Bi2O3纳米晶玻璃三阶非线性光吸收性质的研究

利用溶胶凝胶法结合气氛控制方式合成了含Bi2O3纳米晶钠硼硅玻璃.利用X射线粉末衍射仪(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、X射线能量色散谱(EDX)、扫描模式透射电子显微镜(STEM)、高分辨透射电子显微镜(HRTEM)以及选区电子衍射(SAED)对掺杂在钠硼硅玻璃中Bi2O3纳米晶的形貌和微结构进行了表征,同时,利用飞秒开孔Z-scan技术详细地研究了Bi2O3纳米晶玻璃在800 nm处不同激发光强度下的三阶非线性光吸收性质.结果表明,在钠硼硅玻璃中形成了尺寸小于10 nm的Bi2O3单斜晶系纳米晶.随着激发光强度的增强,该玻璃的三阶非线性光吸收性质产生由饱和吸收向反饱和吸收的转变.进一步,计算得到的该玻璃三阶非线性极化率χ(3)的数量级范围在10-19~10-18m2/V2之间.这一结果说明该玻璃具有良好的非线性光学性能,并且在光限幅器等非线性光学领域具有潜在的应用价值.     

Microstructures and the third-order optical nonlinearities of semimetal Bi nanocrystals in the sodium borosilicate glass

The sodium borosilicate glass doped with semimetal Bi nanocrystals is prepared by employing both sol-gel and atmosphere control methods. Microstructures and the third-order optical nonlinearities of the glass are investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and Z-scan technique. The results show that semimetal Bi nanocrystals in hexagonal crystal system with spherical shape have formed uniformly in the glass, and the size of these nanocrystals is almost less than 40 nm. Furthermore, the third-order optical nonlinear refracitve index γ, absorption coefficient β, and susceptibility χ⁽³⁾ of the glass are determined to be 9.40 × 10⁻¹⁷ m²/W, 1.25 × 10⁻⁹ m/W, and 6.80 × 10⁻¹¹ esu, respectively.     

Third-order nonlinear optical properties of Bi2S3 nanocrystals doped in sodium borosilicate glass studied with Z-scan technique

The third-order nonlinear optical properties of Bi₂S₃ nanocrystals doped in sodium borosilicate glass are measured by Z-scan technique. The microstructures of the glass are characterized by means of X-ray diffraction, transmission electron microscopy, scanning transmission electron microscopy, energy dispersion X-ray spectra, and high-resolution transmission electron microscopy. The results show that the Bi₂S₃ nanocrystals ranging from 10 to 30 nm are determined to be of the orthorhombic crystalline phase, and the third-order optical nonlinear refractive index γ, absorption coefficient β, and susceptibility χ⁽³⁾ of the glass are determined to be 2.56 × 10⁻¹⁶ m² W⁻¹, 4.13 × 10⁻¹⁰ mW⁻¹, and 1.43 × 10⁻¹⁰ esu, respectively.     

Bi2S3纳米晶掺杂钠硼硅玻璃的三阶非线性光学性质

利用溶胶-凝胶方法制备了1 wt%Bi2S3纳米晶掺杂钠硼硅玻璃.利用X射线粉末衍射仪(XRD),X射线光电子能谱(XPS),透射电子显微镜(TEM),X射线能量色散谱(EDX),扫描模式透射电子显微镜(STEM)以及高分辨透射电子显微镜(HRTEM)对Bi2S3纳米晶在钠硼硅玻璃中的形貌和微结构进行了表征,同时,利用飞秒Z扫描技术在波长为770 nm对该玻璃的三阶非线性光学性能进行了分析测试.结果表明,尺寸为10～30 nm的Bi2S3正交晶系纳米晶在钠硼硅玻璃中形成,该玻璃的三阶非线性光学折射率γ、三阶非线性吸收率β和三阶非线性极化率χ(3)分别为5.90×10-16 m2/W、7.35×10-9 m/W和4.55×10-18 m2/V2.其中,该玻璃的三阶非线性极化率值比未经掺杂的钠硼硅玻璃(χ(3)=1.09×10-22 m2/V2)高出4个数量级,这表明,随着Bi2S3纳米晶的引入,该玻璃的三阶非线性光学性能将得到显著的提高.     

Sub-2 nm SnO2 nanocrystals: A reduction/oxidation chemical reaction synthesis and optical properties

A simple reduction/oxidation chemical solution approach at room temperature has been developed to synthesize ultrafine SnO₂ nanocrystals, in which NaBH₄ is used as a reducing agent instead of mineralizers such as sodium hydroxide, ammonia, and alcohol. The morphology, structure, and optical property of the ultrafine SnO₂ nanocrystals have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy. It is indicated that the uniform tetragonal ultrafine SnO₂ nanocrystals with the size below 2 nm have been fabricated at room temperature. The band gap of the ultrafine SnO₂ nanocrystals is about 4.1 eV, exhibiting 0.5 eV blue shift from that of the bulk SnO₂ (3.6 eV). Furthermore, the mechanism for the reduction/oxidation chemical reaction synthesis of the ultrafine SnO₂ nanocrystals has been preliminary presented.     

Preparation and optical study of CdS nanocrystals embedded phosphate glass

A new phosphate glass system with CdS nanocrystals dispersed in glass matrix was investigated. The phosphate glass composition with good stability has been used for preparation of CdS doped glasses. The CdS in the range of 0.5-7.0% has been doped into this glass composition. Effect of CdS content on the optical and other properties has been investigated. The optical characterization of the glass samples showed that with increasing concentration of CdS, there was a red shift in transmission cut-off of the glasses. From the transmission cut-off of each glass sample, the band gap of the CdS nanocrystals embedded glass was calculated. The band gap of CdS particles embedded glass was observed in the range of 3.1-4.1 eV. The present system is compared with CdS nanocrystals doped in silica based glass system. In the phosphate glass system, the UV transmission cut-off's are not sharp and the optical transmittance decreases with increasing CdS content in contrast to silica glass system. The reason for such behavior has been discussed in the present investigation. TEM of the CdS doped phosphate glasses showed CdS particle size in the range of 5-7 nm for lower concentration of CdS and 10-100 nm for higher concentration of CdS. The nanocrystals are non-uniform in size but uniformly dispersed in glass matrix.     

Structure and luminescence properties of Eu/Tb codoped oxyfluoride glass ceramics containing Sr2GdF7 nanocrystals

Eu/Tb codoped transparent oxyfluoride borosilicate glass ceramics containing Sr₂GdF₇ nanocrystals were fabricated under a reductive atmosphere and the conversion of Eu³⁺ ions to Eu²⁺ ions was observed. The Sr₂GdF₇ nanocrystals with an average size of 32 nm were homogeneously precipitated in the oxyfluoride borosilicate glass matrix, which could be evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy. The enhancement of photoluminescence emission intensity, reduction of the relative emission intensities between ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁, and long fluorescence lifetimes of Eu²⁺, Eu³⁺, and Tb³⁺ ions revealed that more rare earth ions were partitioned into the low phonon energy environment Sr₂GdF₇ nanocrystals. Under ultraviolet excitation, pure and bright white light emission was obtained in the oxyfluoride borosilicate glass ceramic, which may be a potential blue, green and red-emitting phosphor for white LEDs.     

Microstructure and optical absorption property of the Cu/SiO2 nano-films

Cu/SiO₂ nano-composite thin films were prepared by a sol–gel method. The structure and optical property of the films were investigated with a special emphasis on the influences of Cu content. Cu particles were basically spherical and dispersed in the SiO₂ matrix. The optical absorption peaks due to the surface plasmon resonance of Cu particles were observed in the wavelength range of 550–600 nm. The absorption property is enhanced with increasing Cu content, showing a maximum value in the films with 30 at.% Cu. Increasing Cu content above 30 at.% results in a decrease in absorption intensity. The absorption peak shows a red-shift trend with increasing Cu content from 5 to 30 at.% and then turns to blue-shift by further increasing the Cu content from 30 to 35 at.%. The band gap Eg decreases with increasing Cu content from 10 to 30 at.% but increases by further increasing Cu content.     

Electrical and gas sensing properties of self-aligned copper-doped zinc oxide nanoparticles

Electrical and gas sensing properties of nanocrystalline ZnO:Cu, having Cu X wt% (X = 0.0, 0.5, 1.0, and 1.5) in ZnO, in the form of pellet were investigated. Copper chloride and zinc acetate were used as precursors along with oxalic acid as a precipitating reagent in methanol. Material characterization was done by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM) and inductive coupled plasma with optical emission spectrometry (ICP-OES). FE-SEM showed the self-aligned Cu-doped ZnO nano-clusters with particles in the range of 40-45 nm. The doping of 0.5% of copper changes the electrical conductivity by an order of magnitude whereas the temperature coefficient of resistance (TCR) reduces with increase in copper wt% in ZnO. The material has shown an excellent sensitivity for the H₂, LPG and CO gases with limited temperature selectivity through the optimized operating temperature of 130, 190 and 220 °C for H₂, LPG and CO gases, respectively at 625 ppm gas concentration. The %SF was observed to be 1460 for H₂ at 1% Cu doping whereas the 0.5% Cu doping offered %SF of 950 and 520 for CO and LPG, respectively. The response and recovery time was found to be 6 to 8 s and 16 s, respectively.     

Characterisation of size-controlled and red luminescent Ge nanocrystals in multilayered superlattice structure

Ge nanocrystals (Ge NCs) embedded in a multilayered superlattice structure have been fabricated and investigated. The presence of Ge NCs was confirmed by Raman scattering and X-ray diffraction measurements. The average size of Ge NCs was modulated by the sputtering time of Ge-rich layer and possible mechanisms have been proposed. The blue shift of optical absorption edge was observed with the decrease of nanocrystal size. The photoluminescence showed broad bands centred at ∼ 1.77 eV and ∼ 2.01 eV for 3.9 nm and 3.0 nm nanocrystals, respectively, which are consistent with the theoretical calculation in literature. The properties of shifted optical absorption and red luminescence are tentatively explained by quantum confinement in the Ge NCs.     

Porphyrin based hybrid borate glasses: Structure and photophysical investigation

Freebase tetra phenyl porphyrin (H₂TPP) and its derivatives in different concentration ranges (0.5–2.0 mg per 12 g of boric acid) were incorporated into borate glass matrix by melt quenching technique at 230 °C. The formed glasses were stable and in green colour. The optical absorption and emission properties are different from that observed in solutions. The absorption spectrum shows a two line pattern Soret band at 435–454 nm and Q-band at 665–701 nm. The emission spectrum shows strong S₂ → S₀ emission at 490–520 nm region and S₁ → S₀ emission at 725–810 nm. The time resolved fluorescence decay of S₁ → S₀ emission shows three exponential decay. For example, in the case of 2 mg of H₂THP doped glass the lifetimes were found to be τ₁ = 0.511 ns (26.7%), τ₂ = 10 ps (64.68%) and τ₃ = 3.965 ns (8.62%). These unusual photophysical properties were found to arise from different structural motifs of porphyrin in the glass. These structures were further modeled through reactions of porphyrin with BF₃O(C₂H₅) in solution and DFT calculations.     

Formation of Si nanocrystals in glass by femtosecond laser micromachining

We report on the precipitation of Si nanocrystals inside a borosilicate glass by using an 800 nm, 250 kHz femtosecond laser irradiation, which was confirmed with X-ray diffraction, Raman spectra and transmission electron microscopy analyses. Refractive index profile reveals that the refractive index of the Si nanocrystals precipitated region increased up to 8.7% in comparison with that of the unirradiated area, leading to a large diffraction efficiency of the fabricated dot structure. Furthermore, the third-order optical nonlinearity of the Si nanocrystals precipitated glass is greatly enhanced based on the Z-scan measurement. These results may find applications for the fabrication diffractive optical devices and optical switches.     

Effect of Fe on the sintering and thermal properties of Mo–Cu composites

Effects of Fe on the sintering and thermal properties of Mo–Cu composites have been investigated. Mo–Cu–xFe composites are fabricated by powder metallurgy techniques with addition of various Fe contents ranging from 0.4 wt% to 2.2 wt%. The thermal properties and action mechanism of Fe to Mo–Cu composites are discussed. Results have indicated that the coefficient of thermal expansion (CTE) and thermal conductivity (TC) of Mo–Cu composites are greatly affected by the addition of Fe contents. It has also been observed that the fabricated composite powders with Fe additions exhibit high sinterability. Also, the inclusion of Fe can active the sintering course in shorter times and decline the sintering temperature thus also improving the physical properties of composites. Furthermore, it is also concluded that the utilization of steel kettle and steel balls for milling the Mo–Cu powders is also beneficial to improve the physical and thermal properties of Mo–Cu alloy.     

Size dependent structural, optical and morphological properties of ZnS:Cu thin films

ZnS:Cu thin films have been deposited on glass substrate by a simple neutral pH solution synthesis route and chemical bath deposition technique. The copper concentration was varied between 0 and 0.1 M%. The X-ray diffraction and scanning electron microscope studies show the average size of the nanoparticles are below 4 nm (Bohr diameter). The effect of film thickness on the optical and structural properties has been studied. The optical absorption studies show the band gap energy of ZnS:Cu films decreases from 3.68 to 3.43 eV as thickness varied from 318.3 to 334.1 nm. The structural estimation shows the variation in particle size from 2.67 to 3.14 nm with thickness. The insignificant change in band gap may be due to the increase in particle size and quantum size effect.     

Preparation and optical properties of borate glass doped with MnO<Subscript>2</Subscript>

In this contribution, MnO₂ doped borate glass matrix with ratios 0.0, 0.5, 1.0, 1.5 and 2.0 wt% were prepared utilizing melting method. The structural characterization of these glass samples was performed via X- ray diffraction measurements. Optical absorption analyses within the 200–1000 nm wavelength range were performed to characterize the samples. The direct and indirect optical energy gaps (E_opt) decreased however Urbach energy (E_U) increased with increasing MnO₂ concentration. The refractive index, and optical conductivity values are observed to increase with increasing MnO₂ concentration. FTIR spectra of borate glass doped with 0.0, 0.5, 1.0, 1.5 and 2.0 wt% MnO₂ revealed the presence of absorption bands due to Mn²⁺.     

Thermal annealing effect on the structure, bandgap, and optical constants of Er-Mn oxide thin films

Thin films of erbium-manganese oxide were grown on glass and p-type Si substrates. The films were thermally pre-annealed at different temperatures ranging from 400 to 1000 °C to produce different crystalline structures and agitate a solid-state reaction. The structural characterisation of the films was carried out by X-ray diffraction (XRD) and energy dispersion X-ray fluorescence (XRF). The XRD investigation shows that the films annealed at 400 °C were amorphous and nanocrystals of ErMnO₃ appear under pre-annealing at about 800 °C or more. Mn oxide and Er oxide prevent each other from crystallising alone. The optical properties of the films pre-annealed at different temperatures were studied in the fundamental absorption region of the spectrum in wavelength range 230-800 nm. The spectral complex refractive index, complex optical dielectric constant, and optical bandgap were determined. A modified single-oscillator Forouhi-Bloomer (FB) technique, Wemple-Didomenico (WD) equation, Urbach's relation, Tauc et al. relation, and pointwise unconditioned minimisation approach (PUMA) were used in the analysing of the obtained spectral data.     

Transport properties of microwave sintered pure and glass added MgCuZn ferrites

A series of pure stoichiometric and 1 wt% lead borosilicate (PBS) glass added MgCuZn ferrite with the general formula Mg_0.5Cu_xZn_0.5−xFe₂O₄ with x = 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 were synthesized by microwave sintering technique. Single phase spinel structure is exhibited by the XRD patterns of these ferrites. DC and AC conductivity were investigated as a function of composition, temperature and frequency. DC conductivities were also estimated using the impedance spectroscopy analysis of Cole–Cole plots. The DC conductivities thus obtained are in good agreement with the experimental results. All the investigated samples exhibited two regions of conductivity one in the low temperature and the second in the high temperature region. It is observed that PBS glass added samples have lower conductivities than pure samples. Due to their lower conductivities and sintering temperatures the 1 wt% PBS glass added samples are suitable for multilayer chip inductor (MLCI) and high definition TV deflection yoke material application.     

Rigidity of diamond reinforced metals featuring high particle contents

Diamond/metal composites with diamond contents between 57 and 72 vol% have been produced by gas pressure assisted liquid metal infiltration using Ag–3 wt% Si and Al–2 wt% Cu as matrix. The experimental data cover a range of Young’s moduli from 300 to 425 GPa and 245 to 370 GPa for the Ag–3Si and the Al–2Cu-based composites, respectively. Experimental Young’s moduli are compared to the Mori–Tanaka mean field scheme (MTM), the generalized self-consistent scheme (GSCS), the bimodal hard sphere model (TBHS), and the differential effective medium scheme (DEM). At the lower end of volume fractions investigated, the predictions by the GSCS, the TBHS, and the DEM are very close to each other and to the experimental results while the MTM is clearly lower. With increasing volume fraction the differences between the models accentuate and the data up to 72 vol% of diamond are best described by the DEM.     

ZnO micro and nanocrystals with enhanced visible light absorption

In this paper, we investigate the effect of the particle size and morphology on the optical properties of ZnO. A series of ZnO micro and nanocrystals were synthesized by the hydrothermal processing of zinc acetate dihydrate and sodium hydroxide as the starting materials, and polyvinylpyrrolidone (PVP) as the polymer surfactant. The particle size and morphology were tailored by adjusting the reactant molar ratios [Zn²⁺]/[OH⁻], while the reaction temperature and the time remained unchanged. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM) have shown that the micro and nanocrystals have a high crystalline pure wurtzite-type hexagonal structure with nanosized crystallites. The size and morphology of the ZnO micro and nanocrystals were investigated by field emission scanning electron microscopy (FE-SEM), which showed a modification from micro-rods via hexagonal-faceted prismatic morphology to nanospheres, caused by simple adjustment of the reactant molar ratio [Zn²⁺]/[OH⁻] from 1:1 to 1:5. The optical properties of the ZnO micro and nanocrystals, as well as their dependence on the particle size and morphology were investigated by Raman and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS). The UV–vis spectra showed that the modification of the particle size and morphology from nanospheres to micro-rods resulted in increased absorption, and a slight red-shift of the absorption edge (0.06 eV). Besides, the band gap energy of the synthesized ZnO micro and nanocrystals showed the red shift (∼0.20 eV) compared to bulk ZnO. According to the results of a Raman spectroscopy, the enhanced visible light absorption of the ZnO micro and nanocrystals is related to two phenomena: (1) the existence of lattice defects (oxygen vacancies and zinc interstitials), and (2) the particle surface sensitization by PVP.     

Novel Ga-doped ZnO nanocrystal ink: Synthesis and characterization

Ga-doped ZnO (GZO) nanocrystals were synthesized via the hot-injection method for the first time. The characterizations of its structure, composition, morphology, and absorption properties were conducted by using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and UV-vis absorption spectroscopy. The results indicated that GZO nanocrystals were single phase polycrystalline within a range of 5―10 nm. Optical measurements illustrated that GZO nanocrystals have a tunable band gap from 3.35 to 3.81 eV, depending on the Ga doping level. GZO nanocrystals were dispersed in nonpolar solvents to form a nanocrystal ink which could remain stable after a month of storage. The GZO thin film was fabricated by spin coating the GZO nanocrystal ink and annealing in air. The electrical resistivity of the film was measured to be 7.5 × 10⁻² Ω cm. This method, which eliminated the requirement of high vacuum and high temperature, was a promising alternative for transparent conducting oxide (TCO) fabrication.