Effect of Mn doping on the microstructures and photoluminescence properties of CBD derived ZnO nanorods

Mn-doped ZnO nanorods were synthesized from aqueous solutions of zinc nitrate hexahydrate, manganese nitrate and methenamine by the chemical solution deposition method (CBD). Their microstructures, morphologies and optical properties were studied in detail. X-ray diffraction (XRD) results illustrated that all the diffraction peaks can be indexed to ZnO with the hexagonal wurtzite structure. Scanning electron microscope (SEM) results showed that the average diameter of Mn-doped ZnO nanorods was larger than that of the undoped one. Photoluminescence (PL) spectra indicated that manganese doping suppressed the emission intensity and caused the blue shift of UV emission position compared with the undoped ZnO nanorods. In the Raman spectrum of Mn-doped ZnO nanorods, an additional mode at about 525 cm⁻¹ appeared which was significantly enhanced and broadened with the increase of Mn doping concentration.     

Enhanced photocatalytic activity of Cu-doped ZnO nanorods

Cu-doped ZnO nanorods with different Cu concentrations were synthesized through the vapor transport method. The synthesized nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–vis spectroscopy. The XRD results revealed that Cu was successfully doped into ZnO lattice. The FE-SEM images showed that the undoped ZnO has needle like morphology whereas Cu-doped ZnO samples have rod like morphology with an average diameter and length of 60–90 nm and 1.5–3 μm respectively. The red shift in band edge absorption peak in UV-vis absorbance spectrum with increasing Cu content also confirm the doping of Cu in ZnO nanorods. The photocatalytic activity of pure and Cu-doped ZnO samples was studied by the photodegradation of resazurin (Rz) dye. Both pure ZnO and the Cu-doped ZnO nanorods effectively removed the Rz in a short time. This photodegradation of Rz followed the pseudo-first-order reaction kinetics. ZnO nanorods with increasing Cu doping exhibit enhanced photocatalytic activity. The pseudo-first-order reaction rate constant for 15 % Cu-doped ZnO is equal to 10.17×10^?2min^?1 about double of that with pure ZnO. The increased photocatalytic activity of Cu-doped ZnO is attributed to intrinsic oxygen vacancies due to high surface to volume ratio in nanorods and extrinsic defect due to Cu doping.     

Ga掺杂对ZnO纳米结构可见光发射的抑制效应

采用碳热还原反应和原位掺杂的方法制备了不同Ga掺杂浓度的ZnO纳米结构. X射线衍射 显示掺杂纳米结构中为单一的氧化锌纤锌矿结构. 扫描电子显微镜 观测发现随掺杂浓度的增大, 纳米结构的形貌逐渐从纳米六棱柱变为纳米锥.光致发光 和X射线光电子能谱 测量分别发现随着掺杂浓度升高, 纳米结构的可见发光强度和其中空位 氧峰相对强度逐渐减小直至消失, 两者存在很强的相关性. 上述结果为ZnO可见光发射的氧空位机理提供了新的实验证据. 对Ga掺杂抑制纳米结构中氧空位的原因进行了分析.     

Structural, morphological and photoluminescence properties of W-doped ZnO nanostructures

W-doped ZnO nanostructures were synthesized at substrate temperature of 600 °C by pulsed laser deposition (PLD), from different wt% of WO₃ and ZnO mixed together. The resulting nanostructures have been characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and photoluminescence for structural, surface morphology and optical properties as function of W-doping. XRD results show that the films have preferred orientation along a c-axis (0 0 L) plane. We have observed nanorods on all samples, except that W-doped samples show perfectly aligned nanorods. The nanorods exhibit near-band-edge (NBE) ultraviolet (UV) and violet emissions with strong deep-level blue emissions and green emissions at room temperature.     

Fabrication and characterization of ZnO and ZnMgO nanostructures grown using a ZnO/ZnMgO compound as the source material

ZnO and ZnMgO nanostructures were synthesized on Si (1 0 0) substrates with the assistance of a gold catalyst, using a thermal evaporation method with a ZnO/ZnMgO compound as the source material. The substrates were placed in different temperature zones. ZnO nanostructures with different morphologies and different compounds were obtained at different substrate temperatures. Nanostructures with nanorods and nanosheets morphologies formed in the low and high temperature zones, respectively. The nanorods grown in the low temperature zone had two phases, hexagonal and cubic. Energy dispersive X-ray (EDX) results showed that the nanorods with a cubic shape contained more Mg in comparison to the nanowires with a hexagonal shape. We found that the substrate temperature and the gold catalyst were two key factors for the doping of Mg and the formation of nanostructures with different morphologies. Room temperature photoluminescence spectroscopy showed a blue-shift for the nanostructures with the nanorods morphology. This shift could be attributed to Mg effects that were detected in the nanorods.     

Synthesis,characterization and photoluminescence of ZnO:Cd rosette-like nanostructures using solution process

Well crystalline undoped and Cd-doped ZnO rosette-like structures were successfully synthesized at low temperature (80 °C) via solution process technique during 30 min. Zinc nitrate, cadmium nitrate, sodium hydroxide and hexamine were used as starting materials. The morphology and microstructure were determined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. X-ray diffraction indicated that the structure has a single phase with wurtzite structure. FESEM indicated that rosette like structures have been formed. This rosette consists of nanorods with length 210 and 460 nm and diameter 50 and 74 nm for undoped and Cd doped ZnO, respectively. HRTEM showed a decrease in the lattice parameter after the Cd doping. EDX showed that the amount of Cd incorporated into ZnO is 6.4 wt.%. Photoluminescence measurements taken on both doped and undoped samples showed that, in the Cd-doped ZnO nanostructures, the band-edge UV emission is blue shifted and the broad green emission intensity decreased.     

Temperature-dependent growth mode of W-doped ZnO nanostructures

We report on the effects of glass substrate temperature on the crystal structure and morphology of tungsten (W)-doped ZnO nanostructures synthesized by pulsed-laser deposition. X-ray diffraction analysis data shows that the W-doped ZnO thin films exhibit a strongly preferred orientation along a c-axis (0 0 0 L) plane, while scanning electron and atomic force microscopes reveal that well-aligned W-doped ZnO nanorods with unique shape were directly and successfully synthesized at substrate temperature of 550 °C and 600 °C without any underlying catalyst or template. Possible growth mechanism of these nanorods is suggested and discussed.     

Improvement of ZnO nanorod based quantum Dot (cadmium sulfide) sensitized solar cell efficiency by aluminum doping

This study investigates the performance of quantum dot sensitized solar cells (QDSSCs) based on aluminum (Al)-doped and undoped ZnO nanorods. Current density–voltage (J–V) characterization shows that Al doping into ZnO nanorods (AZO NRs) can improve short circuit current density (J_sc) and the energy conversion efficiency (η) of QDSSCs. The maximum η=1.15% is achieved in QDSSCs when Al concentration is 0.5 wt%, as compared to undoped state where η=0.57%. These current densities and the energy conversion efficiency improvement are studied using the electrochemical impedance spectroscopy (EIS). EIS results indicate that the electron transport resistance in the photoanode of QDSCs is reduced with introduction of Al into ZnO structure, which leads to increasing J_sc. It is also found that recombination resistance reduces with introduction of Al into ZnO because of the upward displacement of Fermi level with respect to AZO conduction band (CB) and increasing electron density in the ZnO CB. This reduction of recombination resistance causes higher recombination rate in QDSCs based AZO NRs.     

Investigation of Cu Doping,Morphology and Annealing Effects on Structural and Optical Properties of ZnO:Dy Nanostructures

Dysprosium (Dy) doped ZnO nanosheets and nanorods were synthesized by hydrothermal method. Effects of Cu doping, morphology and annealing in Oxygen ambient on structural and optical properties of ZnO nanostructures were investigated using X–ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectra (DRS) and photoluminescence (PL) spectroscopy. This study recommends that both of intrinsic and extrinsic defects facilitate energy transfer (ET) from the ZnO host to Dy³⁺ ions and consequently have an effective role on producing intense Dy emissions at indirect excitation. The results also revealed that annealing process improved the crystal structure of ZnO nanorods due to decrease of surface; however decreased ET and Dy emissions because of diminishing in oxygen vacancy. In addition, as a result of increasing of surface area in nanorods compared to nanosheets, the oxygen vacancies and ET were enhanced. Moreover the results exhibited that electrical and optical properties of ZnO:Dy can be tuned by various amount of Dy concentrations and also Cu doping.     

Fabrication of ZnO nanostructures of various dimensions using patterned substrates

ZnO nanostructures were grown on silicon, porous silicon, ZnO/Si and AlN/Si substrates by low-temperature aqueous synthesis method. The shape of nanostructures greatly depends on the underlying surface. Scattered ZnO nanorods were observed on silicon substrate, whereas aligned ZnO nanowires were obtained by introducing sputtered ZnO film as a seed layer. Furthermore, both the combination of nanorods and the bunch of nanowires were found on porous silicon substrates, whereas platelet-like morphology was observed on AlN/Si substrates. XRD patterns suggest the crystalline nature of aqueous-grown ZnO nanostructures and high-resolution transmission electron microscopy images confirm the single-crystalline growth of the ZnO nanorods along [0 0 1] direction. Room-temperature photoluminescence characterization clearly shows a band-edge luminescence along with a visible luminescence in the yellow spectral range.