Controlled growth and properties of Pb doped ZnO nanodisks

Pb²⁺ doped zinc oxide nanodisks have been grown through a facile solvothermal method. The nanodisks have perfect hexagonal shape with about 1 μm in diagonal and 100 nm in thickness. The existence of Pb²⁺ is vital to the formation of the disk morphology. Room temperature photoluminescence measurements show two photoluminescence peaks centered at 518 and 648 nm. The mechanism of the nanodisk growth is also discussed.     

分级微纳结构氧化锌的制备及其光致发光

采用低温热蒸发法研制出新型的ZnO分级微纳结构,利用场发射扫描电子显微镜和X射线衍射仪对其形貌与结构进行了表征,结果表明,所制备的分级结构为纯六方纤锌矿结构,由主干直径为1-3μm的ZnO微米线和表面的宽度为1μm、厚度约为100nm的晶片组成。用气-固（VS）机制阐明了ZnO分级结构的生长机理。在室温下,用近场光学显微镜测量了ZnO分级结构的光致发光谱,结果显示,在380nm处存在很强的近带隙发光峰,而508nm左右的缺陷发光很弱。     

Preparation of monodisperse ZnO/SiO2 composite particles using spray drying with an anionic surfactant template and their photoluminescence characteristics

The photoluminescence (PL) characteristics of ZnO/SiO₂ composite particles were investigated. ZnO/SiO₂ composite particles were synthesized utilizing the consecutive sol–gel spray drying method by incorporating sodium lauryl sulfate (SLS) as a particle morphology control agent. The effect of SLS concentration and ZnO ratio on precursors was studied further on the composite particle morphology and PL performance. Elevating the SLS concentration exhibited a reduction in the particle diameter and an increase in particle uniformity. The particle diameter without SLS was 6.18 µm and reduced to 2.6 µm with the addition of SLS at 3 critical micelle concentrations (CMC). The decrease in ZnO concentration also reduced the particle diameter of the ZnO/SiO₂ composite to 1.74 µm at a ZnO concentration of 25% mol. In addition, the increase in the excitation wavelength from 230 nm to 320 nm indicates a shift in the peak emission intensity at higher wavelengths from 467 nm to 645 nm. The excitation wavelength-dependent photoluminescence phenomenon was exhibited by incorporating silica into the ZnO precursor pre- and post-drying to deliver composite particles. The addition of silica to the composite particles can augment the PL emission intensity without causing a shift in the PL emission peaks when excited at the same wavelength. The 25% mol ZnO composite particles with the addition of SLS 3 CMC had the highest PL emission intensity. The amount of silica nanoparticles sufficient to trap the ZnO nanoparticles in the droplet is an important factor besides the size and uniformity of the particles, which causes the high intensity of PL emission.     

Synthesis of violet light emitting single crystalline ZnO nanorods by using CTAB-assisted hydrothermal method

ZnO nanorods were grown by cetyl trimethylammonium bromide assisted hydrothermal technique from a single molecular precursor. The phase and structural analysis were carried out by X-ray diffraction technique and Raman spectroscopy, respectively. The phase and structural analysis has suggested that as prepared nanorods have hexagonal wurzite structure. Morphology of the nanorods was investigated by electron microscopy techniques which showed the formation of well dispersed nanorods of 100 ± 10 nm in diameter and 900 ± 100 nm in length. Optical properties were investigated by photoluminescence spectroscopy. As prepared ZnO nanorods have shown intense room temperature photoluminescence peak in the violet region at 403 nm. Absence of defect mediated green luminescence peak suggests the formation of well crystalline ZnO nanorods without any impurities or structural defects.     

Structure and photoluminescence of S-doped ZnO nanorod arrays

Vertically aligned S-doped ZnO nanorod arrays have been successfully synthesized by hydrothermal method at 90 °C for 2 h. The obtained nanorod is ～ 70 nm in diameter and 1.2 μm in length. The XRD pattern and the Raman spectra indicate that the S-doped nanorod arrays are orientated at [001] and are single crystals with hexagonal wurtzite structure. The photoluminescence (PL) spectra show that S-doped ZnO nanorod arrays exhibit a relative weak ultraviolet (UV) emission, a violet emission and a strong green emission. The effects of S-doping on the structure and photoluminescence of ZnO nanorod arrays are discussed in detail.     

The role of ammonia hydroxide in the formation of ZnO hexagonal nanodisks using sol–gel technique and their photocatalytic study

ZnO nanomaterials with large surface area are desired particularly for the gas sensor, biosensor and photocatalyst applications. In this study, ZnO hexagonal nanodisks with thickness to diagonal aspect ratio (～1/80) were successfully synthesised via sol–gel approach. By using aluminium sulphate as a complexing agent and carefully controlling the amount of ammonia hydroxide, zinc oxide hexagonal nanodisks were produced. The ZnO nanodisks had perfect hexagonal shape with about 4 μm in diagonal and 50 nm in thickness. The growth of the nanodisks was favoured along the six symmetric directions of ±[1ī00], ±[01ī0] and ±[10ī0]. The growth mechanism of ZnO hexagonal nanodisks is proposed as follows. The formation of ZnO hexagonal nanodisks was mediated by the adsorption of aluminate ions, Al(OH)₄^?, on the polar surface of ZnO. The Al(OH)₄^? ions were produced as a result of reaction between Al₂(SO₄)₃ and NH₄OH. The Al(OH)₄^? ions were bonded to the positively charged Zn²⁺-terminated (0001) polar surface of ZnO. This suppressed the preferential growth of ZnO along [0001] direction but allowed the lateral growth of ZnO in <01ī0>. Eventually, ZnO hexagonal nanodisks with ±(0001) top/bottom surfaces and {1ī00} side surfaces were formed. The size of the ZnO hexagonal nanodisks could be adjusted via the synthesis duration and the amount of ammonia hydroxide. The photocatalytic study indicates that ZnO hexagonal nanodisks were a good photocatalyst for the degradation of Rhodamine B under ultraviolet light irradiation with a rate constant of 0.036 min^?1.     

Simple air oxidation synthesis and optical properties of S-doped ZnO microspheres

The S-doped ZnO microspheres with average diameter of 3 micrometers (μm) have been successfully synthesized by a simple air oxidation process of ZnS precursor. X-ray diffractometer (XRD) pattern indicates that the as-obtained sample is composed of ZnO and ZnS. The scanning electron microscopy (SEM) image shows that the exterior surfaces of the microspheres are composed of many nanoparticles with an average grain size of 100 nanometers (nm). The photoluminescence (PL) spectra show the broad excitation region with the main peak at 370 nm and strong green emission centered at 500 nm, which can be attributed to the oxygen vacancies caused by S replacement of O.     

Synthesis of highly luminescent CdTe/ZnO core/shell quantum dots in aqueous solution

The synthesis and photoluminescence (PL) properties of aqueous CdTe/ZnO core/shell quantum dots (QDs) have been investigated by using thiolglycolic acid as a capping reagent. The highlighted contribution of the present study was CdTe QDs coated with a ZnO shell by controlling the hydrolysis process of Zn(OAc)₂. The QDs benefitted from overcoming the high lattice mismatch between CdTe and ZnO. The PL peak wavelength of the CdTe/ZnO QDs with high PL quantum yields up to 88% was located in a range between 547 and 596 nm by adjusting the size of CdTe cores and the thickness of ZnO shells. The results of X-ray diffraction analysis and transmission electron microscopy observation indicate that the dot-shaped CdTe/ZnO QDs (566 nm) with an average size of 2.2 nm in diameter belong to the cubic CdTe crystal structure. Due to the passivation of surface defects, it is found that the luminescence decay curves accord with a biexponential decay model of exciton and trap radiation behavior. The average PL lifetimes of CdTe (571 nm) and CdTe/ZnO (596 nm) QDs at room temperature are 27.3 and 35.1 ns, respectively.     

Effects of processing parameters on ultraviolet emission of In-doped ZnO nanodisks grown by carbothermal reduction

Effects of cooling rate and oxygen partial pressure in flowing Ar on ultraviolet (UV) emission of In-doped ZnO nanodisks grown by carbothermal reduction at 1000 °C were studied. The In doping favored the growth of ZnO nanodisks instead of ZnO nanowires. Air-cooled ZnO nanodisks showed a strong green emission, while furnace cooling in conjunction with introducing O₂, around 1.0%, into flowing Ar during growth significantly enhanced the growth and UV emission of ZnO nanodisks. The causes can be attributed to the reduction of oxygen vacancies and surface defects in ZnO nanodisks. However, higher oxygen partial pressure in flowing Ar resulted in a decrease in the Zn vapor and thus suppressed the growth and UV emission of ZnO nanodisks.     

Strong yellow emission of ZnO hollow nanospheres fabricated using polystyrene spheres as templates

ZnO hollow nanospheres were fabricated using polystyrene (PS) microspheres as templates were demonstrated in this paper. The structures and morphologies of obtained products were characterized by XRD, FESEM and TEM. The results revealed that ZnO hollow nanospheres possess a hexagonal wurtzite structure with a diameter around 450–500 nm. Ultraviolet–visible (UV–vis) analysis showed that ZnO hollow nanospheres had high absorption in the ultraviolet region and low absorption in the visible region. Room temperature photoluminescence (PL) spectrum showed a weak UV emission at 380 nm and a strong and broad yellow emission centered at 550 nm. The formation mechanism of hollow structure was also investigated.     

Photo-initiated growth of zinc oxide (ZnO) nanorods

A photo-initiated process via femtosecond pulse-induced heterogeneous nucleation in zinc ammine complex (Zn(NH₃)₄²⁺)-based aqueous solution without catalyst and surfactant, followed by hydrothermal treatments for crystal growth into zinc oxide (ZnO) nanorods, was investigated. Flat-top hexagonal ZnO nanorods with smooth planes of diameter ≥ 100 nm and length ≤ 1 μm were grown with laser irradiation, compared to porous rod-like structures without irradiation. The flat-top planes indicate slow growth rate, due to the intermediate step of Zn(NH₃)₄²⁺ decomposition to Zn(OH)₄²⁻, before dehydration to ZnO. Prolonged hydrothermal treatment produced nanotubes and lateral splits due to OH⁻ erosion of the crystal faces. XRD analysis showed a hexagonal crystal structure while photoluminescence study indicated a peak at about 380 nm.     

Morphology and time resolved photoluminescence of electrochemically synthesized zinc oxide nanowires

The paper presents the synthesis of ZnO nanowires (~100 nm) from aqueous solution at relatively lower temperature (~70 °C) by cathodic electrodeposition using anodic alumina membrane (AAM). The nanowires were characterized by scanning electron microscopy, X-ray diffraction and photoluminescence. Strong reflections corresponding to (100), (002), (101), (102) and (110) indicate the Wurtzite structure of synthesized ZnO nanowires. Room temperature time resolved photoluminescence study shows the visible emission at 590 nm (2.1 eV) which is attributed to deep level emission on account of defects. Time resolved photoluminescence studies are very important, if we want to use these ZnO nanowires for any optoelectronic application.     

Size and defect related broadening of photoluminescence spectra in ZnO:Si nanocomposite films

Nanocomposite films of zinc oxide and silicon were grown by thermal evaporation technique using varying ratios of ZnO:Si in the starting material. Structural analyses reveal the role of ZnO and amorphous silicon interface in contributing to the relatively less common blue photoluminescence emissions (at ～410 and 470 nm). These blue peaks are observed along with the emissions resulting from band edge transition (370 nm) and those related to defects (520 nm) of ZnO. Careful analysis shows that along with the grain size of ZnO, a suitable compositional ratio of ZnO to silicon is critical for the coexistence of all the four peaks. Proper selection of conditions can give comparable photoluminescence peak intensities leading to broad-band emission.     

Vanadium oxide nanodisks: Synthesis,characterization, and electrochemical properties

Highly crystallined VO_1.6·H₂O nanodisks assembled from nanoparticles have been successfully fabricated under hydrothermal conditions by using bulk V₂O₅ and Na₂S₂O₃ as the starting materials in the presence of surfactant polyethylene glycol 4000 (PEG-4000). The nanodisks have a diameter of 200 nm and thickness of 40 nm. Hollow nanodisks are occasionally observed, which is similar to Chinese ancient copper coins. The formation of nanodisks can be ascribed to a novel solid-solution-solid growth mechanism. Compared with other methods, the solid state transformation method is simple and economic. In addition, the nanodisks exhibit good electrochemical behavior and promising to be used in lithium-ion battery.     

Growth and optical and field emission properties of flower-like ZnO nanostructures with hexagonal crown

Flower-like zinc oxide (ZnO) nanostructures with hexagonal crown were synthesized on a Si substrate by direct thermal evaporation of zinc power at a low temperature of 600 °C and atmospheric pressure. Field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy and photoluminescence were applied to study the structural characteristics and optical properties of the product. The result indicated that the flower-like product with many slender branches and hexagonal crowns at the ends were single-crystalline wurtzite structures and were preferentially oriented in the <001> direction. The photoluminescence spectrum demonstrated a strong UV emission band at about 386 nm and a green emission band at 516 nm. The field emission of the product showed a turn-on field of 3.0 V/µm at a current density of 0.1 μA/cm², while the emission current density reached about 1 mA/cm² at an applied field of 5.9 V/μm.     

Fabrication of hybrid solar cells using poly(2,5-dimethoxyaniline) hexagonal structures and zinc oxide nanorods

Flower-shaped zinc oxide (ZnO) structures have been synthesized in a microwave at 180 °C for 20 min using zinc nitrate and KOH. Detailed structural and morphology observation showed that the micron-sized ZnO nano-pencils grow out of the base of the flower-shaped ZnO structures. Photoluminescence spectrum measured at room temperature showed a sharp UV emission band around 390 nm which is attributed to the radiative annihilation of excitons. The synthesized PDMA and ZnO nanopencils are highly crystalline materials with one-dimensional morphology which improves the electron charge transport in the device. A distinctive photoluminescence quenching effect was observed indicating a photo-induced electron transfer. The solar cell devices fabricated from these materials demonstrated a short circuit current density of about 0.93 μA/cm², open-circuit voltage 0.58 V, and efficiency of 0.16 %.     

Solvothermal synthesis of hexagonal ZnO nanorods and their photoluminescence properties

Pure hexagonal ZnO nanorods were synthesized by low-temperature (90 °C) solvothermal treatment of zinc acetate in 40-80 wt.% hydrazine hydrate aqueous solutions. The products were characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. They show a strong UV emission at around 380 nm upon excitation at 360 nm using a Xe lamp at room temperature. The influence on the quality of the nanorods was investigated while the content of the solvent changed. The as-synthesized ZnO nanorods are promising materials for nanoscale optoelectronic devices due to their excellent UV emission properties.     

Synthesis and photoluminescence of Eu-doped ZnO microrods prepared by hydrothermal method

Eu-doped ZnO microrods, with wurtzite structure and [0 0 0 1] growth direction have been successfully synthesized on Si (1 0 0) substrates by a simple hydrothermal method. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), lifetime decay curves, photoluminescence (PL) and photoluminescence excitation (PLE) spectra, respectively. These results indicate that Eu³⁺ ions are located in the distorted lattice sites near the surface of the ZnO microrods. Additionally, it is also suggested that the surface defects may act as a step in the process of energy transfer from ZnO to Eu³⁺ ions.     

Study of structural and optical properties of Ge doped ZnO films

The Ge doped ZnO films were deposited on quartz substrates by radio frequency magnetron sputtering. The effects of doping and substrate temperature on the structural and optical properties of the Ge doped ZnO films were investigated by means of X-ray diffraction (XRD), UV-visible transmission spectra, X-ray photoelectron spectroscopy and photoluminescence (PL) spectra. The XRD patterns showed that Zn₂GeO₄ phases were formed in the films. With the increase of substrate temperature the crystallization of Zn₂GeO₄ was improved, and that of ZnO phases turned worse, and no diffraction peak of ZnO was observed when the substrate temperature was 700 °C. Obvious ultraviolet (UV) light emission was found due to ZnO grains, and it was much stronger than that of un-doped ZnO films. The enhancement of UV light emission at about 380 nm may be caused by excitons which were formed at the interface between Zn₂GeO₄ and ZnO grains. In the visible region of the PL spectra, the green light emission peak of samples at about 512 nm was associated with defects in ZnO. A red shift of the green light emission peak was observed which can be explained by the fact that there is a luminescence center at about 548 nm taking the place of the defect emission of ZnO with the increase of substrate temperature. The red shift of the green light emission peak and the 548 nm green light emission peaks of the PL spectrum show that some Ge²⁺ should replace the Zn²⁺ positions during the Zn₂GeO₄ grains growth and form the Ge²⁺ luminescence centers in Zn₂GeO₄ grains.     

Comparison of structural and photoluminescence properties of ZnO thin films grown by pulsed laser deposition and ultrasonic spray pyrolysis

ZnO thin films have been deposited by pulsed laser deposition (PLD) and ultrasonic spray pyrolysis (USP) method, respectively. X-ray diffraction and transmission electron microscopy characterizations indicate that ZnO film grown by PLD exhibits better crystallinity than that grown by USP. Photoluminescence spectra show that the near-band edge ultraviolet emission of film grown by PLD is narrower and shifts to higher energy, compared with that of film grown by USP. In the visible range, ZnO film grown by PLD exhibits four local level emission centered at 470 nm, 486 nm, 544 nm, and 613 nm, respectively, while the film grown by USP only presents a weak broad band emission centered at 502 nm. Hall measurement shows higher carrier density and lower hall mobility in ZnO film grown by PLD than that in film grown by USP. The higher density of intrinsic defects as well as higher crystallintiy is considered to account for the difference of photoluminescence in ZnO film grown by PLD with that in film grown by USP.