties of a new lasing dye: HMASPS

Abstract

Two-photon pumped frequency upconversion optical properties and two-photon absorption (TPA) induced nonlinear absorption of a new dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium ptoluene sulfonate (abbreviated to HMASPS) have been experimentally investigated. This new dye exhibits strong superradiation properties when the pumping power is above its threshold. The superradiation upconversion efficiency from 900 to 1150 nm and the nonlinear absorption from 720 to 1100 nm have been measured. The largest effective molecular TPA cross-section was measured to be 44.3 × 10^?48 cm⁴·s·photon^?1at 920 nm. At 1064 nm, it was 2.77 × 10^?48 cm⁴·s·photon^?1, much smaller than that at 920 nm. The highest conversion efficiency is 7% at 990 nm, whereas 4.2% at 1064 nm.     

Comparative studies on structural, optoelectronic and electrical properties of SILAR grown PbS thin films from acidic, neutral and alkaline cationic reaction bath

Thin films of Lead sulphide (PbS) were grown on soda lime glass substrate by Successive Ionic Layer Adsorption and Reaction method from acidic, neutral and alkaline cationic precursor reaction bath by keeping the pH of the anionic precursor invariant. The structural and morphological aspects of the as prepared samples were investigated using XRD and SEM results. The as-prepared samples were polycrystalline with nanometer sized grains and identified as galena type cubic structure. The values of average crystallite size were found to be in the range 22–30?nm. The SEM micrographs show variations in morphology. Optical studies revealed the existence of both direct and indirect band gap with values in the range of 1.65–1.98 and 0.61–0.90?eV respectively. The room temperature conductivity of the PbS thin films were in the range 1.19?×?10^?8–5.92?×?10^?8?Ω?cm^?1. The optical band gap energy has inverse relation with grain size and electrical conductivity is closely related to structural parameters like grain size, crystallinity and micro strain. The estimated lattice parameter, grain size, optical band gaps, solid state and electrical properties were correlated with pH of the cationic solution. In this work, we establish that the pH of the cationic precursor media has colossal effect on the structural, morphological, optoelectronic, solid-state and electrical properties of PbS thin films.     

Nanocrystalline CuO thin films: synthesis, microstructural and optoelectronic properties

Nanocrystalline copper oxide (CuO) thin films have been synthesized by a sol–gel method using cupric acetate Cu (CH₃COO) as a precursor. The as prepared powder was sintered at various temperatures in the range of (300–700?°C) and has been deposited onto a glass substrates using spin coating technique. The structural, compositional, morphological, electrical optical and gas sensing properties of CuO thin films have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Four Probe Resistivity measurement and UV–visible spectrophotometer. The variation in annealing temperature affected the film morphology and optoelectronic properties. X-ray diffraction patterns of CuO films show that all the films are nanocrystallized in the monoclinic structure and present a random orientation. The crystallite size increases with increasing annealing temperature (40–45?nm).The room temperature dc electrical conductivity was increased from 10^?6 to 10^?5 (Ω?cm)^?1, after annealing due to the removal of H₂O vapor which may resist conduction between CuO grain. The thermopower measurement shows that CuO films were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure. The electron carrier concentration (n) and mobility (μ) of CuO films annealed at 400–700?°C were estimated to be of the order of 4.6–7.2?×?10¹⁹?cm^?3 and 3.7–5.4?×?10^?5?cm²?V^?1?s^?1?respectively. It is observed that CuO thin film annealing at 700?°C after deposition provide a smooth and flat texture suited for optoelectronic applications. The optical band gap energy decreases (1.64–1.46?eV) with increasing annealing temperature. It was observed that the crystallite size increases with increasing annealing temperature. These modifications influence the morphology, electrical and optical properties.     

Direct Measurements of the Strong Refractive Nonlinearity of Impurity Origin in Heavily-doped GaAs

Abstract

A strong dispersive nonlinearity below the band gap in heavily doped bulk n-GaAs is observed for differnet donor impurities. Negative refractive index changes of up to ?5 × 10^?3 are obtained in the spectral range 880–900 nm, induced by light of the same wavelength at an incident intensity of about 5 × 10⁵ W cm^?2. Since the lifetime of the nonlinearity is ～ 10^?10 s, it is suggested that a bistable device exploiting this effect could be constructed with a switching energy of (1?5) × 10^?14 J μm^?2.     

Carrier properties of B atomic-layer-doped Si films grown by ECR Ar plasma-enhanced CVD without substrate heating

Abstract

The atomic-layer (AL) doping technique in epitaxy has attracted attention as a low-resistive ultrathin semiconductor film as well as a two-dimensional (2-D) carrier transport system. In this paper, we report carrier properties for B AL-doped Si films with suppressed thermal diffusion. B AL-doped Si films were formed on Si(100) by B AL formation followed by Si cap layer deposition in low-energy Ar plasma-enhanced chemical-vapor deposition without substrate heating. After fabrication of Hall-effect devices with the B AL-doped Si films on unstrained and 0.8%-tensile-strained Si(100)-on-insulator substrates (maximum process temperature 350°C), carrier properties were electrically measured at room temperature. Typically for the initial B amount of 2?×?10¹⁴ cm^?2 and 7?×?10¹⁴ cm^?2, B concentration depth profiles showed a clear decay slope as steep as 1.3 nm/decade. Dominant carrier was a hole and the maximum sheet carrier densities as high as 4?×?10¹³ cm^?2 and 2?×?10¹³ cm^?2 (electrical activity ratio of about 7% and 3.5%) were measured respectively for the unstrained and 0.8%-tensile-strained Si with Hall mobility around 10–13 cm² V^?1 s^?1. Moreover, mobility degradation was not observed even when sheet carrier density was increased by heat treatment at 500–700 °C. There is a possibility that the local carrier (ionized B atom) concentration around the B AL in Si reaches around 10²¹ cm^?3 and 2-D impurity-band formation with strong Coulomb interaction is expected. The behavior of carrier properties for heat treatment at 500–700 °C implies that thermal diffusion causes broadening of the B AL in Si and decrease of local B concentration.     

Ionic liquid-assisted hydrothermal synthesis of TiO2 nanoparticles and its application in photocatalysis

Anatase TiO₂ nanoparticles have been successfully synthesized at 130 °C for 2 days via ionic liquid-assisted hydrothermal method. The obtained products are characterized using various techniques. The X-ray diffraction data reveal that the nanoparticles are anatase TiO₂. FTIR spectrum shows that the presence of ionic liquid and indicates Ti–O–Ti peak at around 398 cm^?1, and the bands at 1500 and 1600 cm^?1 indicates C–H in-plane vibrations and stretching of imidazolium ring. Raman spectroscopy show bands at 142, 393, 513, and 636 cm^?1 reveal crystalline anatase phase. UV–Vis spectroscopy shows the λ _max at 355 nm corresponding to a band gap of 3.49 eV. TEM images reveal that the average diameters of anatase TiO₂ nanoparticles are in the range 50–100 nm. Anatase TiO₂ exhibited excellent photocatalysis for the degradation of organic dye.     

Hydrothermal synthesis and effects of pH values on properties of CdWO4 powders

Cadmium tungstate (CdWO₄) powders were synthesized by a hydrothermal method at different pH values. The samples show a pure monoclinic phase with the wolframite structure when they are synthesized at higher pH values. And the sample shows the highest crystallinity at a pH value of 7. All of the CdWO₄ samples show the characteristic band at 788 cm^?1 corresponding to symmetrical stretching vibration of W–O–W bond in WO₄ ^2? group in Fourier transform infrared absorption spectra. The transmission electron microscope results show that the particle sizes increase with the increase of pH value, according with the results of X-ray diffraction. All synthesized CdWO₄ samples show a broad blue–green emission at 350–550 nm. The emission intensity of sample synthesized at a pH value of 4 is nearly five times of that synthesized at a pH value of 1. These results indicate that the pH values have obvious influence on properties of CdWO₄ crystal in the hydrothermal synthesis.     

Optical absorption and electron spin resonance studies of Cu2+ in Li2O-Na2O-B2O3-As2O3 glasses

The local structure around Cu²⁺ ion has been examined by means of electron spin resonance and optical absorption measurements in xLi₂O-(40-x)Na₂O-50B₂O₃-10As₂O₃ glasses. The site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The ground state of Cu²⁺ isd _x ²−y ².The glass exhibited broad absorption band near infrared region and small absorption band around 548 nm, which was assigned to the ²B_1g →²E_g transition.     

Functionalized Graphene Quantum Dot Modification of Yolk–Shell NiO Microspheres for Superior Lithium Storage

Yolk–shell NiO microspheres are modified by two types of functionalized graphene quantum dots (denoted as NiO/GQDs) via a facile solvothermal treatment. The modification of GQDs on the surface of NiO greatly boosts the stability of the NiO/GQD electrode during long‐term cycling. Specifically, the NiO with carboxyl‐functionalized GQDs (NiO/GQDs? COOH) exhibits better performances than NiO with amino‐functionalized GQDs (NiO/GQDs? NH₂). It delivers a capacity of ≈1081 mAh g^?1 (NiO contribution: ≈1182 mAh g^?1) after 250 cycles at 0.1 A g^?1. In comparison, NiO/GQDs? NH₂ electrode holds ≈834 mAh g^?1 of capacity, while the bald NiO exhibits an obvious decline in capacity with ≈396 mAh g^?1 retained after cycling. Except for the yolk–shell and mesoporous merits, the superior performances of the NiO/GQD electrode are mainly ascribed to the assistance of GQDs. The GQD modification can support as a buffer alleviating the volume change, improve the electronic conductivity, and act as a reservoir for electrolytes to facilitate the transportation of Li⁺. Moreover, the enrichment of carboxyl/amino groups on GQDs can further donate more active sites for the diffusion of Li⁺ and facilitate the electrochemical redox kinetics of the electrode, thus together leading to the superior lithium storage performance.     

Enhancing Performance of Nonfullerene Acceptors via Side‐Chain Conjugation Strategy

A side‐chain conjugation strategy in the design of nonfullerene electron acceptors is proposed, with the design and synthesis of a side‐chain‐conjugated acceptor (ITIC2) based on a 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b :4,5‐b′ ]di(cyclopenta‐dithiophene) electron‐donating core and 1,1‐dicyanomethylene‐3‐indanone electron‐withdrawing end groups. ITIC2 with the conjugated side chains exhibits an absorption peak at 714 nm, which redshifts 12 nm relative to ITIC1. The absorption extinction coefficient of ITIC2 is 2.7 × 10⁵m ^?1 cm^?1, higher than that of ITIC1 (1.5 × 10⁵m ^?1 cm^?1). ITIC2 exhibits slightly higher highest occupied molecular orbital (HOMO) (?5.43 eV) and lowest unoccupied molecular orbital (LUMO) (?3.80 eV) energy levels relative to ITIC1 (HOMO: ?5.48 eV; LUMO: ?3.84 eV), and higher electron mobility (1.3 × 10^?3 cm² V^?1 s^?1) than that of ITIC1 (9.6 × 10^?4 cm² V^?1 s^?1). The power conversion efficiency of ITIC2‐based organic solar cells is 11.0%, much higher than that of ITIC1‐based control devices (8.54%). Our results demonstrate that side‐chain conjugation can tune energy levels, enhance absorption, and electron mobility, and finally enhance photovoltaic performance of nonfullerene acceptors.     

Characterization of various Eu2+ sites in Ca2SiO4:Eu2+ and Ba2SiO4:Eu2+ by high-pressure spectroscopy

Photoluminescence of Ba₂SiO₄ and Ca₂SiO₄ activated with Eu²⁺ was investigated at various temperatures (from 10 K to 300 K) and pressures (from ambient to 200 kbar). At ambient pressure and room temperature, under UV excitation both phosphors yielded a green emission band with maxima at 505 nm and 510 nm for Ba₂SiO₄ and Ca₂SiO₄, respectively. The energies of these bands depended on pressure; the pressure shifts were ?12:55 cm^?1/kbar for Ba₂SiO₄:Eu²⁺; and ?5:59 cm^?1/kbar for Ca₂SiO₄:Eu²⁺. In the case of Ca₂SiO₄:Eu²⁺, we observed additional broadband emission at lower energies with a maximum at 610 nm (orange band). The orange and green emission in Ca₂SiO₄:Eu²⁺ had different excitation spectra: the green band could be excited at wavelengths shorter than 470 nm, whereas the orange band — at wavelengths shorter than 520 nm. The pressure caused a red shift of orange emission of 7.83 cm^?1/kbar. The emission peaked at 510 nm was attributed to the 4f⁶5d→4f⁷(⁸S₇₌₂) transition of Eu²⁺ in the β — Ca₂SiO₄:Eu²⁺ phase, whereas the emission peaked at 610 nm — to the γ — Ca₂SiO₄:Eu²⁺ phase. The emission of Ba₂SiO₄:Eu²⁺ peaked at 505 nm was attributed to the 4f⁶5d→ 4f⁷(⁸S_7/2) transition of Eu²⁺ in the β — Ba₂SiO₄ phase.     

Atomic carbon in magnesium oxide Part VII: Infrared analysis of OH-containing defects

The multitude of OH stretching bands in the near IR in arc-fused MgO can be divided into two main groups, a triangular shaped band at 3548 cm^?1 (300K) which strongly shifts and splits to a triplet at 3571, 3566 and 3550 cm^?1 upon cooling to 82 K, a quadruplet at 3297, 3312, 3327 and 3342 cm^?1 (82 K), plus a broad background absorption extending from 3600 – 3300 cm^?1. The H-H band at 4150 cm^?1 points at molecular H formed by charge transfer from [OH^· V″_Ma HO^·]^x = [O^· (H₂)″_Mg O^·]^x. The broad background absorption is assigned to interstitial protons, H^·₁. The 3300 and 3550 cm^?1 groups are assigned to the diamagnetic defects [OH^· V″_Ma]¹ and [OH^· V″_Mg HO^·]^x respectively. Their multiplet structure is explained by interaction of the OH oscillator with near-by C^x₁ atoms on interstitial sites surrounded by an elastic strain halo which causes local lattice expansion.     

Investigation of optical damage in the nonlinear optical crystal (−)2-(α-methylbenzylamino)-5-nitropyridine

Abstract

Pulsed laser induced surface damage experiments were made on the cleaved (001) face of (—)2-(α-methylbenzylamino)-5-nitropyridine (MBANP) crystals using a pulse length of 25 ns FWHM. The highest single pulse damage threshold value was 24·2 J cm^?2 at a wavelength of 1064 nm for light polarized along the crystallographic a axis, whereas the lowest was 1·8 J cm^?2 at 532 nm for light polarized along the crystallographic b axis. The extent of the mechanical distortion of the (001) crystal plane consequent upon the absorption of a 25 ns FWHM, 10 J cm^?2 pulse from a Nd:YAG laser operating at the wavelength 1064 nm has been measured by a non-destructive and non-invasive technique.     

Photoluminescence and thermoluminescence studies of Tb3+ doped ZnO nanorods

Here in, the synthesis of the terbium doped zinc oxide (ZnO:Tb³⁺) nanorods via room temperature chemical co-precipitation was explored and their structural, photoluminescence (PL) and thermoluminescence (TL) studies were investigated in detail. The present samples were found to have pure hexagonal wurtzite crystal structure. The as obtained samples were broadly composed of nanoflakes while the highly crystalline nanorods have been formed due to low temperature annealing of the as synthesized samples. The diameters of the nanoflakes are found to be in the range 50–60 nm whereas the nanorods have diameter 60–90 nm and length 700–900 nm. FTIR study shows ZnO stretching band at 475 cm^?1 showing improved crystal quality with annealing. The bands at 1545 and 1431 cm^?1 are attributed to asymmetric and symmetric CO stretching vibration modes. The diffuse reflectance spectra show band edge emission near 390 nm and a blue shift of the absorption edge with higher concentration of Tb doping. The PL spectra of the Tb³⁺-doped sample exhibited bright bluish green and green emissions at 490 nm (⁵D₄ → ⁷F₆) and 544 nm (⁵D₄ → ⁷F₅) respectively which is much more intense then the blue (450 nm), bluish green (472 nm) and broad green emission (532 nm) for the undoped sample. An efficient energy transfer process from ZnO host to Tb³⁺ is observed in PL emission and excitation spectra of Tb³⁺-doped ZnO ions. The doped sample exhibits a strong TL glow peak at 255 °C compared to the prominent glow peak at 190 °C for the undoped sample. The higher temperature peaks are found to obey first order kinetics whereas the lower temperature peaks obey 2nd order kinetics. The glow peak at 255 °C for the Tb³⁺ doped sample has an activation energy 0.98 eV and frequency factor 2.77 × 10⁸ s^?1.     

Hydrothermal synthesis and photoluminescence properties of cerium-doped cadmium tungstate nanophosphor

The present paper reports synthesis and photoluminescence studies of cadmium tungstate (CdWO₄) and cerium-doped cadmium tungstate. The samples were synthesised by low cost and low temperature hydrothermal method and characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and photoluminescence analysis. XRD pattern reveals that the CdWO₄ has monoclinic wolframite structure. The FTIR spectrum of cerium-doped CdWO₄ exhibits broadband below 700 cm^?1 which is due to the δ (Ce–O–C) mode. The TEM images show that size of particle is approximately 60–120 nm in both samples. A broad intense peak was observed at 474 nm when the samples were excited with 263 nm. A broad intense peak was observed at 475 nm when the samples were excited with 600 nm. The intensity of the 474 nm peak decreases with increase in cerium doping concentration. The observation of 475 nm peak when excited with 600 nm is upconversion luminescence. This upconversion emission is due to energy transfer upconversion process involving Cd²⁺ ions and [WO₆]^6? ions. Ce³⁺ ion is responsible for the peak shift of 6 nm.