A facile hydrothermal route to synthesize novel PbI2 nanorods

We report the synthesis of PbI₂ nanorods by reacting lead acetate with elemental iodine at room temperature by virtue of a wet chemical method at mild reactions. The diameters of the obtained PbI₂ nanorods are about 54 nm. The present technique may open a new doorway to one-dimensional nanosized rods from the same kind of materials with irregular shape or large size. X-ray powder diffraction (XRD), Fourier transform infrared analysis (FTIR), ultraviolet–visible–near infrared analysis (UV–vis–NIR), photoluminescence measurements (PL) and scanning electron microscopy (SEM) were used to characterize PbI₂ nanorods. The as obtained products were analyzed by X-ray powder diffraction, which confirms the formation of solid PbI₂ nanorods. From the UV–vis–NIR studies the band gap of PbI₂ nanorod was estimated. The various functional groups present in the PbI₂ nanorods were identified by FTIR analysis. Intense photoluminescence was also observed with some spectral tuning possibly giving a range of emission photon energies approximately spanning from 2.1 to 3.5 eV.     

Solution route to SnO2 crystals with controllable morphology

SnO₂ crystals with various morphologies were prepared by a facile hydrothermal method in the simple solution systems of SnCl₂ and SnCl₄, respectively. This process was carried out under mild conditions and required no high-temperature heat treatment. The morphological evolution with the preparation conditions was investigated. Various self-assembled hierarchical structures including microspheres assembled with nanoparticles, oriented nanocones, and flower-like, cabbage-like structures consisting of single-crystalline nanosheets were obtained by varying the solvent and the introduction of polyethylene glycol. A possible mechanism for the formation of the spherical hierarchically structures assembled by cone-like nanocrystals was proposed.     

Impurity transitions in the photoluminescence spectra of SnO2

The photoluminescence of SnO₂, a semiconductor with direct, dipole-forbidden gap, is investigated as a function of the lattice temperature and the excitation intensity. The new emission lines observed could be partly interpreted as donor-acceptor-pair recombination and as band-acceptor transition.     

Raman spectroscopic and photoluminescence study of single-crystalline SnO2 nanowires

Single-crystalline SnO₂ nanowires with sizes of 4-14 nm in diameter and 100-500 nm in length were produced in a molten salt approach by using hydrothermal synthesized precursor. Structural characters of the nanowires were examined by X-ray diffraction and high-resolution electron transmission microscopy. Raman, photoluminescence and X-ray photoelectron spectra of the samples were examined under heat treatments. Three new Raman modes at 691, 514 and 358 cm⁻¹ were recorded and assigned. The former two are attributed to activation of original Raman-forbidden A_2uLO mode and the third is attributed to defects in small-sized nanowires. A strong photoluminescence is observed at about 600 nm, the temperature effects is examined and the origin of the PL process is discussed via X-ray photoelectron spectra.     

Synthesis and photoluminescence properties of SnO2/ZnO hierarchical nanostructures

SnO₂/ZnO hierarchical nanostructures were synthesized by a two-step carbon assisted thermal evaporation method. SnO₂ nanowires were synthesized in the first step and were then used as substrates for the following growth of ZnO nanowires in the second step. Sn metal droplets were formed at the surfaces of the SnO₂ nanowires during the second step and were acted as catalyst to facilitate the growth of ZnO nanowires via vapor-liquid-solid mechanism. Room temperature photoluminescence measurements showed that the SnO₂/ZnO hierarchical nanostructures exhibited a strong green emission centered at about 520 nm and a weak emission centered at about 380 nm. The emissions from the SnO₂ were drastically constrained due to screen effect caused by the ZnO layer.     

Growth mechanism and photoluminescence of the SnO2 nanotwists on thin film and the SnO2 short nanowires on nanorods

SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au-Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders.The morphology and the structure of the prepared nanostructures are determined on the basis of field-emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),selected area electronic diffraction(SAED),high-resolution transmission electron microscopy(HRTEM),x-ray diffraction(XRD),Raman and photoluminescence(PL) spectra analysis.The new peaks at 356,450,and 489 nm in the measured PL spectra of two kinds of SnO2 nanostructures are observed,implying that more luminescence centres exist in these SnO2 nanostructures due to nanocrystals and defects.The growth mechanism of these nanostructures belongs to the vapour-liquid-solid(VLS) mechanism.     

Excitation process and photoluminescence properties of Tb and Eu ions in SnO2 and in SnO2: Porous silicon hosts

Tin oxide (SnO₂)-layers-doped terbium and europium ions are elaborated by the sol-gel method on silicon substrates. After annealing at 500 °C, the transmission electron microscopy revealed a crystallization of tin oxide.The emission properties of rare-earth in SnO₂ are studied systematically against temperature annealing and Tb³⁺ concentration. The PL spectrum is optimal after annealing at 900 °C and the corresponding photoluminescence (PL) decay is nearly exponential, showing that the sample is homogenous and the PL process can be described by two levels system.The concentration effect shows a quenching of the PL intensity for Tb³⁺ concentration above 4%. From the investigation of the decay rate from the ⁷F₅ state within terbium concentration, we show that self-quenching is insured by dipole - dipole interaction. The evolutions of both PL intensity and PL lifetime versus temperature are studied. The PL intensity and PL lifetime are enhanced by deposing SnO₂:Tb³⁺ and SnO₂:Eu³⁺ in porous silicon. We show that an efficient excitation transfer from Si nanocrystallites to RE ions can occur.     

SnO2 / In2O3 one-dimensional nano-core-shell structures: Synthesis, characterization and photoluminescence properties

SnO₂/In₂O₃ one-dimensional nano-core-shell structures have been synthesized at 1350 ^°C by thermal evaporation of the mixture of metal Sn, Fe(NO₃)₃ powders and In particles. The as-synthesized products have been characterized by energy-dispersive X-ray spectroscopy, selected-area electron diffraction and high-resolution transmission electron microscopy. Microstructure characterization indicates the orientation relationship between core and shell is , . The formation mechanism of this nano-core-shell structure can be attributed to the cover of In₂O₃ on the surface of SnO₂ nanochains. The photoluminescence properties of the nano-core-shell structures have been measured. The PL spectrum shows some difference with the result from pure SnO₂ and In₂O₃ nanostructure that be deemed to relate to interface defects in SnO₂/In₂O₃ nano-core-shell structure.     

蓝宝石衬底SnO2:Sb薄膜的制备及结构和光致发光性质

用射频磁控溅射法在蓝宝石(0001)衬底上制备出锑掺杂的氧化锡(SnO₂:Sb)薄膜.对制备薄膜的结构和发光性质进行了研究.制备样品为多晶薄膜，具有纯SnO₂的四方金红石结构.室温条件下对样品进行光致发光测量，在334 nm附近观测到紫外发射峰，并对SnO₂:Sb的光致发光机制进行了研究.     

SnO2:Eu nanoparticles dispersed in silica: A low-temperature synthesis and photoluminescence study

SnO₂:Eu and SnO₂:Eu nanoparticles dispersed in silica matrix were prepared at a relatively low temperature of 185 °C in ethylene glycol medium. For as-prepared SnO₂:Eu nanoparticles there exists a weak energy transfer from the SnO₂ host to the Eu³⁺ ions. However, the energy transfer can be significantly improved by dispersing the Eu³⁺-doped SnO₂ nanoparticles in silica matrix. Effective shielding of surface Eu³⁺ ions in SnO₂:Eu nanoparticles from the stabilizing ligand by silica matrix is the reason for the improved extent of energy transfer. Increase in asymmetric ratio of luminescence (ratio of the intensity of the electric dipole allowed transition, ⁵D₀→⁷F₂, to magnetic dipole allowed transition, ⁵D₀→⁷F₁) for SnO₂:Eu nanoparticles dispersed in silica compared to that of SnO₂:Eu nanoparticles, has been attributed to the distorted environment around surface Eu³⁺ ions brought about by the presence of both tin and silicon structural units. ¹¹⁹Sn and ²⁹Si MAS NMR studies on this sample confirmed that there is no interaction between the tin and silicon structural units even after heating the samples at 900 °C.     

Temperature dependence of photoluminescence property in BaIn2O4

The temperature-dependent photoluminescence(PL) spectra of BaIn2O4,prepared by coprecipitation,are measured and discussed.Aside from the reported 3.02-eV violet emission,the 1.81-eV yellow emission involved with oxygen vacancy is also observed at room temperature wherein the deep donor level is at 1.2 eV.With the temperature increasing,the peak energies for both emissions show a red shift.Moreover,the yellow emission intensity decreases while the violet emission intensity increases.The temperature dependence of the yellow emission intensity fits very well into the one-step quenching process equation,indicating a fitted activation energy at 19.2 meV.     

六角星形MoSe_2双层纳米片的制备及其光致发光性能

采用化学气相沉积法,以三氧化钼作为钼源,硒粉作为硒源,在H_2/Ar气氛下生长出硒化钼纳米片.扫描电镜、X射线衍射表征结果表明,MoSe_2产物呈六角星状,横向尺寸约10μm,具有很好的晶体质量和结构.拉曼光谱表征其结构,确定其为双层纳米片.研究表明,高温反应时间对双层纳米片的生长具有重要的影响.通过对双层纳米片的生长机理的探究,推测其经历了3个生长过程:在高温下,Mo源和Se源被气化成气态分子并发生硒化反应形成晶核;晶核呈三角形外延生长;当反应时间持续增加,在空间位阻效应的影响下,晶体以中心原子岛为核,外延耦合生长出第二层三角形,最终形成六角星状双层纳米片.光致发光光谱结果表明,六角星状MoSe_2双层纳米片在1.53 eV处具有直接带隙和1.78 eV处具有间接带隙,其较宽范围的激发光谱响应预测其在光电探测器件领域具有潜在的应用前景.     

Structure, microstructure and photoluminescence properties of Fe doped SnO2 thin films

In this paper, effects of Fe doping on crystallinity, microstructure and photoluminescence (PL) properties of sol-gel derived SnO₂ thin films are reported. It is shown that doping of Fe³⁺ ions leads to crystallite size reduction and higher strain in SnO₂ thin films. The room temperature PL spectra show marked changes in intensity and blue-shift of the emission lines upon Fe doping. These observations have been correlated with structural changes and defect chemistry of Fe doped SnO₂ thin films.     

合成温度和N2/O2流量比对碳纤维衬底上生长的SnO2纳米线形貌及场发射性能影响

采用化学气相沉积法系统研究了合成温度和N₂/O₂流量对生长在碳纤维衬底上的SnO₂纳米线形貌及场发射性能的影响规律. 利用扫描电镜(SEM)、透射电镜(TEM), X射线衍射(XRD)及能谱仪(EDS)对产物细致表征, 结果表明, SnO₂纳米线长径比随反应温度的升高而增大; 随N₂/O₂流量比值的增大先增大后变小, 场发射测试表明, 合成温度780 ℃, N₂/O₂流量比为300 : 3 时SnO₂纳米线阵列具有最佳的场发射性能, 开启电场为1.03 V/μm, 场强增加到1.68 V/μm时, 发射电流密度达0.66 mA/cm², 亮度约2300 cd/m².     

A novel strategy to synthesize cobalt hydroxide and Co3O4 nanowires

Cobalt hydroxide ultra fine nanowires were prepared by a facile hydrothermal route using hydrogen peroxide. This method provides a simple, low cost, and large-scale route to produce β-cobalt hydroxide nanowires with an average diameter of 5 nm and a length of ca. 10 μm, which show a predominant well-crystalline hexagonal brucite-like phase. Their thermal decomposition produced highly uniform nanowires of cobalt oxide (Co₃O₄) under temperature 500 °C in the presence of oxygen gas. The produced cobalt oxide was characterized by X-ray diffraction, transmission electronic microscopy, and selected-area electron diffraction. The results indicated that cobalt oxide nanowires with an average diameter of 10 nm and a length of ca. 600 nm have been formed, which show a predominant well-crystalline cubic face-centered like phase.     

A novel method to synthesize homogeneous and mono-dispersible CeO<Subscript>2</Subscript> nanospheres: two-step hydrothermal process

In this study, homogeneous mono-disperse CeO₂ nanosphere was successfully synthesized through two-step hydrothermal process, and the degree of sphericity was also improved comparing with the sample synthesized through one-step hydrothermal process. In the whole reaction, crystallization and ripening were regarded as two independent stages. Upper-layer transparent solution obtained through centrifugation after first-step hydrothermal process contained a large number of CeO₂ crystal seeds, indicating that crystallization has taken place in this stage. Then, these seeds participated in the second hydrothermal process and ripened into homogeneous spheres finally. In addition, poly(vinylpyrrolidone) was applied as surfactant to facilitate the oriented aggregation of small CeO₂ nanoparticles into nanospheres. The formation mechanism was discussed through scanning electron microscopy and transmission electron microscopy.     

Growth Mechanism and Characterization of Single-crystalline Ga-doped SnO2 Nanowires and Self-organized SnO2/Ga2O3 Heterogeneous Microcomb Structures

Ga掺SnO2单晶纳米线和SnO2/Ga2O3自组织异质微米梳是通过简单的热蒸发沉淀法一步制得的,并通过X射线粉末衍射(XRD)、场激发扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、X射线能量散射谱仪(EDS)、选区电子衍射谱(SAED)进行表征．从FE-SEM的图片上可以看出生成的产物具有纳米线和一种新的微米梳状形貌．XRD、SAED和EDS显示他们是单晶四角形的SnO2．产物的主干呈带状,纳米带阵列均匀的分布在主干的一侧或两侧．大量的Ga2O3纳米颗粒沉积在微米梳的表面．主干纳米带主要沿着[100]方向生长, 自组织的纳米带分支则在主干的(100)面上沿着[110]或者[110]方向生长．由于Ga的大量掺杂,光致发光谱的衍射峰发生红移并严重变宽．针对SnO2:Ga2O3异质微米梳的生长过程进行了解释,并讨论了实验条件对形貌的影响．     

SnO2:Zr薄膜对SO2气体的光学气敏特性研究

采用双靶反应溅射制得SnO₂:Zr薄膜,并对它作了150°C下SO₂气敏光学特性试验,首次发现在适当工艺条件下制得的SnO₂:Zr薄膜在近红外波段(1.7～3μm)对SO₂气体具有明显的光学气敏特性,在2.65μm附近透过率上升幅度达10%左右.Zr的引入增强了SnO₂薄膜对SO₂的吸附能力.用二次离子质谱对吸附SO₂前后的薄膜作了组分相对含量分析.本实验结果对今后研究高性能SO₂气敏传感器有一定的价值.     

In-situ bridging of SnO2 nanowires between the electrodes and their NO2 gas sensing characteristics

A simple and efficient way of making highly sensitive SnO₂ nanowire-based gas sensors without an individual lithography process was studied. The SnO₂ nanowires network was floated upon the Si substrate by separating the Au catalyst layer from the substrate. As the electric current is transported along the networks of the nanowires, not along the surface layer on the substrate, the gas sensitivities could be maximized in this networked and floated structures. The sensitivity was 5-30 when the NO₂ concentration was 1-10 ppm. The response time was ca. 20-60 s.     

氧氩比对SnO2/Ag/SnO2透明导电膜光电性能的影响

在室温及不同的氧氩比条件下,采用射频磁控溅射Ag层和直流磁控溅射SnO₂层,在载玻片衬底上制备出了SnO₂/Ag/SnO₂多层薄膜.用霍尔效应测试仪、四探针电阻测试仪和紫外-可见-近红外光谱仪等表征了薄膜的电学性质和光学性质.实验结果表明:当氧氩比为1:14时,所制得的薄膜的光电性质优良指数最大,为1.69×10^-2 Ω^-1;此时,薄膜的电阻率为9.8×10^-5 Ω·cm,方电阻为9.68 Ω/sq,在400~800 nm可见光区的平均光学透射率达85%;并且,在氧氩比为1:14时,利用射频磁控溅射Ag层和直流磁控溅射SnO₂层在PET柔性衬底上制备出了光电性质优良的柔性透明导电膜,其在可见光区的平均光学透过率达85%以上,电阻率为1.22×10^-4 Ωcm,方电阻为12.05 Ω/sq.