Hexagonal Microprisms Research Articles

Crystalline architectures of C84 with tunable morphology and linearly polarized red emission.

Fullerene-based micro/nano-architectures (FMNAs) with remarkable photoluminescence (PL) emissions have attracted considerable interest as potential building blocks for optical and biolabeling applications, by virtue of their low toxicity and environmentally friendly nature. Nevertheless, the PL polarization properties of FMNAs have rarely been explored. Herein, we demonstrate the preparation of highly crystalline architectures of C84, which exhibit polymorphism depending on the preparation conditions but possess similar hexagonal close-packed (hcp) structures. The PL data demonstrate that the as-prepared carambola-like hexagonal microprisms (c-HPs) show enhanced red emission compared to regular hexagonal microprisms (r-HPs). More importantly, the linear polarization of the PL emission is verified and estimated through single-prism spectroscopy, which changes from 0.42 (r-HP) to 0.58 (c-HP), comparable to those of traditional rod-like semiconductors. Thus, we demonstrate a significant correlation between the morphology and emission characteristics of C84-based microprisms, highlighting the possibility of controlling the photophysical properties of FMNAs by finely tailoring their external morphologies. This study expands the range of carbon materials with linearly polarized emissions and offers potential for use in polarization-based micro-scale sensors or detectors.

Facile Synthesis of Nb-Doped CoTiO3 Hexagonal Microprisms as Promising Anode Materials for Lithium-Ion Batteries

Bimetallic oxides are demonstrated to show better electrochemical performance than single transition metal oxides. Recently, ilmenite-type transition metal titanate (MTiO3, M = Fe, Co, Ni, etc.) is emerging as a promising anode for lithium-ion batteries (LIBs) due to its comparable theoretical capacity and small volumetric change during cycling. However, the practical electrochemical performance is still harmed by its poor electronic conductivity. Herein, for the first time, a Nb-doping strategy is adopted to modify CoTiO3 hexagonal microprisms by a facile solvothermal method combined with an annealing treatment. Benefiting from the unique 1D morphology and the ameliorated conductivities induced by Nb-doping, the optimized Nb-doped CoTiO3 anode exhibits an improved lithium-storage capacity of 233 mA h g−1 at 100 mA g−1 after 100 cycles and excellent rate capability, which are superior to that of pure CoTiO3. This work sheds light on the potential application of titanium containing bimetallic oxide in the next-generation advanced rechargeable LIBs.

Microwave-assisted controllable synthesis of 2D and 1D Eu3+-Y2O3 micro/nanoparticles and their photoluminescence properties

Rare earth elements doped yttria is a group of important functional materials used in various applications. In this work, Eu3+-Y2O3 particles with different morphology including nanoplates, porous nanoplates, quasi-triangular microprisms, hexagonal microprisms, microcylinders and nanorods have been synthesized by a facile two-step method without using any template or surfactant. The mixture of Eu(NO3)3, Y(NO3)3 and NaOH solution were irritated by microwave for 10 ​min to form the intermediate hybrid precursors, and the final Eu3+-Y2O3 were obtained by calcining the intermediate powder at 600 ​°C for 3 ​h. The morphologies, microstructure, crystal phase and composition of the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermal analysis (TG–DSC) in detail. The results show that the shapes can be controlled effectively from two dimension (2D) to one dimension (1D), and the size can be adjusted from microscale to nanoscale by changing the ratio of OH−/Re3+ only. The photoluminescence (PL) intensity and decay time of the particles vary significantly with the morphologies.

Bimetal–organic-framework derived CoTiO3/C hexagonal micro-prisms as high-performance anode materials for metal ion batteries

The CoTiO3/C synthesized by a simple morphology-controlled strategy, inhibiting structural collapse, alleviating volume expansion and facilitating the cyclic stability, exhibits a high cycle stability and high-capacity retention.

Comparative Study on Supercapacitive Performances of Hierarchically Nanoporous Carbon Materials With Morphologies From Submicrosphere to Hexagonal Microprism.

Hierarchically nanoporous carbon materials (HNCMs) with well-defined morphology and excellent electrochemical properties are promising in fabrication of energy storage devices. In this work, we made a comparative study on the supercapacitive performances of HNCMs with different morphologies. To this end, four types of HNCMs with well-defined morphologies including submicrospheres (HNCMs-S), hexagonal nanoplates (HNCMs-N), dumbbell-like particles (HNCMs-D), and hexagonal microprisms (HNCMs-P) were successfully synthesized by dual-template strategy. The relationship of structural–electrochemical property was revealed by comparing the electrochemical performances of these HNCMs-based electrodes using a three-electrode system. The results demonstrated that the HNCMs-S–based electrode exhibited the highest specific capacitance of 233.8 F g−1 at the current density of 1 A g−1 due to the large surface area and well-defined hierarchically nanoporous structure. Moreover, the as-prepared HNCMs were further fabricated into symmetrical supercapacitor devices (HNCMs-X//HNCMs-X) using KOH as the electrolyte and their supercapacitive performances were checked. Notably, the assembled HNCMs-S//HNCMs-S symmetric supercapacitors displayed superior supercapacitive performances including high specific capacitance of 55.5 F g−1 at 0.5 A g−1, good rate capability (retained 71.9% even at 20 A g−1), high energy density of 7.7 Wh kg−1 at a power density of 250 W kg−1, and excellent cycle stability after 10,000 cycles at 1 A g−1. These results further revealed the promising prospects of the prepared HNCMs-S for high-performance energy storage devices.

Selective growth and upconversion photoluminescence of Y-based fluorides: from NaYF4: Yb/Er to YF3: Yb/Er crystals

Y-based fluorides have been recognized as most efficient host materials for upconversion photoluminescence (UC-PL). Herein, we have produced a series of Yb/Er doped Y-based fluorides with specific crystal structures, shapes and sizes. The selective growth process is governed by our pre-designed surfactant 4, 4′-((2,5-bi’s (2-(diethylamino) ethoxy) −1,4-phenylene) bis (ethyne-2,1-diyl)) dibenzoic acid (DBA) and selective solvents. It is shown that highly pure hexagonal microprisms and cubic microspheres of NaYF4: Yb/Er could be selectively grown in water at low and high content of DBA, respectively, while only orthorhombic nanowires and microflowers of YF3: Yb/Er could be obtained in ethanol. Finally, all these materials obtained exhibit strong UC-PL signal while the UC emission intensity of the NaYF4: Yb/Er hexagonal microprisms is much higher than those of the cubic microspheres and orthorhombic YF3 nanowires and microflowers. This work provides a novel method for selective crystal growth of Y-based fluorides with specific shape, size, crystal phase and highly UC-PL efficiency by breaking the intrinsic limitation of crystal growth habit, which could be possibly extended to the controlled synthesis of other related materials.

Morphology Manipulation and Upconversion Luminescence Enhancement of β-NaLuF4: Er3+ Hexagonal Microtubes via Sr2+ Doping

A new and facile strategy to enhance the upconversion luminescence (UCL) emission of NaLuF4: Er3+ microcrystals (MCs) using strontium (Sr) as a dopant has been reported. With the introduction of Sr2+, the products change from long NaLuF4: Er3+ hexagonal microtubes to short hexagonal microtubes and finally to hexagonal microprisms. The growth mechanism is profoundly discussed according to the different reaction time-dependent morphologies. More importantly, the total fluorescence intensity is significantly reinforced by doping Sr2+ ions. When 18% Sr2+ is doped into NaLuF4: Er3+ hexagonal microtubes, the maximum green and red luminescence intensities are about 5.8 and 4.4 times higher than those of Sr2+-free samples, respectively. The influences of Sr2+ ion doping content on the phase, the morphology, and the local crystal field symmetry of the as-synthesized NaLuF4 crystals are investigated.

Dislocation-Free and Atomically Flat GaN Hexagonal Microprisms for Device Applications.

III-nitrides are considered the material of choice for light-emitting diodes (LEDs) and lasers in the visible to ultraviolet spectral range. The development is hampered by lattice and thermal mismatch between the nitride layers and the growth substrate leading to high dislocation densities. In order to overcome the issue, efforts have gone into selected area growth of nanowires (NWs), using their small footprint in the substrate to grow virtually dislocation-free material. Their geometry is defined by six tall side-facets and a pointed tip which limits the design of optoelectronic devices. Growth of dislocation-free and atomically smooth 3D hexagonal GaN micro-prisms with a flat, micrometer-sized top-surface is presented. These self-forming structures are suitable for optical devices such as low-loss optical cavities for high-efficiency LEDs. The structures are made by annealing GaN NWs with a thick radial shell, reforming them into hexagonal flat-top prisms with six equivalents either m- or s-facets depending on the initial heights of the top pyramid and m-facets of the NWs. This shape is kinetically controlled and the reformation can be explained with a phenomenological model based on Wulff construction that have been developed. It is expected that the results will inspire further research into micron-sized III-nitride-based devices.

P2-type Na2/3Mn1/2Co1/3Cu1/6O2 as advanced cathode material for sodium-ion batteries: Electrochemical properties and electrode kinetics

Sodium-ion batteries (SIBs) have been considered as one of foremost promising alternatives for the widely used lithium-ion batteries. In order to assemble high-performance SIBs, cathode materials with stable structure and superior electrochemical properties are needed emphatically. In this work, we prepare a new layered oxide material, P2-type Na2/3Mn1/2Co1/3Cu1/6O2 (P2-MCC) with the morphology of hexagonal micro-prisms, by a sol-gel method. When used as cathode material for SIBs, the P2-MCC exhibits good cycling stability (e.g., >83.5% capacity retention after 100 cycles at 100 mA g−1) and superior high-rate performance. Moreover, it also owns an attractive ability of fast-charging, e.g., a high capacity retention of ∼66% after 100 cycles as charging at a high current density of 200 mA g−1 and discharging at a low current density of 10 mA g−1. Such good electrochemical properties can be originated from the synergetic improvement of selected multi-metallic ions and enhanced electrode kinetics (high apparent Na-diffusion kinetics) which is demonstrated by the galvanostatic intermittent titration technique, electrochemical impedance spectroscopy and cyclic voltammetry at various scan rates.

Enhanced photon harvesting in dye-sensitized solar cells by doping TiO2 photoanode with NaYF4:Yb3+,Tm3+ microrods

An effective strategy to improve the efficiency of dye-sensitized solar cells (DSSCs) by infrared radiations (IR) and near infrared radiations (NIR) harvesting, using upconversion crystalline microrods NaYF4:Yb3+,Tm3+ is put forward. NaYF4:Yb3+,Tm3+ crystals were prepared with varying compositions of NaYF4, Yb3+ and Tm3+, and then in three different morphologies including small hexagonal microprisms, big hexagonal microprisms and hexagonal microrods for the investigation of the role of composition and morphology on upconversion efficiency. Thus, the crystals with efficient upconversion can be to screened out for doping with TiO2 photoanode of solar cells. Crystalline microrods, synthesized by hydrothermal method, show better upconversion as compared to microprisms prepared in two different sizes. On the other hand, these crystals also show downconversion. Addition of small amount of these microrods in TiO2 electrode of DSSCs increases light harvesting ability of photoanode TiO2 and consequently, photocurrent conversion efficiency is enhanced. Moreover these rare earth ions, being p-type dopant, raise the energy level of the TiO2 film and resultantly increase the photovoltage. Maximum power conversion efficiency 7.03% was achieved at an optimized proportion of NaYF4:Yb3+,Tm3+ in TiO2 (by weight). This 7.03% efficiency is 14.7% higher than the efficiency of pure TiO2 photoanode (6.13%). This improvement in efficiency can be credited to upconversion characteristics of doping material.

Monodisperse Na0.39Y0.61F2.35:Ln3+ (Ln=Dy, Tb, Eu) and NaYF4 nano-/micromaterials: Controllable morphology, porous structure, tunable multicolor and energy transfer

In this paper, monodisperse and uniform Na0.39Y0.61F2.35 (denoted as NYF hereafter) and NaYF4 nano-/micromaterials were synthesized by trisodium citrate (labeled as Cit3-) assisted one-step hydrothermal method. Various morphologies and sizes could be easily modulated by changing the ratio of reactants under the alkaline conditions, including porous nanoparticles, microrods stacked by nanospheres, turtle shell-like and hexagonal microprisms. XRD, SEM, photoluminescence (PL) and nitrogen adsorption desorption were used to characterize the prepared samples. Additionally, by co-doping the Tb3+, Eu3+ and tri-doping Dy3+, Tb3+, Eu3+ ions into the NYF host and tuning their relative concentration ratio, multicolor tunable emissions were obtained. The energy transfer process from Tb3+ to Eu3+ was studied in co-doped and tri-doped systems and demonstrated to be an exchange interaction mechanism. These results show that the NYF porous nanomaterials may have potential applications in the field of luminescence.

Facile synthesis and emission enhancement in NaLuF4 upconversion nano/micro-crystals via Y3+ doping

A series of Y3+-absent/doped NaLuF4:Yb3+, Tm3+ nano/micro-crystals were prepared via a hydrothermal process with the assistance of citric acid. Cubic nanospheres, hexagonal microdisks, and hexagonal microprisms can be achieved by simply adjusting the reaction temperature. The effect of Y3+ doping on the morphology and upconversion (UC) emission of the as-prepared samples were systematically investigated. Compared to their Y3+-free counterpart, the integrated spectral intensities in the range of 445–495 nm from α-, β-, and α/β-mixed NaLuF4:Yb3+, Tm3+ crystals with 40 mol% Y3+ doping are increased by 9.7, 4.4, and 24.3 times, respectively; red UC luminescence intensities in the range of 630–725 nm are enhanced by 4.6, 2.4, and 24.9 times, respectively. It is proposed that the increased UC emission intensity is mainly ascribed to the deformation of crystal lattice, due to the electron cloud distortion in host lattice after Y3+ doping. This paper provides a facile route to achieve nano/micro-structures with intense UC luminescence, which may have potential applications in optoelectronic devices.

Template-free synthesis of g-C3N4 microprisms for significant enhancement of photocatalytic H2 evolution under visible light

Graphitic carbon nitride (C3N4) hexagonal microprisms were synthesized via a self-assembly route using (NH4)2CO3 as a structure-directing reagent. It shows that the extraordinary hierarchical structure is favorable to improving the photocatalytic activity of C3N4 toward water splitting under visible light irradiation (λ>420nm). The photocatalytic H2-evolution rate on the microprisms is 185 µmol/h, 16.8 times higher than that over bulk C3N4. The enhanced photocatalytic performance of the as-prepared microprisms mainly originates from the characteristic micro-nanostructure, possessing enlarged surface area for efficient charge separation.

Enhanced upconversion of NaYF_4:Er^3+/Yb^3+ phosphors prepared via the rapid microwave-assisted hydrothermal route at low temperature: phase and morphology control

Monophasic NaYF4:Er(3+)/Yb(3+) crystals were synthesized via the microwave-assisted hydrothermal route at 180°C. Microwave heating during the hydrothermal process substantially reduces the duration of reaction for the formation of cubic-NaYF4:Er(3+)/Yb(3+) nanocrystals from 6 h to 30 min. As the duration of the reaction increases, cubic-NaYF4:Er(3+)/Yb(3+) nanocrystals are transformed to uniform hexagonal-NaYF4:Er(3+)/Yb(3+) microprisms because of the enhanced reaction kinetics. Bright upconverted emission from the NaYF4:Er(3+)/Yb(3+) crystal, obtained by the efficient two-photon excitation, is related to crystal structure and morphology. The hexagonal microprisms exhibit better upconversion and are employed in security applications.

Comparative SAXS, DSC and FT-IR Spectra of Polyurethane Coatings Filled with Hexagonal and Sword-like Zinc Oxide

The loading and morphology of zinc oxide (ZnO) affect the bonding and segmentation in commercial polyurethane (PU) coatings. By virtue of surface modification, hexagonal ZnO microprisms can be uniformly dispersed in PU matrix even at a loading as high as 25 wt%. However, the disruption of ZnO fillers can be observed with the suppression of characteristic PU absorption bands in Fourier transform infrared (FT-IR) spectra and the enthalpy reduction in differential scanning calorimetry (DSC) thermograms. The morphological effect is highlighted by the significant changes in DSC and FT-IR spectra when hexagonal ZnO is substituted with the sword-like counterpart. The results suggest that more sword-like ZnO can be loaded in PU coatings with a less disruption in bonding and segmentation.

Self-assembled organic hexagonal micro-prisms with high second harmonic generation efficiency for photonic devices.

Multiwavelength coherent light sources are key components for circuit integration of nanophotonics. Here, we demonstrated highly efficient second harmonic generation (SHG) in single-crystalline hexagonal micro-prisms (HMPs) of 3-methyl-4-methoxy-4'-nitrostilbene (MMONS) prepared via a facile self-assembled method. We found that the SHG conversion efficiency (ηSHG) of MMONS HMPs increases with increasing the prism side length (d). Local electric field |E|(2) calculations suggest that the symmetrical hexagonal prism shape of HMPs supports helically propagating modes. The SHG light produced at one end of HMP can be coupled into whispering-gallery (WG) like optical modes with a coupling efficiency of 50-80% and helically propagates along the length of HMPs toward another end. Based on this unique helical propagation of SHG light, we construct an optical interconnector by placing a single MMONS HMP on the top of a single micro-ribbon of 1,2-diphenyl-2-pyrazoline (DP). These easily fabricated MMONS HMPs can act as a coherent source, which adds a key component to the tool box of organic nano- and micro-structure optoelectronics.

Tunable multicolor and white-light upconversion luminescence in Yb3+/Tm3+/Ho3+ tri-doped NaYF4 micro-crystals.

NaYF4 micro-crystals with various concentrations of Yb(3+) /Tm(3+) /Ho(3+) were prepared successfully via a simple and reproducible hydrothermal route using EDTA as the chelating agent. Their phase structure and surface morphology were studied using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns revealed that all the samples were pure hexagonal phase NaYF4. SEM images showed that Yb(3+)/Tm(3+)/Ho(3+) tri-doped NaYF4 were hexagonal micro-prisms. Upconversion photoluminescence spectra of Yb(3+)/Tm(3+)/Ho(3+) tri-doped NaYF4 micro-crystals with various dopant concentrations under 980 nm excitation with a 665 mW pump power were studied. Tunable multicolor (purple, purplish blue, yellowish green, green) and white light were achieved by simply adjusting the Ho(3+) concentration in 20%Yb(3+)/1%Tm(3+)/xHo(3+) tri-doped NaYF4 micro-crystals. Furthermore, white-light emissions could be obtained using different pump powers in 20%Yb(3+)/1%Tm(3+)/1%Ho(3+) tri-doped NaYF4 micro-crystals at 980 nm excitation. The pump power-dependent intensity relationship was studied and relevant energy transfer processes were discussed in detail. The results suggest that Yb(3+)/Tm(3+) Ho(3+) tri-doped NaYF4 micro-crystals have potential applications in optoelectronic devices such as photovoltaic, plasma display panel and white-light-emitting diodes.

The Effect of Reaction Parameters on the Structural NaYF<sub>4</sub> Microcrystals

NaYF4 microcrystals were synthesized using a hydrothermal method, and the effects of the EDTA and NaF addition amount on the crystal structure, morphology and size were systematically studied. When the NaF addition amount increase, the size of the NaYF4 microcrystal increase, the excess F- ions promote the formation of β-phase of NaYF4. EDTA significantly modifies the morphology of the crystals. When addition the EDTA the crystals transition from irregular silkworm-like microcrystal to hexagonal microprisms. And the EDTA also promote the hexagonal phase formation.

One-pot Reaction To Synthesis And Characterization Of Two-stage Zinc Oxide Hexagonal Microprism On Nickel Thin Films

A novel two-stage zinc oxide (ZnO) hexagonal microprisms was successfully synthesis via a hydrothermal route on a nickel (Ni) thin films. The Ni thin films are deposited by using magnetron sputtering onto Si (100) substrate. The formation of the secondary structure and optical properties of ZnO microprism have been investigated and the formation mechanism has been discussed. The results illustrate the Ni substrate is a key factor to grow the two-stage ZnO, and the photoluminescence (PL) emission peak at 389 nm reveals that the high crystal quality of these nanorods. ZnO with its excellent luminescent properties and the controllable nanostructures will hold promise for the development of photonic devices.

Controlled growth along circumferential edge and upconverting luminescence of β-NaYF4: 20%Yb3+, 1%Er3+ microcrystals

Rational control over the uniform morphology and size of hexagonal NaYF4 has been achieved via a facile hydrothermal route. The evolution of particle morphology from peg-top-like to hexagonal microprisms with protruding centers and the long tubelike morphology with concave wedge and finally to solely microrods been demonstrated by increasing the F−/Ln3+ molar ratio, all other parameters being equal. Rationally controlling the shape of hexagonal NaYF4 is of great importance due to their strongly shape-dependent optical properties. Moreover, the systematic study on the photoluminescence of 20%Yb3+, 1%Er3+-doped β-NaYF4 with different shapes shows that the upconversion (UC) properties of these products are strongly dependent on the combined roles of morphologies, crystallinity, and particle sizes. In particular, the microrods evince a better PL signal as compared with others.