Investigation of structural, morphological, luminescent and thermal properties of combusted aluminium-based iron oxide

Nanocomposites of aluminium integrated hematite α-Fe₂O₃ are synthesized by combustion route using aqueous solutions of AR grade ferric trichloride and aluminium nitrate as precursors. The influence of aluminium incorporation on to the morphology, XPS, photoluminescence and thermal properties has been investigated. The FESEM and AFM micrographs depict that the samples are compact and have homogeneously distributed grains of varying sizes (∼20-60 nm). Chemical composition and valence states of constituent elements in hematite are analyzed by XPS. In room temperature photoluminescence (PL) study, we observed strong violet emission around 436 nm without any deep-level emission and a small PL FWHM indicating that the concentrations of defects are responsible for deep-level emissions. The specific heat and thermal conductivity study shows the phonon conduction behavior is dominant. We studied interparticle interactions using complex impedance spectroscopy. We report a new potential candidate for its possible applications in optoelectronics and magnetic devices.     

The preparation and characterization of La doped TiO2 nanoparticles and their photocatalytic activity

In this paper, pure and La doped TiO₂ nanoparticles with different La content were prepared by a sol-gel process using Ti (OC₄H₉)₄ as raw material, and also were characterized by XRD, TG-DTA, TEM, XPS, DRS and Photoluminescence (PL) spectra. We mainly investigated the effects of calcining temperature and La content on the properties and the photocatalytic activity for degrading phenol of as-prepared TiO₂ samples, and also discussed the relationships between PL spectra and photocatalytic activity as well as the mechanisms of La doping on TiO₂ phase transformation. The results showed that La³⁺ did not enter into the crystal lattices of TiO₂ and was uniformly dispersed onto TiO₂ as the form of La₂O₃ particles with small size, which possibly made La dopant have a great inhibition on TiO₂ phase transformation; La dopant did not give rise to a new PL signal, but it could improve the intensity of PL spectra with a appropriate La content, which was possibly attributed to the increase in the content of surface oxygen vacancies and defects after doping La; La doped TiO₂ nanoparticles calcined at 600°C exhibited higher photocatalytic activity, indicating that 600°C was an appropriate calcination temperature. The order of photocatalytic activity of La doped TiO₂ samples with different La content was as following: 1>1.5>3>0.5>5>0 mol%, which was the same as the order of their PL intensity, namely, the stronger the PL intensity, the higher the photocatalytic activity, demonstrating that there were certain relationships between PL spectra and photocatalytic activity. This could be explained by the points that PL spectra mainly resulted from surface oxygen vacancies and defects during the process of PL, while surface oxygen vacancies and defects could be favorable in capturing the photoinduced electrons during the process of photocatalytic reactions.     

Surface Modification of TiO2 Nanoparticles with Vitamin B12: Relationships between Vitamin B12 Content and Its Optical Properties

Anatase TiO₂ nanoparticles (NPs) with particle size of 10–20 nm were prepared via sol gel technique. The as‐synthesized NPs were immerged in vitamin B₁₂ (VB₁₂) solutions with different concentrations. The in‐ fluences of the solution concentration on photoluminescence and photocatalytic activity of the modified NPs were studied. Fourier transform infrared spectroscopy (FTIR) results demonstrated that TiO₂ NPs adsorb VB₁₂ molecules and that a new band is formed at ～2300 cm^?1. The VB₁₂ loading process led to dimin‐ ishing of the aggregation of NPs and formation of a fibre shape structure. The best photoactivity and PL effect among the modified samples was related to sample ‘d’. The optimum processing conditions to achieve this sample was found to be VB₁₂ concentration of 5 g/L.     

Reusable sensor based on functionalized carbon dots for the detection of silver nanoparticles in cosmetics via inner filter effect

We report a low cost selective analytical method based on inner filter effect (IFE) for citrate-silver nanoparticle (cit-AgNP) detection, in which fluorescent amine-derivatized carbon dots (a-CDs) act as the donor and aggregated cit-AgNPs as the energy receptor. Carbon dots (CDs) were chemically modified with ethylenediamine (EDA) moieties via amidic linkage displaying an emission band at 440 nm. The presence of cit-AgNPs produces a remarkably quenching of a-CD fluorescence via IFE, since the free amine groups at CD surface induce the aggregation of cit-AgNPs accompany by a red-shifting of their characteristic plasmon absorption wavelength, which resulted in “turn-on” of the IFE-decreased in CD fluorescence. The proposed method, which involves the use of chelating agents for removal of metal ions interferences, exhibits a good linear correlation for detection of cit-AgNPs from 1.23 × 10⁻⁵ to 6.19 × 10⁻⁵ mol L⁻¹, with limits of detection (LOD) and quantification (LOQ) of 5.17 × 10⁻⁶ and 1.72 × 10⁻⁵ mol L^−1, respectively. This method demonstrates to be efficient and selective for the determination of cit-AgNPs in complex matrices such as cosmetic creams and reveals many advantages such as low cost, reusability, high sensitivity and non time-consuming compared with other traditional methods.     

掺杂Ce的TiO_2纳米粒子的光致光及其光催化活性

采用sol-gel法制备了纯的和掺杂不同量Ce的TiO_2纳米粒子，并利用XRD， TEM，BET，XPS和PL光谱对样品进行表征，主要考察焙烧温度和含量对掺杂Ce的 TiO_2纳米粒子性质以及光催化降解苯酚活性的影响，并探讨了Ce的掺杂对TiO_2相 变的作用机制以及PL光谱与光催化活性的关系，结果表明，掺杂的Ce~(4+)没有进 入到TiO_2晶格中，而是以小团簇的CeO_2化学态均匀地弥散在TiO_2纳米粒子中， 这可能导致了Ce的掺杂对TiO_2的相变有很大的抑制作用；Ce的掺杂没有引起新的 光致发光现象，而适量Ce的掺杂能够降低TiO_2纳米粒子PL光谱的强度，这是因为 掺杂的Ce~(4+)易于捕获光生电子而生成Ce~(3+);600℃处理的掺杂Ce的TiO_2纳米 粒子表现出较高的光催化活性，这说明600℃是比较合适的焙烧温度，而掺杂不同 量的Ce的TiO_2样品的光催化活性顺序是：3 mol%＞4 mol%＞2 mol%＞5 mol%＞1 mol%＞0 mol%，这与它们的PL光谱强度的顺序是相反的，即PL光谱强度越低，其 光催化活性越高，这说明PL光谱与其光催化活性间有着必然的联系，这是因为掺杂 剂Ce~(4+)能够捕获光生电子，在光致发光过程中使PL光谱强度下降，而在光催化 反应过程中使有机污染物加快氧化。     

Oxygen-crosslinked polysilane: the new class of Si-related material for electroluminescent devices

The preparation and optical properties of the novel silicon-related material named oxygen-crosslinked polysilane were investigated. The oxygen-crosslinked polysilane was prepared by the thermal annealing of the precursor polysilane bearing alkoxyl groups. The photoluminescence consisting of a broad visible band at about 440 nm and a relatively sharp band at about 360 nm was observed at room temperature. The relative intensities of the visible emission were changed during the crosslinking. The visible emission was greatly affected by the steric hindrance of the alkoxyl groups of the precursor. The visible electroluminescene (EL) was also observed uniformly from the EL cell consisting of the oxygen-crosslinked polysilane film sandwiched between A1 electrode and indium-tin-oxide (ITO) electrode. The current densities of the EL cell increased with an increase in the oxygen-crosslinking. © 1997 John Wiley & Sons, Ltd.     

Effect of bismuth on liquid-phase epitaxy (LPE) grown GaAs layer using Ga–As–Bi melt

GaAs epitaxial layers of high structural quality have been realised from Ga–As–Bi melt using liquid-phase epitaxy (LPE). LPE grown GaAs epitaxial layer using bismuth solvent on GaAs substrate has been found to be of good structural perfection as compared to layers using gallium solvent. The temperature-dependent PL spectra of GaAs layer, grown from Ga+Bi mixed solvent has shown that the use of bismuth does not change the band energy. ECV depth profile of heavily zinc-doped epitaxial layer shows uniform doping in the GaAs layer grown using gallium solvent as compared to the layer grown using bismuth solvent.     

Deposition of ZnO multilayer on LiNbO3 single crystals by DC-magnetron sputtering

Zinc oxide (ZnO) thin films were deposited on LiNbO₃ (LN) single crystals with 200 nm thicknesses by three different ways, where coating of zinc (Zn) film was followed by thermal oxidation for four, two, and one steps with 50, 100, and 200 nm thicknesses repeatedly. Sample, which was produced at 4-step of deposition and oxidation of Zn layer, showed high transmittance and low structural defect due to a lower photoluminescence intensity and Urbach energy. Average grain size in X-ray diffraction (XRD), scanning electron microscopy (SEM) micrograph, and atomic force microscopy (AFM) images for multilayer of ZnO was lower than monolayer of ZnO thin films. Applying multilayer coating technique leads to decrease of surface roughness and scattering on light on surface and fabrication of LiNbO₃ waveguides with lower optical loss.     

退火对He注入及随后208Pb27+辐照的Al2O3单晶PL谱的影响

利用高能离子研究了110 keV 的He⁺注入Al₂O₃单晶及随后230 MeV的²⁰⁸Pb²⁷⁺辐照并在不同温度条件下退火样品的光致发光的特性. 从测试结果可以清楚地看到在375 nm，390 nm，413 nm 和450 nm 出现了强烈的发光峰. 经过600 K退火2 h后测试结果显示，390 nm发光峰增强剧烈，而别的发光峰显示不明显. 在900 K退火条件下，390 nm的发光峰开始减弱相反在510 nm出现了较强的发光峰，到1100 K退火完毕后390 nm的发光峰完全消失，而510 nm的发光峰相对增强. 从辐照样品的FTIR谱中看到，波数在460—510 cm^-1间的吸收是振动模式，经过离子辐照后，吸收带展宽，随着辐照量的增大，Al₂O₃振动吸收峰消失，说明Al₂O₃振动模式被完全破坏. 1000—1300 cm^-1之间为Al-O-Al桥氧的伸缩振动模式，辐照后吸收带向高波数方向移动. 退火后的FTIR谱变化不大.     

HigHighly strained InGaAs/GaAs quantum wells emitting beyond 1.2 µm

Highly strained In_xGa_1–xAs quantum wells (QWs) with GaAs barriers emitting around 1.2 µm are grown on GaAs substrates by metal organic vapour phase epitaxy (MOVPE) at low growth temperatures using conventional precursors. The effects of growth temperature, V/III ratio and growth rate on QW composition and luminescence properties are studied. The variation of indium incorporation with V/III ratio at a growth temperature of 510 °C is found to be opposite to the results reported for 700 °C. By an appropriate choice of the growth parameters, we could extend the room temperature photoluminescence (PL) wavelength of InGaAs/GaAs QWs up to about 1.24 µm which corresponds to an average indium content of 41% in the QW. The results of the growth study were applied to broad area laser diodes emitting at 1193 nm with low threshold current densities. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)