Characterization and luminescence properties of Gd2O3 phosphor

Gd₂O₃ phosphor was synthesized by combustion synthesis using gadolinium nitrate hexahydrate as precursor and urea as fuel. Structural and surface morphology were studied by X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Chemical composition analysis of the phosphor was performed by Fourier-transform infrared spectroscopy, and tts optical properties were characterized by use of photoluminescence (PL) and thermoluminescence (TL) techniques. In PL spectra, feeble emission at 490 nm (blue) and intense emission at approximately 545 nm (green) are observed after excitation at 300 nm. TL measurement was performed on the Gd₂O₃ phosphor by irradiating it with γ-rays (1 kGy). A well resolved glow peak at 226.4 °C was observed. Kinetic data were estimated from the TL glow curve by use of Chen’s peak-shape method; the results are discussed in detail. The average particle size of the Gd₂O₃ phosphor was 41 nm; a monoclinic phase was formed at a firing temperature of 500 °C. This was in agreement with SEM and TEM results.     

Synthesis and optical properties of Gd2O3:Pr3+ phosphor particles

Spherical-shaped Gd₂O₃:Pr³⁺ phosphor particles were prepared with different concentrations of Pr³⁺ using the urea homogeneous precipitation method. The resulting Gd₂O₃:Pr³⁺ phosphor particles were characterized by X-ray diffraction, field emission scanning electron microscope, and photoluminescence spectroscopy. The effects of the Pr³⁺ doping concentration on the luminescent properties of Gd₂O₃:Pr³⁺ phosphors were investigated. Photoluminescence measurements revealed the Gd₂O₃:1?% Pr³⁺ phosphor particles to have the strongest emission. The luminescence properties of Gd₂O₃:Pr³⁺ particles are strongly affected by the phosphor crystallinity and X-ray diffraction measurements confirmed that the crystallinity of Gd₂O₃ cubic structure could be enhanced by increasing the firing temperature. The luminescent Gd₂O₃:Pr³⁺ phosphor particles have potential applications in areas, such as optical display systems, lamps and etc.     

纳米氧化锌的制备与发光性能的研究

Nanocrystalline ZnO Powders were prepared by sol-gel process from Zn(Ac)₂·2H₂O and 2-methoxyethanol solutions containing monoethanolamine. It was found that the photoluminescence (PL) spectra of samples (calcined at 250, 350 and 500 ℃, respectively) had two emission bands in UV region (at ～378 nm) and visible region (at ～502 nm) . The intensity of UV emission bands decreased with the increase of the calcination temperature, and the opposite was true for the visible emission band. TEM, TG-DTG, DTA, XRD, FTIR and surface photovoltage spectra (SPS) were used to investigate this competitive phenomenon. The results indicate that the adsorption of organies on the surface of nanoparticles is the key factor responsible for the relative PL intensity of the two emission bands.     

Photoluminescence of new red phosphor SrZnO2:Eu

SrZnO₂:Eu³⁺ has been synthesized by solid-state reaction and its photoluminescence in ultraviolet (UV)-vacuum ultraviolet (VUV) range was investigated. The broad bands around 254 nm are assigned to CT band of Eu³⁺-O²⁻. With the increasing of Eu³⁺ concentration, Eu³⁺ could occupy different sites, which leads to the broadening of CT band. A sharp band is observed in the region of 110-130 nm, which is related to the host absorption. The phosphors emit red luminescence centered at about 616 nm due to Eu³⁺⁵D₀→⁷F₂ both under 254 and 147 nm, but none of Eu²⁺ blue emission can be observed.     

Photoluminescence investigations of ZnO micro/nanostructures

Zinc oxide (ZnO) is probably one of the most researched wide bandgap semiconductors in the last decades due to its unique characteristics in terms of low production cost, high availability, bioinertness, and especially its interesting optical properties. Although this semiconductor is considered an ‘old’ material and is known to possess such unique properties for more than three decades, the interest was renewed because of the advances in nanotechnology and the possibility to be produced in a vast number of nanostructures with tunable properties. An adequate knowledge of the nanomaterials’ optical response is mandatory for assessing and optimizing their functionalities towards different applications. Although the photoluminescence properties of ZnO bulk materials have been known from several decades, quite a number of open questions remains, namely regarding the nature of defects responsible for the broad luminescence bands frequently observed in the visible spectral region. With the effects of reducing the dimensionality of the material to the nanoscale, changes may arise in the luminescence outcome due to the role of the surface/interface characteristics. Indeed, the surface phenomena can strongly affect the nanostructure properties and can be used to tailor them, consequently having a profound influence on the performance of the devices where the nanostructures are employed. Hence, in this article, an overview of the fundamental properties of ZnO, with emphasis on the main optical recombination mechanisms, both in bulk and at the nanoscale, is provided to disclose some of the current knowledge in this subject. In addition, some examples of the myriad of applications where this semiconductor has been exploited are also discussed.     

Synthesis and Photoluminescence of Eu-doped ZnO Nanosheets

Eu-doped ZnO nanosheets were synthesized successfully by means of the hydrothermal method. The X-ray diffraction(XRD) pattern shows that the sample is a single phase with the ZnO-like wurtzite structure. And the X-ray photoelectron spectrum suggests that there are Eu3+ ions in the matrix of the sample. Eu3+-related red emissions resulted from energy transfer were observed for the nanosheets under UV laser excitation. The UV, green and yellow emissions were also seen in the photoluminescence spectra.     

Photoluminescence and Raman scattering of ZnO nanorods

Zinc oxide (ZnO) nanorods were synthesized by a simple microemulsion method. The photoluminescence (PL) spectra at room temperature were measured. The strong UV excitonic emission indicates the good optical properties, and the weak deep-level emission reveals very limited structural defects in the crystals. The multiple peaks in the PL spectrum obtained at 15 K are assigned to the donor-bound exciton (DBE), free to bound transition (FB) and FB–LO phonon replicas. The temperature dependence of energy, intensity, and linewidth of each emission band confirms the effect of thermal ionization progress of excitons and nonradiative recombination activated thermally. The nonresonant Raman scattering spectra at room temperature were excited by He–Ne laser (wavelength ～632.8 nm). The perfect wurtzite structure in ZnO nanorods has been verified by the intense E₂ modes, which include low and high frequency vibrations. The possible reasons for the red shift and broadening of vibration modes were studied by the resonant Raman scattering spectra at room temperature. The power-dependence of Raman shift and FWHM shows the laser irradiation effect on the vibrational modes.     

Preparation and Photoluminescence of ZnO Nanorods Arrays

A high-density well-aligned Zinc Oxide nanorod array was synthesized on Si (100) substrate by a simplevapor deposition under normal pressure using neither a catalyst and nor pre-deposition of ZnO film. Various different morphologies were obtained in different deposition regions. Si substrate put over the Zn source was the key factor in getting a well-aligned sample. Field emission scanning electron microscope (FESEM) observations and X-ray diffraction were carried out to characterize the surface morphology and crystalline quality of the samples. The growth mechanism is discussed. The photoluminescence properties of the ZnO samples were also investigated. It is suggested that the green band is related to oxygen vacancies and thekinetic process involving transition from shallow donor to deep acceptor level.     

氧化锌纳米点阵列体系的制备及发光性能

A novel nano-masking technique based on porous alumina membrane as mask was developed for preparing ZnO nanodots on Si substrate. The as-deposited nanodots with uniform size were in two-dimensional, regular array, whose regular structure and diameter were closely related to the mask used. Photoluminescence results show that the ZnO nanodot array have a strong UV light emission peak around 380 nm and a wide blue-green light emission peak at 460～610 nm at room temperature. The former corresponds to the near band edge emission of the wide band-gap ZnO and the latter could be attributed to the recombination of a photogenerated hole with singly ionized oxygen vacancy.     

纳米氧化锌及负载沸石的抗菌性能研究

霉变是引起饲料变质的主要因素.目前已知污染饲料的产毒霉菌约100多种,可产生200多种霉菌毒素,其中,黄曲霉菌产生的有毒代谢物黄曲霉毒素（AFT）已成为世界很多地区的主要问题.实践证明,最有效的办法之一是在饲料中添加防霉物质即防霉剂.丙酸盐对于霉菌、酵母菌及细菌具有广泛的抗菌作用,尤其是对黄曲霉等抑制作用比山梨酸钾和苯甲酸钠盐都要强得多,生产成本又较低.因此,早在五、六十年代就已被大多数发达国家作为最重要、最广泛的食品防腐剂使用.但是丙酸受热损失大,不适合制粒,挥发快,防霉持续期比较短,易受钙盐中和而造成活力损失.丙酸腐蚀性强,有刺激性气味,也影响饲料适口性,而且饲料需要在一定的酸性条件下才能发挥防霉的功效[1].由此可见,丙酸类防霉剂有着很多的缺陷,亟待更替.     

Factors Affecting Laser-Excited Photoluminescence from ZnO Nanostructures

The role of defects on laser-excited photoluminescence of various ZnO nanostructures has been investigated. The study shows that defects present in ZnO nanostructures, specially Zn-related defects play a crucial role in determining the laser-excited photoluminescence intensity (LEI). ZnO nanoparticles as well as nanorods (NR) annealed in oxygen atmosphere exhibit remarkable enhancement in LEI. A similar enhancement is also shown by Al-doped ZnO NR.     

一种新颖的ZnO纳米结构的自组装合成及发光性能

采用水热法制备了花生状ZnO微米棒, 通过XRD, EDX和FE-SEM等技术分析了其物相组成、形貌及尺寸; 通过变温荧光光谱测试及对所得谱图的高斯拟合研究了该ZnO微米棒的荧光性能, 并将其在300 K时所得的谱图与常规室温荧光谱图进行了比较. XRD, EDX及FE-SEM测试结果表明, 该产物为长约10 μm, 直径约2 μm的花生状六方纤锌矿ZnO微米棒; 荧光测试结果表明, 该ZnO微米棒有紫外峰、紫峰和绿峰3个发光峰, 当温度从8 K升至300 K时, 各峰的强度均有所减弱, 同时紫外峰出现蓝移, 绿峰出现红移, 紫峰峰位出现特殊的“S”形(红移-蓝移-红移)移动. 并对各峰的产生及随温度变化的规律进行了探讨.     

Photoluminescence enhancement of PEG-modified YAG:Ce3+ nanocrystal phosphor prepared by glycothermal method

Y3Al5O12:Ce3+ (YAG:Ce3+) nanocrystals were synthesized in 1,4-butylene glycol (BG) with and without poly(ethylene glycol) (PEG) by the glycothermal method. The internal quantum efficiency of the photoluminescence (PL) corresponding to the 5d --> 4f transition of Ce3+ in the YAG:Ce3+ nanocrystal increased from 21.3 to 37.9% by addition of PEG, while no appreciable change in the primary particle size, the crystallite size, and the lattice distortion was recognized by transmission electron microscopy and X-ray diffractometry. The thermogravimetry-differential thermal analysis, Fourier transform infrared absorption spectroscopy and 1H --> 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR) confirmed the preferential coordination of PEG to the YAG:Ce3+ nanocrystal. 27Al single-pulse excitation MAS NMR reveals that the ratio of the 4-fold coordination site to the 6-fold coordination site increased from 0.53 to 0.72 by addition of PEG. We conclude that the surface modification of the YAG:Ce3+ nanocrystal by PEG induces the surface passivation, the prevention of the oxidation of Ce3+ to Ce4+, the promotion of the incorporation of Ce3+ into YAG and the local structural rearrangement, resulting in the PL enhancement.     

纳米Ag/ZnO微波辅助合成与微波增强光催化罗丹明B

本文通过微波辅助、程序升温溶剂热以及煅烧等不同方法制备了系列纳米复合材料Ag/ZnO,并采用X-射线衍射(XRD)、紫外-可见漫反射吸收光谱(UV-Vis/DRS)、X射线光电子能谱(XPS)、氮气吸附-脱附测定以及扫描电子显微镜配合X-射线能量色散谱仪(SEM-EDS)等测试手段对上述合成材料的晶型结构、形貌及表面物理化学性质进行了表征。结果表明,合成过程中辅以微波后其纤锌矿晶型结构未发生明显变化。但同时,其光的吸收性质以及粒子尺寸、形貌以及颗粒分布等方面则有较大改变。其中,经微波辐射、程序升温溶剂热以及煅烧三步处理的样品(mcd-Ag/ZnO)更多呈现规则的六棱柱结构。在紫外光照射和微波辐射下,合成产物光催化降解罗丹明B的实验结果显示,经微波辅助合成的Ag/ZnO光催化活性较未经微波处理样品的活性有较大提高,且明显高于市售P25。同时,mcd-Ag/ZnO在微波辐射下的光催化活性也被有效增强。     

Co掺杂ZnO纳米棒的水热法制备及其光致发光性能

以Zn(NO3)2·6H2O 和Co(NO3)2·6H2O为原料, 通过水热法在较低温度下制备了纯ZnO和Co掺杂的ZnO(ZnO:Co)纳米棒. 利用XRD、EDS、TEM和HRTEM对样品进行了表征, 结合光致发光(PL)谱研究了样品的PL性能. 结果表明, 水热法制备纯ZnO和ZnO:Co纳米棒均具有较好的结晶度. Co2+是以替代的形式进入ZnO晶格, 掺入量为2%(原子分数)左右. 纯的ZnO纳米棒平均直径约为20 nm, 平均长度约为180 nm; 掺杂样品的平均直径值约为15 nm, 平均长度约为200 nm左右; Co掺杂轻微地影响ZnO纳米棒的生长. 另外, Co掺杂能够调整ZnO纳米棒的能带结构、提高表面态含量, 进而使得ZnO:Co纳米棒的紫外发光峰位红移, 可见光发光能力增强.     

ZnO/SAPO-34组装体的制备及发光性质研究

以微孔分子筛SAPO-34为主体，采用锌盐浸渍-灼烧的方法，在SAPO-34的菱沸石笼中制备出ZnO纳米粒子，并对不同温度下灼烧后得到的ZnO/SAPO-34组装体的发光性质进行了研究。由于SAPO-34菱沸石笼的尺寸所限，制备出来的ZnO粒子粒径小于1 nm。量子尺寸效应使得SAPO-34笼中的ZnO纳米粒子的荧光光谱在近紫外区的发射谱峰有明显的蓝移。     

Speciation of zinc in nano phosphor particulars abstracted in an ionic liquid

Nano size (<100 nm) pollutants have been controlled negligibly in traditional air pollution control devices. Phosphor particulates escaped from filtration systems (bag houses or electrostatic precipitators) of used TVs, monitors or FEDs disassembling processes are frequently found in nano or submicron sizes. Experimentally, in a very short contact time (<2 min), more than 90% of the nano phosphor particulates could be abstracted into room temperature ionic liquid (RTIL) (e.g., [C₄min][PF₆]). The least-square fitted X-ray absorption near edge structural (XANES) spectra show that nano ZnS (88%) and ZnO (12%) could be suspended in the RTIL for at least 10 days.     

Luminescence properties of Cu-activated BaZnOS phosphor

Cu-activated BaZnOS was studied for the first time as a novel and efficient blue-emitting phosphor. Under the excitation of UV radiation, the phosphor can efficiently give a blue emission centered at 430 nm, corresponding to the transition from conduction band edge to the excited state of Cu²⁺ in the BaZnOS host. The maximum emission intensity occurs at 0.08 mol% of the Cu doping content for both photoluminescence (PL) and X-ray excited luminescence. The optimized blue-emitting BaZnOS:Cu phosphor has a larger PL intensity than the well-known green-emitting ZnO:Cu and blue-emitting ZnS:Cu phosphors. The excellent luminescence properties are tightly related to the appropriate direct band gap and the unique crystal structure of BaZnOS host. These results strongly indicate that the Cu-activated BaZnOS is a potential material used as a new high-brightness blue phosphor for UV light-emitting diode and display devices.