Photoluminescence and field-emission properties of Cu-doped SnO2 nanobelts

By using a thermal evaporation and condensation method, Cu-doped SnO₂ nanobelts were synthesized on silicon substrate. High-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy studies of Cu-doped SnO₂ nanobelts demonstrate that the nanobelts are single-crystal structures and Cu is homogeneously doped into the SnO₂ lattice. X-ray diffraction further confirmed the single-phase nature of these nanobelts. The photoluminescence measurements of the nanobelts and samples annealed in oxygen were measured from 77 K to 300 K. Field-emission measurements demonstrated that the Cu-doped nanobelts possessed good performance with a turn-on field of ∼2.9 V/μm and a threshold field of ∼4.8 V/μm.     

Photoluminescence of CdS nanoparticles embedded in a starch matrix

CdS nanoparticles were synthesized by precipitation in aqueous solution using starch as the capping molecule, and the effect of the pH of the solution on the optical absorption, photoluminescence, and size of the nanoparticles was studied. Absorption spectra, obtained by photoacoustic spectroscopy, indicated that the band gap energy of the crystalline nanoparticles decreased from 2.68 eV down to 2.48 eV by increasing the pH of the solution from 9 up to 14. The X-ray diffraction analysis revealed that the CdS nanoparticles were of zinc blende structure, and that the particle size increased from 1.35 nm up to 2.45 nm with increasing pH. In addition, temperature-dependent photoluminescence (PL) measurements of the capped material showed a blue-shift of the emission peak for temperatures higher than 150 K, indicating the influence of starch on the formation of defect levels on the surface of the CdS nanoparticles.     

Photoluminescence spectroscopy of CdSe nanoparticles embedded in transparent glass

In this paper we present photoluminescence measurements of CdSe nanoparticles embedded in transparent glass. Sample is prepared using an original technique, which combines both heat treatment and ultraviolet laser irradiation. Photoluminescence spectra displayed one main emission band at 2.14 eV. We identify this bands energy as basic interband transition in CdSe nanoparticle. We calculated energy of basic (1s_h–1s_e) transition in spherical CdSe quantum dot (QD), within infinite potential barrier, in effective-mass approximation. On the basis of this model, average radius of synthesized CdSe QDs is about 3 nm, which is in consistence with AFM measurements and UV–VIS absorption measurements.     

SnO2纳米晶体的制备、结构与发光性质

使用软化学方法在碱性溶液中制备出了颗粒尺寸分布均匀的SnO2纳米颗粒,使用透射电子显微镜(TEM)、X射线衍射(XRD)、光致发光谱(PL)和光吸收谱等方法分析与表征了SnO2纳米颗粒的结构和光学性能.实验中通过表面活性剂的加入来控制纳米颗粒的结晶与凝聚.XRD,TEM的结果表明,原始制备出的SnO2纳米颗粒的平均粒径小于4 nm,为完好的晶体状态.纳米颗粒经过400-1000 ℃退火后晶粒尺寸进一步增大.光吸收谱表明,相对于体材料,纳米颗粒的禁带宽度展宽并随颗粒尺寸增大而红移.光致发光谱测试表明,不同温度下退火的SnO2纳米颗粒在350-750 nm有较强的发光,研究表明这是来源于颗粒表面的氧空位缺陷发光.     

Enhanced dielectric properties of polyvinylidene fluoride with addition of SnO2 nanoparticles

In this letter, SnO₂/polyvinylidene fluoride (PVDF) nanocomposites with outstanding dielectric properties were fabricated. The SEM and TEM images showed that SnO₂ nanoparticles with size of 5–7 nm dispersed homogeneously in polymer matrix. The significantly improved dielectric constant was well explained by percolation theory. The nanocompo‐ sites can retain a certain value of breakdown field. The maximum energy density of SnO₂/PVDF nanocomposites was 5.4 J/cm³, two times that of the pure polyvinylidene fluoride. These findings suggest that SnO₂/PVDF nanocomposites are suitable candidates for energy storage applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Photoluminescence and photoconducting properties of ZnO nanoparticles

Photoluminescence and photoconducting properties of thinfilms of colloidal ZnO nanoparticles have been investigated by annealing them in an oxygen atmosphere at different temperatures. The changes in the defect-related emission and the photoconducting properties with the annealing temperature have been examined in detail.     

Role of chelating agent in chemical and fluorescent properties of SnO2 nanoparticles

A modified polyacrylamide gel route is applied to synthesize SnO2 nanoparticles. High-quality SnO2 nanoparticles with a uniform size are prepared using different chelating agents. The average particle size of the samples is found to depend on the choice of the chelating agent. The photoluminescence spectrum detected at λex = 230 nm shows a new peak located at 740 nm due to the surface defect level distributed at the nanoparticle boundaries.     

Structural,dielectric and photoluminescence properties of co-precipitated Zn-doped SnO2 nanoparticles

Zn-doped SnO₂ nanoparticles were prepared by the chemical co-precipitation route. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses of these prepared nanoparticles were carried out for structural and morphological studies. All the samples have been found to have tetragonal rutile structure of the polycrystalline SnO₂ having crystallite size in the range 13–25 nm. TEM micrographs show agglomeration of nanoparticles in all the samples. At a particular temperature, the dielectric constant of all the samples has been found to decrease with increasing frequencies which may be due to rapid polarization processes occurring in SnO₂ nanoparticles. The ac conductivity, σ (ω), has been found to vary with frequency according to the relation σ (ω) ∝ ω^S. The value of S has been found to be temperature dependent, decreasing with increasing frequency which suggests that a hopping process is the most likely conduction mechanism in these nanoparticles. The room temperature photoluminescence (PL) spectra of the undoped and Zn-doped SnO₂ nanoparticles consist of the near band-edge ultraviolet (UV) emission and the defect related visible emissions. The origin of emission peaks in the visible region is attributed to oxygen-related defects that are introduced during growth.     

氧化锡纳米线的拉曼光谱和光致发光光谱研究

用表面限制剂对水热法生成的前驱物加以限制生长的方法成功制备了氧化锡纳米线结构,TEM和HRTEM的结果表明该纳米线由沿[001]方向生长的氧化锡单晶组成,纳米线直径在5-10纳米、长度100-500纳米。利用拉曼光谱和发光光谱对其生长过程和发光现象进行了详细的研究,结果表明,细长的氧化锡纳米线出现356、515、691 cm-1新的拉曼振动模以及600 nm较强的光致发光。     

Photoluminescence properties of powder and pulsed laser-deposited PbS nanoparticles in SiO2

Thin films of lead sulfide (PbS) nanoparticles embedded in an amorphous silica (SiO₂) host were grown on Si(1 0 0) substrates at different temperatures by the pulsed laser deposition (PLD) technique. Surface morphology and photoluminescence (PL) properties of samples were analyzed with scanning electron microscopy (SEM) and a 458 nm Ar⁺ laser, respectively. The PL data show a blue-shift from the normal emission at ∼3200 nm in PbS bulk to ∼560-700 nm in nanoparticulate PbS powders and thin films. Furthermore, the PL emission of the films was red-shifted from that of the powders at ∼560 to ∼660 nm. The blue-shifting of the emission wavelengths from 3200 to ∼560-700 nm is attributed to quantum confinement of charge carriers in the restricted volume of nanoparticles, while the red-shift between powders and thin-film PbS nanoparticles is speculated to be due to an increase in the defect concentration. The red-shift increased slightly with an increase in deposition temperature, which suggests that there has been a relative growth in particle sizes during the PLD of the films at higher temperatures. Generally, the PL emission of the powders was more intense than that of the films, although the intensity of some of the films was improved marginally by post-deposition annealing at 400 °C. This paper compares the PL properties of powder and pulsed laser-deposited thin films of PbS nanoparticles and the effects of deposition temperatures.     

Conductivity and dielectric studies of Li2SnO3

Lithium stannate (Li₂SnO₃) has been prepared by solution evaporation method. The precursor obtained is sintered at 800°C for 5, 6, and 7?h, respectively. X-ray diffractogram confirmed that the sample obtained after sintering is Li₂SnO₃. The pelletized Li₂SnO₃ after heating at 500?°C for 3?h is used for electrochemical impedance spectroscopy characterization. Impedance measurements have been carried out over frequency range from 50?Hz to 1?MHz and temperature range from 563 to 633?K. The conductivity?Ctemperature relationship is Arrhenian. Several important parameters such as activation energy, ionic hopping frequency and its rate, carrier concentration term, mobile ion number density, ionic mobility, and diffusion coefficient have been determined. The characteristics of log conductivity and log ionic hopping rate against temperature for the system suggest that the conduction and ionic hopping processes are thermally activated. The values of activation energy for conduction and relaxation processes as well as activation enthalpy for ionic hopping are about the same.     

Raman properties embeddedof GaSb nanoparticlesin SiO2 films

The Raman shifts of nanocrystalline GaSb excited by an Ar^ ion laser at wavelengths 514.5, 496.5, 488.0, 476.5,and 457.9nm are studied by an SPEX-1403 laser Raman spectrometer respectively, and they are explained by phonon confinement, tensile stress, resonant Raman scattering and quantum size effects. The Stokes and anti-Stokes Raman spectra of GaSb nanocrystals strongly support the Raman feature of GaSb nanocrystals. The calculated optical spectra compare well with experimental data on Raman scattering GaSb nanocrystals.     

Hole traps and thermoluminescence in Li2B4O7:Be

A trapped-hole centre with a high thermal stability is studied in Li₂B₄O₇:Be. EPR spectrum demonstrates a hyperfine splitting due to interaction of the trapped hole with a ⁹Be nucleus. The hole is trapped at the common vertex (bridging oxygen) of two adjacent BO₄ tetrahedra when Be²⁺ substitutes for B³⁺ in one of them. The centre is stable up to ≈500 K. The high-temperature thermoluminescence peak at 510–575 K occurs when the released holes recombine with trapped electrons. This peak shows an ultraviolet exciton-like luminescence band and also luminescence bands of casual impurities.     

Structural and optical properties of Li substituted CuO nanoparticles

Copper oxide (CuO) is a favorable material for photovoltaic application where lattice defects/distortions play a significant role for shaping its optical and several other physical properties. In this study, pristine and lithium (Li) substituted CuO nanoparticle (1.0, 3.0, 5.0 and 7.0 mol% of Li) have been prepared via an eco-friendly and cost-effective sol–gel method and a systematic study on the effect of Li ion substitution has been drawn. The Rietveld refinement results confirmed the Li ion substitution obsessed structural alteration from monoclinic to tetragonal symmetry (C2/c?→?I4/mmm). It was observed that the C2/c and I4/mmm synchronized phases continues up to 7%. Such structural alteration leads to fascinating optical properties due to destruction of parent phase. Moreover, lithium cations inhibit the crystal growth, which created various types of vacancy/defect states that essentially need to be investigated using SEM, FTIR and Raman spectroscopy. Moreover, we have demonstrated that the native lattice alterations brought by size misalliance amid the host [Cu²⁺ (0.73 Å)] and the dopant [Li?+?(0.76 Å)] and the presence of oxygen vacancies created via Li substitution in CuO also results in the increment of deep level emission in photoluminescence spectra. The obtained results confirmed that Li ion substitution remarkably enhance optical properties, making such materials promising for device applications.     

Photoluminescence and optical absorption properties of silicon quantum dots embedded in Si-rich silicon nitride matrices

Silicon nitride (SiN_x) films were prepared with a gas mixture of SiH₄ and NH₃ on Si wafers using the plasma-enhanced chemical vapor deposition (PECVD) method. High-resolution transmission electron microscopy and infrared absorption have been used to reveal the existence of the Si quantum dots (Si QDs) and to determine the chemical composition of the silicon nitride layers. The optical properties of these structures were studied by photoluminescence (PL) spectroscopy and indicate that emission mechanisms are dominated by confined excitons within Si QDs. The peak position of PL could be controlled in the wavelength range from 1.5 to 2.2 eV by adjusting the flow rates of ammonia and silane gases. Absorbance spectra obtained in the transmission mode reveal optical absorption from Si QDs, which is in good correlation with PL properties. These results have implications for future nanomaterial deposition controlling and device applications.     

Correlated room temperature ferromagnetism and photoluminescence in Al-doped SnO2 nanoparticles

We investigated the single exciton and multiple exciton generation (MEG) behavior in Ag₇ and single Cu atom-doped Ag₇ quantum clusters using ab initio. MEG is observed for the first time in metal clusters. The results indicate that multiple excitons appear in the visible and near ultraviolet light ranges. Single excitations are main contribution for the optical spectra, while the multiple excitons merely contribute for some peaks at the higher energies. However, occurrence of MEG enhances the optical absorption in Ag₇ cluster. The optical spectrum of pure Ag₇ cluster obtained using the symmetry-adapted cluster theory with configuration interaction, and time-dependent density functional theory is in excellent agreement with experiment spectrum. As observed in both single Cu atom-doped Ag₇ clusters, redshifts and suppressions of the MEG-related absorption peaks are observed compared with pure Ag₇ cluster.     

Fluorinated Eu‐Doped SnO2 Nanostructures with Simultaneous Phase and Shape Control and Improved Photoluminescence

Fluorinated Eu‐doped SnO₂ nanostructures with tunable morphology (shuttle‐like and ring‐like) are prepared by a hydrothermal method, using NaF as the morphology controlling agent. X‐ray diffraction, field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and energy dispersive spectroscopy are used to characterize their phase, shape, lattice structure, composition, and element distribution. The data suggest that Eu³⁺ ions are uniformly embedded into SnO₂ nanocrystallites either through substitution of Sn⁴⁺ ions or through formation of Eu‐F bonds, allowing for high‐level Eu³⁺ doping. Photoluminescence features such as transition intensity ratios and Stark splitting indicate diverse localization of Eu³⁺ ions in the SnO₂ nanoparticles, either in the crystalline lattice or in the grain boundaries. Due to formation of Eu‐F and Sn‐F bonds, the fluorinated surface of SnO₂ nanocrystallites efficiently inhibits the hydroxyl quenching effect, which accounts for their improved photoluminescence intensity.