Physicochemical investigations of Pd2+ substituted ZnO nanoflowers for liquefied petroleum gas sensing

Journal of Materials Science: Materials in Electronics - Present study portrays, physicochemical investigations of pristine and Pd2+ modified ZnO nanoflowers (NFs) compositional series...     

Sm3+ photoluminescence in co-sputtered SiO2 thin films

Thin films of SiO₂ containing Sm were deposited by magnetron co-sputtering. The concentration of Sm in the films was varied by changing the amount of Sm placed on the fused silica target. The samarium content in the films was established by Rutherford back-scattering measurements. Photoluminescence (PL) was excited with the 488-nm line of an Ar ion laser. It consists of several lines in the visible, which are assigned to transitions between multiplets of Sm³⁺. The concentration dependence of the PL intensity was studied. It passes through a maximum and decreases at higher Sm content. The films were annealed in vacuum at temperatures between 300 and 1000 °C. There was a strong increase in the PL intensity after annealing at 600 °C, and then it fell again after annealing at 1000 °C. The data are compared to spectra of Sm³⁺ in other matrices. The mechanisms of PL excitation and quenching are discussed.     

SnO2纳米晶修饰多孔Co3O4纳米棒的制备及气敏性能研究

以CoCl2.6H2O和CO(NH2)2为原料采用水热法合成多孔Co3O4纳米棒,之后通过自组装的方法将SnO2纳米晶修饰到多孔Co3O4纳米棒上。研究了SnO2纳米晶修饰对多孔Co3O4纳米棒气敏性能的影响。气敏测试结果表明SnO2纳米晶的修饰明显增强了多孔Co3O4纳米棒对CH3CH2OH和H2S的响应,对CH3CH2OH和H2S的检出下限分别达到5.0×10-6和1.0×10-6。     

Spectroscopic properties of Sm3+-doped oxy-fluoride powders with various Sm3+ concentration and sintering temperature

Sm³⁺-doped oxy-fluoride (OFSm) powders are prepared by the melt quenching technique and characterized using FE-SEM, optical absorption and emission techniques. Spectroscopic properties of Sm³⁺-doped oxy-fluoride powders with different Sm³⁺ concentration and sintering temperature are presented and discussed by using the absorption, emission measurements. The Judd–Ofelt intensity (J–O) parameters (Ω_λ, where λ = 2, 4 and 6), measured from the experimental oscillator strengths of the absorption spectra, are used to evaluate the radiative parameters of the fluorescence transitions. Intense orange emission can be obtained when excited with 325 nm wavelength by increasing the sintering temperature to 1400 °C. Ratio of fluorescence intensities arising from the two closing lying ⁴F_3/2 and ⁴G_5/2 levels is studied, concentration quenching has been noticed beyond 2 mol% of Sm³⁺ ions concentration. The excellent spectroscopic properties along with the outstanding thermal stability suggest that the OFSm03 powders may become an attractive laser material to exhibit efficient visible lasing emission in the orange spectral region.     

Up-conversion fluorescence of Tm3+ and Gd3+ in Yb3+/Tm3+ co-doped Gd2O3 nanocrystals

Through a co-precipitation method Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were synthesized. After sintered at 900 degrees C for 1 h in air, the as-prepared Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were converted into Gd2O3:20%Yb3+, 1% Tm3+ nanocrystals. Crystalline phases, sizes, and morphologies of the two samples were characterized by X-ray diffraction and field emission scanning electron microscope. The up-conversion (UC) fluorescence spectra of the Gd2O3:20%Yb3+, 1%Tm3+ nanocrystals were recorded by using a fluorescence spectrophotometer with a 980 nm continuous wave laser diode as excitation source. The nanocrystals not only present characteristic blue and ultraviolet (UV) UC emissions of activated Tm3+, but also show UV UC emissions of host Gd3+. The experimental study suggests that the excitation power has great effects on UC fluorescence properties and the energy transfer from Tm3+ to Gd3+ is very efficient.     

Dielectric properties and relaxation behavior of Sm substituted SrTiO3 ceramics

Sr_1–1.5xSm_xTiO₃ (x = 0–0.025) ceramics were fabricated by the conventional solid-state reaction method. Experimental results show that all ceramics are pure cubic perovskite structure, and the lattice parameters and average grain sizes of the ceramics decrease with the Sm concentration increasing. Compared with the pure SrTiO₃ ceramics, the relative dielectric constant could be enhanced to 3,681 (at 1 kHz and room temperature)with dielectric loss less than 0.02 when x = 0.02. The good stability of ε _r under 0–20 kV/cm is beneficial to applying in high voltage conditions. Two sets of relaxation peaks of Sm doped SrTiO₃ ceramics are observed which are all related to the oxygen vacancies. The medium-temperature relaxation is ascribed to the coupling of oxygen vacancies with strontium vacancies and the origin of high-temperature relaxation is the motion of oxygen vacancies.     

Resistive-switching memory effect of hybrid structures with polyimide and SnO2 nanocrystals

Hybrid memory devices with polyimide and SnO2 nanocrystals on a flexible polyethersulphone substrate have shown a memristor behavior from current-voltage (I-V) measurements. The resistive-switching effects with a current bistability appeared during cycling voltage sweeping within the range of +/- 4 V. This I-V switching effect might have originated from a resistance fluctuation due to the charge trapping into the SnO2 nanocrystals as well as the oxygen vacancies of the ZnO layer and aluminum oxides that were formed between the polyimide and the interface of the Al gate electrode. In the bipolar resistance-switching behavior, the ratio of the high- and low-resistance state currents was about 3.7 x 10(4) at 1 V.     

Optical spectroscopy of Eu3+ ions in tetragonal ZrO2 nanocrystals

A facile solvothermal method was introduced to incorporate Eu3+ ions into the monodisperse tetragonal ZrO2 nanocrystals (NCs) with small size of approximately 4 nm. The optical properties for Eu3+ doped ZrO2 NCs were investigated in detail by using the photoluminescence (PL) spectroscopy at room and low temperatures. Intense red emissions from Eu3+ ions could be achieved via the host sensitization, which was found to be much more efficient than the direct excitation of lanthanide ions. Moreover, multiple sites of Eu3+ as well as the host-to-Eu3+ energy transfer were also revealed based on the PL analyses.     

Eu3+和Sm3+共掺杂TiO2光催化剂的协同效应

采用溶胶-凝胶法制备了纯TiO2和Eu3+/Sm3+共掺杂TiO2复合粉体,采用XRD,DRS和SEM等技术进行表征,以亚甲基蓝(methylene blue,MB)的光催化降解为目标反应,评价了其光催化活性,探讨了Eu3+/Sm3+共掺杂对TiO2粉体光催化的影响机制.结果表明,Eu3+/Sm3+共掺杂可以显著提高TiO2粉体光催化活性,Eu3+/Sm3+共掺杂在TiO2粉体中产生协同作用,可以抑制TiO2由锐钛矿相向金红石相转变,使TiO2的粒径减小.Eu3+/Sm3+共掺杂增大了TiO2粉体的晶格畸变,使TiO2粉体吸收带边蓝移.当Eu3+/Sm3+的掺杂量分别为0.05%和0.1%,TiO2光催化活性最高,光催化降解率达到84.8%.     

Site-selective spectroscopy in Sm(3+)-doped sol-gel-derived nano-glass-ceramics containing SnO(2) quantum dots

Nano-glass-ceramics of composition 95SiO(2)-5SnO(2) doped with 0.4 Sm(3+) (mol%) were synthesized by the thermal treatment of precursor sol-gel glasses. Structural and luminescence measurements were carried out. The precipitated SnO(2) nanocrystals in the glass matrix constitute a wide bandgap quantum-dot system with size comparable to the bulk exciton Bohr radius. A site-selective excitation, by energy transfer from the semiconductor host, reveals that a fraction of the Sm(3+) ions are incorporated in the SnO(2) nanocrystals, whereas the rest remains in the silica glassy phase. An evolution in the Sm(3+) emission spectra has been observed when the SnO(2) nanocrystals are excited with different UV wavelengths, which has been ascribed to selective excitation of nanocrystal sets with predetermined size.     

Hydrothermal synthesis of Eu3+-doped Y2Sn2O7 nanocrystals

Fine powders of Y₂Sn₂O₇ nanocrystals with pyrochlore structure have been successfully synthesized by the hydrothermal method in an alkaline system. The samples were characterized by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. Furthermore, photoluminescence characterization of the Y₂Sn₂O₇ nanocrystals doped with 5 mol% Eu³⁺ was carried out, and the results show that there were some intense and prevailing emission peaks located at 580–635 nm.     

Sm3+:ZnO-B2O3-Al2O3-SiO2系透明玻璃陶瓷的制备和表征

采用熔融和晶化技术合成出含ZnAl2O4微晶的Sm3+:ZnO-B2O3-Al2O3-SiO2(ZBAS)玻璃陶瓷材料,并通过DSC、XRD、SEM和UV-Vis-Nir分光光度计和傅里叶变换荧光光谱仪等对样品进行了表征.结果表明,玻璃陶瓷主晶相为ZnAl2O4,晶相粒径为30nm;可见光透过率为最高可达70％,近红外透过率为70％～85％.该玻璃陶瓷能够受激发射出红光,且发光强度高于同组分的玻璃.     

Luminescence properties of SnO2 nanoparticles dispersed in Eu3+ doped SiO2 matrix

SnO2 nanoparticles dispersed in Eu3+ doped silica (SnO2-SiO2:Eu3+) were prepared at a low temperature (185 degrees C) in ethylene glycol medium. Transmission electron microscopy studies on as-prepared samples have established that SnO2 nanoparticles having size of 4.6 nm are uniformly covered by the SiO2 matrix. Significant extent of exciton mediated energy transfer between SnO2 and Eu3+ ions in heat treated SnO2-SiO2:Eu3+ samples has been attributed to the diffusion of Eu3+ ions from the SiO2 matrix to the near vicinity of SnO2 nanoparticles and its incorporation in the SnO2 matrix. On the other hand, very weak energy transfer exists for SnO2:Eu3+ nanoparticles heated at different temperatures due to the phase segregation of Eu3+ ions from the matrix.     

Growth of SnO(2) nanocrystals controlled by erbium doping in silica

We investigate the effects of erbium doping on SnO(2) nanoclustering in Sn-doped silica. Vibrational spectroscopy data from Raman and infrared absorption measurements show nanostructuring effects on the SnO(2) nanophase. Ultraviolet absorption spectra evidence a gap shift ascribable to size-dependent quantum confinement, also suggesting a role of erbium doping in determining cluster sizes and the amount of localized states on the nanophase boundary. Transmission electron microscopy confirms and details the spectroscopic data. As a result of these measurements, we find that the nanocrystal size distribution becomes narrower, increasing the erbium concentration, while the density of localized states at the nanocrystal surface decreases. The distribution of erbium ions among the possible environments is then examined through simultaneous spectroscopy of luminescence excited by nanocrystal-to-erbium energy transfer and the absorption of nanocrystal luminescence by erbium ions. This analysis shows that erbium behaves as an extrinsic nucleation centre of the SnO(2) nanophase at low doping levels, whereas at high concentrations it modifies the matrix, hindering the growth of SnO(2) crystals and passivating the interface.     

Luminescence of Sm2+ in strontium haloborates

The luminescence properties of Sm²⁺ in Sr₂B₅O₉R (R=Cl, Br) have been studied and compared with those in SrB₄O₇. In the range from 80 to 300 K the emission of Sm²⁺ in Sr₂B₅O₉R is predominantly due to the 4f⁵5d → 4f⁶ transition, while SrB₄O₇ : Sm²⁺ shows a very efficient emission of the 4f⁶ → 4f⁶ type. Differences in the luminescence of Sm²⁺ in the strontium haloborates and tetraborate are discussed.     

Adiabatic demagnetization of Er3+ or Nd3+ substituted YAG

The paramagnetic salts, eg alums, usually employed in adiabatic demagnetization experiments are inconvenient because of their tendency to dehydration, etc. The refractive oxides with magnetic impurities seem to be more favourable. The authors describe the results obtained with Er³⁺ and Nd³⁺ substituted yttrium aluminium garnets (YAG). Final temperatures reached after adiabatic demagnetization are comparable to those obtained with cerium magnesium nitrate. The paper illustrates the possible use of Er³⁺ and Nd³⁺ substitued in YAG for creating a very simple device for obtaining low temperatures in the mK region by adiabatic demagnetization.     

Sm~(3+)/Dy~(3+)掺杂太阳能电池盖板玻璃的性能

采用高温熔融法制备了稀土离子Sm~(3+)和Dy~(3+)掺杂的硅酸盐玻璃,研究了该玻璃的光学性能和光电转换性能,测试了其用作太阳能电池盖板时对电池光电转换效率的影响,并与空白玻璃样品进行对比。结果表明:稀土玻璃样品可见光透过率良好,其在紫外光区域内不同波段光的激发下,以下转换的方式辐射出多个可见光发射峰,其中主要的发射峰波长为484、574、600和646nm等;样品用作电池盖板后,单/非晶硅电池片光电转换效率均有所提高,较相应的空白玻璃/电池组件分别增加了0.07%及0.013%,即稀土玻璃具有将紫外光转换为可见光并提高电池片光电转换效率的作用。