Fabrication and photoluminescent properties of heteroepitaxial ZnO/Zn0.8Mg0.2O coaxial nanorod heterostructures

ZnO/Zn0.8Mg0.2O coaxial nanorod heterostructures were prepared by employing catalyst-free metal-organic vapor-phase epitaxy, and their structural and photoluminescent (PL) properties were investigated using transmission electron microscopy (TEM) and temperature-dependent PL spectroscopy. TEM images show that ZnO/Zn0.8Mg0.2O layers were epitaxially grown on the entire surfaces of the ZnO nanorods and the ZnO nanorod diameters as a core material were as small as 9 +/- 2 nm. A dominant PL peak was observed at 3.316 eV, from room-temperature PL spectra of ZnO/Zn0.8Mg0.2O coaxial nanorod heterostructures with ZnO core diameters of 9 nm, indicating a PL blue shift of 30 meV, which resulted from a quantum confinement effect along the radial direction in ZnO nanorods. Furthermore, temperature-dependent PL properties of the coaxial nanorod heterostructures were investigated, showing much higher PL intensity for the coaxial nanorod heterostructures than that of bare ZnO nanorods at room temperature. The origin of the enhanced PL intensity and reduced thermal quenching for the coaxial nanorod heterostructures is also discussed.     

Fabrication of ZnO nanorods in ionic liquids and their photoluminescent properties

A novel and simple approach is reported to fabricate uniform single-crystal ZnO nanorods in ionic liq-uids. The as-obtained ZnO nanorods have been characterized by XRD,TEM,HRTEM,SAED,XPS,EDXA,PL and UV-vis absorption spectra. The rod diameters of the nanostructures can be controlled by tuning the amount of sodium hydroxide in the synthesis. Photoluminescence results show that the nanos-tructural ZnO exhibits better optical properties than bulk ZnO does and interestingly,the smaller the rod diameters are,the better optical property 1D nanostructural ZnO exhibits. The possible growth mechanism of ZnO nanorods is also investigated.     

Electrical transport properties of Zn doped ZnO

Electrical resistivity and Hall effect measurements at 77–373°K are presented for Zn doped ZnO crystals. The crystals have been doped systematically at 600–1100°C in controlled pressures of Zn. The concentration of electrons at room temperature is in the range n_RT = 2.5 × 10¹⁶, to 3.6 × 10¹⁸, cm^?3. The donor level E_D and the concentrations of donors N^D and acceptors N_A have been calculated from a best fit to the experimental relationships log n versus $\text{1}\text{T}$ and log μ_H versus log T. At dilute concentrations of donors, two donor levels have been observed, E_D^I = 0.043–0.045 eV and a deeper level E^II_D greater than 0.165 eV. The ZnO was found to behave as a metal at N_D ～ 6 × 10¹⁸, cm^?3.At least two different donors have to be assumed in order to explain the experimental results. It is suggested that interstitial Zn is the electrical active donor at higher doping levels. The nature of the other donor is not clear. Neither 1s¹ H-type nor 1s² He-type donors seem to explain all the observations consistently.     

MgAl2O4:Eu3+ nanoplates and nanoparticles as red-emitting phosphors: Shape-controlled synthesis and photoluminescent properties

We demonstrate herein a facile hydrothermal synthesis followed by post-annealing approach to selectively prepare MgAl₂O₄:Eu³⁺ nanoplates and nanoparticles. Series of scientific techniques such as XRPD, FESEM, TEM, HRTEM, and PL were adopted to characterize the as-prepared MgAl₂O₄:Eu³⁺ phosphors. First, by altering the amount of hexamethylenetetramine (abbr. HMTA) in solution, MgAl₂O₄:Eu³⁺ nanoplates occurred. Next, MgAl₂O₄:Eu³⁺ nanoparticles were prepared by adding certain amounts of sodium citrate and sodium dodecylbenzenesulfonate (abbr. SDBS). In particular, the MgAl₂O₄:Eu³⁺ nanoplates have novel porous structures. Besides, the MgAl₂O₄:Eu³⁺ phosphors exhibit excellent red-emitting properties based upon the characteristic transitions of Eu³⁺ from ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, and 4).     

Fabrication and photoluminescent properties of ZnO/mesoporous silica composites templated by a chelating surfactant

A novel anionic surfactant-templated synthesis of ZnO/mesoporous silica nanocomposites has been carried out by using N-hexadecylethylenediamine triacetate (HED3A), a triprotic surfactant, as the structure-directing agent. The chelating template can capture zinc ions in solution and then direct the mesophase formation, enabling an amount of zinc oxide to be embedded in the porous silica matrix during calcination. With variation of the molar ratio of Zn(2+) to HED3A in the template, a series of composites with different doping amounts were obtained after the removal of organic components. The variation of the zinc ion concentration in the initial template solution induces an evolution of the silica mesophase, presumably due to the change in electronegativity of the HED3A headgroup caused by the chelating effect. Spectroscopic studies show a strong host-guest interaction between the silica pore walls and ultrafine ZnO nanoparticles. The photoluminescence properties of the resulting composites exhibit a size-dependent light emission and quantum-confinement effect of ZnO, accompanied by an infrequent violet emission originating from the ZnO-SiO(2) interface.     

Facile synthesis of novel photoluminescent ZnO micro- and nanopencils

A single-step solvent-, catalyst-, and template-free synthesis process to prepare photoluminescent pencils of ZnO either in micro- or in nanosize diameters from a single precursor is demonstrated. The thermolysis of Zn's acetate dihydrate (ZAD) precursor in a closed stainless steel reactor at 700 degrees C under autogenic pressure (6.5 MPa), yielded carbon sphere-decorated ZnO micropencils (ZnO-M's). The ZnO-M's have novel room-temperature photoluminescence (PL) with well-defined emission peaks at the green, yellow, orange, and red regions of the visible spectra while suppressing the blue region. On the contrary, the thermolysis of ZAD in a closed stainless steel reactor at 700 degrees C with released pressure yielded uniformly carbon-coated ZnO nanopencils (ZN's). The coated carbon in ZN's quenches the complete UV-vis PL; however, after annealing ZN's at 600 degrees C/2 h in air, the UV PL is dominant, and the visible PL is suppressed. The carbon coating (partly or completely) on the one-dimensional (1D) ZnO surfaces plays an important role to modify PL properties. The insight into the reaction mechanism was gained through in situ mass spectrometry measurements. The as-prepared ZnO-M's and ZN's have been systematically characterized to determine their morphology, structure, and composition.     

Enhancement of electrochemical and photoelectrochemical properties of fibrous Zn and ZnO electrodes

Zinc and zinc oxide electrodes with fibrous morphologies were prepared to exploit their high interfacial areas and superior electrical conductivity for the enhancement of electrochemical and photoelectrochemical properties.     

Microwave plasma growth and high spatial resolution cathodoluminescent spectrum of tetrapod ZnO nanostructures

A novel microwave plasma assisted by tube furnace heating system is designed to grow tetrapod ZnO nanostructures. Under optimal reaction conditions, Zn powder is oxidated to form the tetrapod ZnO with straight and uniform four legs (nanorods), bearing diameters ranging from 10 to 25 nm and lengths up to 160 nm. High-resolution transmission electron microscopy analyses reveals that the tetrapod ZnO nanostructures are perfect crystalloid. High spatial resolution cathodoluminescent spectrum for individual tetrapod ZnO nanostructure shows only a strong ultraviolet emission at 385 nm.     

Europium-doped calcium pyrophosphates: Allotropic forms and photoluminescent properties

In a search for new luminescent biological probes, we synthesized calcium pyrophosphates doped with europium up to an atomic Eu/(Eu+Ca) ratio of 2%. They were prepared by coprecipitating a mixture of calcium and europium salts with phosphate. After heating at 900 °C in air, two phases coexisted, identified as the β calcium pyrophosphate form and EuPO₄. Heating near 1250 °C in air, during the β→α transformation, europium ions substitute for calcium ions in the α calcium pyrophosphate structure as demonstrated by the spectroscopic study. Europium ions with both valence states (divalent and trivalent) were observed in the samples. Following the synthesis procedure, partial reduction of Eu³⁺ took place even in an oxidizing atmosphere. The 0.5%-doped compound could serve as a sensitive probe in biological applications. Depending on the excitation wavelength, the luminescence occurs either in the red or in the blue regions, which discriminates it from parasitic signals arising from other dyes or organelles in live cells.     

Systematic investigation on morphologies, forming mechanism, photocatalytic and photoluminescent properties of ZnO nanostructures constructed in ionic liquids

In this contribution, a series of shape-controllable ZnO nanostructures were synthesized in ionic liquids by a simpler, only one-step, low-temperature route, and characterized by XRD, XPS, TEM, HRTEM, SAED, EDXA, SEM, FTIR, surface area measurement and photoluminescence. We mainly investigate the effect of cations of ionic liquids on the shape of ZnO nanostructures and the forming mechanism of ZnO nanostructures in ionic liquids, as well as the luminescent property and photocatalytic activity for the degradation of Rhodamine B. The results show that the longer alkyl chain at position-1 of the imidazole ring of the ionic liquid will hinder the ZnO nanostructures from growing longer, and the hydrogen bonds may play a crucial role for the directional growth of the 1D nanocrystals. The photoluminescent study shows that the as-obtained ZnO nanostructures exhibit a unique green emission, indicating the existence of oxygen vacancies in the ZnO nanostructures. Importantly, the as-obtained ZnO nanostructures prepared in different ionic liquids show strong size/shape-dependent photocatalysis activity for degradation of Rhodamine B, and the well-dispersed homogeneous ZnO nanoparticles and nanowires display high photocatalytic activity. The investigation of photodegradation kinetics of Rhodamine B indicates that the photodegradation process obeys the rule of a first-order kinetic equation ln( C(0)/ C) = kt. This is the first systematic investigation on the relationship between the structure of ionic liquids and the morphology of ZnO nanostructures.     

Synthesis and photoluminescent properties of new ceramidine derivatives

A series of new ceramidine derivatives 8a–f has been synthesized in 4–5 steps involving a Wittig reaction of ceramidonine with various triphenylphosphonium bromides. Their UV and photoluminescence (PL) properties are reported. The compounds showed medium to strong PL between 502 and 522 nm at a concentration of 1 × 10⁻⁵ M CH₂Cl₂. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:66–73, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20753     

Phase behavior and anisotropic optical properties of photoluminescent polarizers

The phase behavior and anisotropic optical properties of tensile deformed blends of a photoluminescent polymer guest in an ultra‐high molecular weight polyethylene matrix were studied on the level of single molecules by means of scanning confocal optical microscopy. It is shown that upon tensile deformation of the blends, the system transforms from a phase‐separated system into a quasi‐molecular solid solution. The influence of this phase transition on the anisotropic optical properties of oriented blend films was also investigated with polarized steady‐state photoluminescence spectroscopy. We show that well‐dissolved guest molecules tend to reach higher degrees of orientation at lower draw ratios of the blend films compared to guests that phase‐separate from the matrix polymer. Dichroic ratios in emission in the range of 50 were observed in optimized blend films based on photoluminescent oligomers and linear low density polyethylene.     

Synthesis and photoluminescent properties of new cationic carbazole-containing luminophores

The synthesis of a series of new π-conjugated amphiphilic derivatives of carbazole of the "stilbene" type, substituted with N-alkylpyridinium groups at positions 2 and 7, is described. Due to the presence of polar cationic groups and nonpolar alkyl substituents, the obtained compounds are potentially capable of acting as agents for the transportation of genetic material inside a cell, and the extended and effective conjugation chain leads to the appearance of intense photoluminescence both in solutions and in biological media, making it possible to use them as cell probes. The absorption maxima of the compounds are in the region of 422-450 nm, while the luminescence maxima are in the yellow-green region at 575-617 nm.     

Synthesis and photoluminescent properties of 1,1'-binaphthyl-based chiral phenylenevinylene dendrimers

New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6'-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1'-binaphthyl derivative (R)-1 and the appropriate dendrons (R)(2n)G(n)-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, the redox properties of the dendrimers were determined by cyclic voltammetry, showing the influence of the functional groups at the peripheral positions of the dendrimer on the redox behavior of these systems.     

Hydrothermal synthesis and photoluminescent properties of stacked indium sulfide superstructures

Unusual hierarchical stacked superstructures of cubic beta-In2S3 were fabricated via a facile hydrothermal process in the presence of a surfactant cetyltrimethylammonium bromide CTAB; the 3D superstructures were developed by helical propagation of surface steps from microflakes of 10-20 nm thickness.     

Facile sonochemical synthesis and photoluminescent properties of lanthanide orthophosphate nanoparticles

Uniform lanthanide orthophosphate LnPO₄ (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho) nanoparticles have been systematically synthesized via a facile, fast, efficient ultrasonic irradiation of inorganic salt aqueous solution under ambient conditions without any surfactant or template. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) spectra as well as kinetic decays were employed to characterize the samples. The SEM and the TEM images show that the hexagonal structured lanthanide orthophosphate LnPO₄ (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd) products have nanorod bundles morphology, while the tetragonal LnPO₄ (Ln=Tb, Dy, Ho) samples prepared under the same experimental conditions are composed of nanoparticles. HRTEM micrographs and SAED results prove that these nanostructures are polycrystalline in nature. The possible formation mechanism for LnPO₄ (Ln=La-Gd) nanorod bundles is proposed. Eu³⁺-doped LaPO₄ and Tb³⁺-doped CePO₄ samples were also prepared by using the same synthetic process, which exhibit an orange-red (Eu³⁺:⁵D₀-⁷F_{1, 2, 3, 4}) and green (Tb³⁺, ⁵D₄-⁷F_{3, 4, 5, 6}) emission, respectively.     

Eu3+- and Ho3+-doped Ba3Al2O6- and MgAl2O4-type phosphors and their photoluminescent properties

Journal of Thermal Analysis and Calorimetry - The aluminate hosts were basically activated with the Eu3+- and Ho3+-ions which were prepared by solid-state reaction in this study. The DTA/TG results...     

Four Co(II)/Zn(II) coordination polymers with a multidentate ligand: syntheses,structures, thermal,and photoluminescent properties

Two pairs of isostructural transition metal coordination polymers, {[Co(L)(H₂O)]_n} (1) and {[Zn(L)(H₂O)]_n} (3), {[Co(L)(4,4′-bipy)(H₂O)]·H₂O}_n (2) and {[Zn(L)(4,4′-bipy)(H₂O)]·H₂O}_n (4) (H₂L = N-pyrazinesulfonyl-glycine acid and 4,4′-bipy = 4,4′-bipyridine), have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental and thermogravimetric analyses. The structures show that 1 and 3 display 2-D polymeric grid frameworks with a 3-connected (4, 8²) topology. 2 and 4 also exhibit a 2-D polymeric grid structure, but are constructed by a 4-connected (4, 4) topology. The adjacent 2-D polymeric grid frameworks for 1–4 are further linked by hydrogen bonding O–H?O interactions to form 3-D supramolecular interweaved orderly networks. The fluorescent properties of 3 and 4 were investigated in the solid state.