The structure and photoluminescence properties of ZnO nanobelts prepared by a thermal evaporation process

ZnO nanobelts had been synthesized by a simple method of thermal evaporation of Zn powders. The morphology, structure and photoluminescence (PL) properties of ZnO nanobelts were studied. The nanobelts had a single-crystal hexagonal structure and grew along the (0 0 0 1) direction with several micrometers long, 50-400 nm wide and 30-100 nm thick. Photoluminescence measurement showed that the nanobelts had an intensive near-band ultraviolet emission at about 3.3 eV. The obtained experimental data suggest that the ultraviolet PL in ZnO nanobelts originates from the recombination of the acceptor-bound excitons and free extions at room temperature. The absence of the deep level emission indicated very low impurity concentration and high crystalline quality in the ZnO nanobelts. Large-area growth and high quality indicate that the prepared ZnO nanobelts have potential application in optoelectronic devices.     

Structural,morphological, optical and antibacterial activity of rod-shaped zinc oxide and manganese-doped zinc oxide nanoparticles

Pure ZnO and Mn-doped ZnO nanoparticles were synthesized by Co-precipitate method. The structural characterizations of the nanoparticles were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. UV–Vis, FTIR and photoluminescence (PL) spectroscopy were used for analysing the optical properties of the nanoparticles. XRD results revealed the formation of ZnO and Mn-doped ZnO nanoparticles with wurtzite crystal structure having average crystalline size of 39 and 20 nm. From UV–Vis studies, the optical band-gap energy of 3.20 and 3.25 eV was obtained for ZnO and Mn-doped ZnO nanoparticles, respectively. FTIR spectra confirm the presence of ZnO and Mn-doped ZnO nanoparticles. Photoluminescence analysis of all samples showed four main emission bands: a strong UV emission band, a weak blue band, a weak blue–green band and a weak green band indicating their high structural and optical qualities. The antibacterial efficiency of ZnO and Mn-doped ZnO nanoparticles were studied using disc diffusion method. The Mn-doped ZnO nanoparticles show better antibacterial activity when higher doping level is 10 at% and has longer duration of time.     

Atomic layer deposition coating of ZnO shell for GaN-ZnO core-sheath heteronanowires

We have synthesized GaN-core/ZnO-shell nanowires and investigated effects of the ZnO coating. The X-ray diffraction pattern showed that as-synthesized samples are composed of GaN and ZnO. Transmission electron microscopy indicated that the deposited ZnO shell layer is poly-crystalline. The photoluminescence (PL) spectrum of GaN has been changed by the ZnO coating, where emission bands centered at roughly 1.9 eV, 2.5 eV, and 3.3 eV were newly added to the emissions from core GaN nanowires. We found that overall PL intensity has been significantly increased by coating the ZnO shell layers.     

Spectral behavior of the emission around 3.31 eV (A-line) from ZnO nanocrystals

The emission at around 3.31 eV (A-line) from three types of ZnO nanocrystals with different particle sizes (10-1000 nm) was studied. The photoluminescence (PL) measurements were performed under different excitation densities and at different temperatures. The A-line emission exhibited a strong dependence on temperature and excitation power density. With increasing excitation density and temperature overlapping of the closely spaced first longitudinal optical (LO) phonon replica of free excitons by the A-line emission was observed.     

纳米ZnO薄膜的激子光致发光特性

报道了纳米ZnO薄膜激子光致发光(PL)与温度的关系。首先利用低压金属有机化学气相沉积(LPMOCVD)技术生长ZnS薄膜,然后将ZnS薄膜在氧气中于800℃下热氧化2h获得纳米ZnO薄膜。X射线衍射(XRD)结果表明,纳米ZnO薄膜具有六角纤锌矿多晶结构且具有择优(002)取向。室温下观察到一束强的紫外(326eV)光致发光(PL)和很弱的深能级(DL)发射。根据激子峰的半高宽(FWHM)与温度的关系,确定了激子纵向光学声子(LO)的耦合强度(ГLO)。     

掺AlZnO纳米线阵列的光致发光特性研究

采用化学气相沉积方法，以金做催化剂，在Si (100)衬底上制备了掺AlZnO纳米线阵列.扫描电子显微镜(SEM)表征发现ZnO纳米线的直径在30nm左右.X射线衍射(XRD)图谱上只存在ZnO的(002)衍射峰，说明ZnO纳米线沿c轴择优取向.掺AlZnO纳米线阵列的室温光致发光(PL)谱中出现了3个带边激子发射峰：373nm，375nm，389nm.运用激子理论推算出掺AlZnO纳米线的禁带宽度为3.343eV ，束缚激子结合能为0.156eV；纯ZnO纳米线阵列PL谱中3个带边激子发射 关键词： 光致发光 化学气相沉积(CVD) 激子 ZnO纳米线阵列     

液相激光烧蚀合成ZnO及Zn/ZnO纳米颗粒及其光致发光性能

利用532 nm脉冲激光对沉浸在去离子水及十二烷基硫酸钠(SDS)水溶液中的金属锌靶进行液相激光烧蚀,合成了ZnO纳米颗粒和Zn/ZnO核壳结构的纳米粒子. 应用X射线衍射仪,透射电子显微镜,紫外可见光分光光度计和荧光光度计表征产物的微观结构和光学性能,并探讨其形成机理. 结果表明:在去离子水中分别烧蚀2 h和4 h生成的ZnO纳米粒子的平均粒径分别为43 nm和19 nm. 激光的长时间作用可以使纳米粒子粒径减小. 在0.005 mol/L的SDS水溶液中合成了Zn/ZnO核壳结构的纳米粒子,这是由于S 关键词： 脉冲激光烧蚀 ZnO纳米粒子 核壳结构 光致发光     

Synthesis and characterization of ZnO nanoparticles using polyethylene glycol (PEG)

ZnO nanoparticles and ZnO encapsulated with polyethylene glycol (PEG) was synthesized using zinc acetate as a precursor at low temperature and characterized by different techniques. The influence of the types of solvent, synthesis parameters, and PEG encapsulation on the crystallization, the surface morphology, and the luminescent properties of ZnO nanoparticles prepared by the sol–gel process were investigated. The influence of different addition molar masses of the PEG during the synthesis on the ZnO emission peaks was systematically monitored. The crystallinity, the surface morphology, and the photoluminescence (PL) properties of ZnO depended highly on the synthesis process and PEG encapsulation. X-ray diffraction (XRD) spectra of ZnO nanoparticles show that all the peaks corresponding to the various planes of wurtzite ZnO indicate the formation of a single phase. The absorption edges of these ZnO nanoparticles are shifted by additions of the PEG polymer. The photoluminescence (PL) characterization of the ZnO nanostructures exhibited a broad emission in the visible range with maximum peak at 450 and/or 560 nm.     

Reversible quenching of luminescence in ZnO films by electric field action

We report the effect of the external electric field on the photoluminescence (PL) properties of ZnO films grown by a pulsed laser deposition method. The PL quenching of bound excitons under the electric field was attributed to a decrease in the capture cross section of the radiative centers. In addition, the change in the surface/grain boundaries charge induced a degradation of the 3.33 eV emission line over the whole sample, which remained even after voltage removal. Besides the PL degradation, this emission at 3.33 eV demonstrates the change in the thermal quenching process, where the activation energy of exciton detachment corresponds to its binding energy. All behaviors were restored to the initial state by application of the voltage with opposite polarity. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Optical and structural properties of MgZnO/ZnO hetero- and double heterostructures grown by pulsed laser deposition

MgZnO thin films, MgZnO/ZnO heterostructures (HS) and double heterostructures (DHS) have been prepared on a-plane sapphire substrates by means of pulsed laser deposition (PLD). A linear blueshift of the MgZnO emission with increasing Mg content is observed in photoluminescence spectroscopy (PL) at 2 K. Cathodoluminescence measurements verify the spatial homogeneity of the emission properties of the MgZnO films. The film roughness is evaluated from atomic force microscopy scans. In MgZnO/ZnO HS the ZnO grows on all appearing MgZnO facets. PL investigations of such PLD-grown heterostructures show the high optical quality of thin ZnO films (d≤100 nm) grown on MgZnO. Capping those structures with a thin MgZnO layer further improves their luminescence intensity and enhances the emission of free-exciton luminescence from the ZnO layers. MgZnO/ZnO/MgZnO DHS with nominal ZnO layer thicknesses of d_nom≤6 nm show a clear intensification of the ZnO PL. Temperature dependent PL and transmission measurements between 4.4 and 300 K prove the dominating emission to be due to the recombination of excitons localized in the ZnO. At 2 K, due to confinement effects, their emission energy is blueshifted up to 51 meV compared to free excitons in bulk ZnO. PACS 81.15.Fg; 78.66.Hf; 68.37.Ps     

Ex situ synthesis and optical properties of ZnO-PbS nanocomposites

Zinc oxide (ZnO) and lead sulphide (PbS) nanoparticles separately synthesized by a precipitation method were combined by an ex situ route to prepare ZnO-PbS nanocomposites with different molar ratios of ZnO and PbS. The structure and morphology of the ZnO, PbS and ZnO-PbS samples were analyzed with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). A UV-vis spectrophotometer was used to collect the absorption and 325 nm He-Cd and 488 nm Ar lasers were used to collect the photoluminescence data from the samples. ZnO nanoparticles showed a broad and stable emission peak at ∼570 nm, while a strongly quantum confined emission from PbS nanoparticles was detected at ∼1344-1486 nm. The ZnO-PbS nanocomposites exhibited dual emission in the visible and near-infrared (NIR) regions that is associated with defects and recombination of excitonic centres in the ZnO and PbS nanoparticles, respectively. The PL intensity of the visible emission from the ZnO-PbS nanocomposite was shown to increase when the ZnO to PbS molar ratio was 5:1 and the emission was almost quenched at molar ratios of 1:1 and 1:5. For different molar ratios of ZnO to PbS, the PL intensity of the NIR emission from the ZnO-PbS nanocomposites was more intense than that of PbS nanoparticles.     

Characterization of ZnO:Co particles prepared by hydrothermal method for room temperature magnetism

ZnO based diluted magnetic semiconductor particles (ZnO:Co) have been grown using a hydrothermal method with good crystallinity. The atomic percentage of Co presented in the specimen is about 0.01. Based on the x-ray diffraction and high-resolution transition electron, Co is found to be incorporated into ZnO lattice without evidence of obvious Co precipitates. However, from photoluminescence (PL) spectra in the range of 1.94 -3.45 eV, a strong broad emission centered around 600 nm (2.07 eV) in the visible range as well as a relatively weak peak at 2.81 eV are observed, indicating the presence of Co impurities. Moreover, intrinsic emissions such as D^OX suggest that at least some Co have been doped into ZnO lattice, substituting for Zn²⁺ ions. The PL results further confirm the substitution of Zn²⁺ ions by Co, which leads to the changes of the electronic band structures. Magnetism could be realized at room temperature for the ZnO:Co nanoparticles under our experimental conditions although with low coercivity. The field-cooled and zero-field-cooled curves can be explained as a result of competition between the ferromagnetic and the antiferromagnetic ordering in the ZnO:Co nanoparticles. Combining the results from PL and magnetism characterization, it is reasonable to think that both doped Co in the ZnO lattice and Co impurities contribute to magnetism in ZnO:Co nanoparticles at room temperature.     

水热合成ZnO:Cd纳米棒的微结构及光致发光特性

采用水热法制备了ZnO和不同掺杂浓度的ZnO:Cd纳米棒,通过SEM,XRD、拉曼光谱等的分析,研究了ZnO和ZnO:Cd的微结构并测试分析了其光致发光特性.结果表明,ZnO和ZnO:Cd纳米棒呈六角纤锌矿结构,Cd掺杂使得纳米棒体积更小.由于内部张应力的影响,Cd掺杂使得材料光学带隙减少.当掺杂浓度为2%时,合成的材料光致发光谱中出现了位于2.67 eV处,由导带底和Zn空位(VZn)缺陷能级跃迁造成的蓝光发射峰,并且Cd的掺入使得位于2.90 eV附近的紫光发射峰强度增强,对于研究ZnO蓝紫发光器件具有重要的意义.     

Fine structure on the excitonic emission in AgI nanoparticles embedded in silica glass

Stable photoluminescence (PL) from AgI nanoparticles embedded in silica glass was investigated at room temperature. The Z_1,2 excitonic emission of AgI exhibits fine structure with spacing of ∼0.20 eV (1610 cm⁻¹), which is assigned to the frequency of vibration in interfacial water species. The PL excitation spectrum displays two newly observed bands at 3.45 and 4.35 eV associated with AgI-silica interaction. We suggest that the excitons in AgI are localized in the AgI/SiO₂ interface region before radiative recombination.     

Photoluminescence and time-resolved photoluminescence of star-shaped ZnO nanostructures

Optical properties of star-shaped ZnO nanostructures were studied. The temperature-dependent photoluminescence (PL) was examined up to fourth-order longitudinal optical (LO) phonon assisted emissions of free excitons and confirmed that the nature of the room temperature PL in ZnO is 1-LO phonon assisted emission of free excitons. Low threshold ultraviolet stimulated emissions (SE) were obtained for our powder samples at room temperature. Picosecond time-resolved PL measurements detected a bi-exponential decay behavior which is strongly dependent on the excitation intensity: the slow decay term decreased faster than the fast decay term as the excitation intensity increased and the emission decays were dominated by the fast one. We also found that the emission decays decreased super-linearly before the appearance of the SE. This behavior may be used to deduce the threshold of SE or lasing.     

Synthesis and optical properties of N-In codoped ZnO nanobelts

N-In codoped ZnO nanobelts were successfully synthesized via high-temperature chemical vapor deposition for the first time, using the mixture of In/ZnO as a precursor. The EDX spectrum showed that In was introduced into ZnO nanobelts. In order to better understand the optical properties of N-In codoped ZnO nanobelts, the Raman and low-temperature PL spectra of the undoped, In-doped and N-In codoped ZnO nanostructures were measured. By contrasting, N is incorporated into the nanobelts. The temperature dependent photoluminescence (PL) spectra were investigated. Their PL spectra in the temperature from 9 K to room temperature were dominated by an A^oX emission of excitons bound to 2No-In_Zn acceptor complexes. The dissociation energy of the acceptor complexes is estimated to be 89-112 meV.     

Hydrogen passivation effect on the yellow-green emission band and bound exciton in n - ZnO

Photoluminescence (PL) measurements performed on as-grown, hydrogenated, and annealed n-type ZnO bulk samples investigated the origins of their yellow (2.10 eV) and green (2.43 eV) emission bands. After hydrogenation, the defect-related peak at 2.10 eV was no longer present in the room temperature PL spectrum, the peak intensity at 2.43 eV was unchanged, and the intensity of the emission peak at 3.27 eV increased significantly. These results indicate that yellow band emission is due to oxygen vacancies, as the emission peak at 2.10 eV disappears when hydrogen atoms passivate these vacancies. The emission peak at 2.43 eV originates from complexes between oxygen vacancies and other crystal defects. We discuss the shallow donor impurities arising due to these hydrogen atoms in the ZnO bulk sample.     

New phenomenon in the channels of mesoporous silicate CMI-1: quantum size effect and two-photon absorption of ZnO nanoparticles

Quantum size effect (QSE) and very efficient laser action were observed in ZnO-mesoporous CMI-1 silica nanocomposites prepared through the incorporation of ZnO nanoparticles inside the channels of a silica mesoporous material CMI-1. The incorporation was made by direct impregnation of the mesoporous material in a zinc nitrate aqueous solution followed by calcination. The PL spectrum of the nanocomposites presents a significant blue-shift corresponding to the enhancement of the semiconductor band gap. Being excited by incident photons with energy of 1.82 eV, the ZnO nanoparticles exhibit spontaneous emission due to the excitonic recombination. In our samples, spontaneous emission turns to stimulated emission when the pumping intensity reaches a threshold value. This effect implies a two-photon excitation which was never observed with ZnO nanoparticles. This paper deals with results about the characteristics of the matrix and the nanocomposites and the lasing effect. A two-photon excitation phenomenon has been observed. PACS 81.05.Zx; 78.45.+h; 78.55.-m; 78.30.Fs; 72.80.Tm; 61.43.Gt; 61.46.+w; 61.66.Fn     

Effect of barium doping on the physical properties of zinc oxide nanoparticles elaborated via sonochemical synthesis method

The aim of this work is to study the effect of barium (Ba) doping on the optical, morphological and structural properties of ZnO nanoparticles. Undoped and Ba-doped ZnO have been successfully synthesized via sonochemical method using zinc nitrate, hexamethylenetetramine (HMT) and barium chloride as starting materials. The structural characterization by XRD and FTIR shows that ZnO nanoparticles are polycrystalline with a standard hexagonal ZnO wurtzite crystal structure. Decrease in lattice parameters from diffraction data shows the presence of Ba²⁺ in the ZnO crystal lattice. The morphology of the ZnO nanoparticles has been determined by scanning electron microscopy (SEM). Incorporation of Ba was confirmed from the elemental analysis using EDX. Optical analysis depicted that all samples exhibit an average optical transparency over 80%, in the visible range. Room-temperature photoluminescence (PL) spectra detected a strong ultraviolet emission at 330 nm and two weak emission bands were observed near 417 and 560 nm. Raman spectroscopy analysis of Ba-doped samples reveals the successful doping of Ba ions in the host ZnO.     

氢化后ZnO发光性质的变化

通过低温光致发光(PL)谱研究氢化对ZnO发光性质的影响。氢通过一个直流等离子体发生装置引入到ZnO晶体。研究发现氢的引入影响了束缚激子的相对发光强度,特别是I4峰(3.363eV)的强度增加和3.366eV峰出现。比较未氢化样品,氢化样品PL谱显示不同的温度依赖。