Surface Quantum-Dimensional Photocarrier Recombination in CdTe Microcrystals

The scope of the study is the spectra of low-temperature (T = 2K) photoluminescence of a p-CdTe/n-CdS film heterostructure comprising a monolayer of CdTe microcrystals, where a single microcrystalline particle is typically one micron in size. Focus is made on the dominant band of “super-hot” emission appearing in the spectral region located in energy above the fundamental absorption edge of a CdTe bulk crystal. A theoretical model has been developed that assumes the existence of a space-charge layer inside a microcrystal, which leads to the formation of a triangular potential well for an electron near the surface. The anomalous emission band arises as a result of the optical transitions of electrons from near-surface levels of spatial quantization to valence band states.

The Early Strength of Slag Cements with Addition of Hydrate Microcrystals

The effect of hydrate microcrystals such as calcium silicate hydrates ( CSH) and ettringite on the early strength of slag cements was studied. The authors explored the possibility of improving the early strength of the slag cement by applying crystal seed technology. It is shown that slag crystal seeds make the early strength of the cement increased due to the action of hydrate crystal seeds , which speed up the hydration of clinker minerals in the nucleation of ettringite. Therefore, the early strength of the slag cement is obviously improved.

Formamidinium Lead Bromide (FAPbBr_3) Perovskite Microcrystals for Sensitive and Fast Photodetectors

Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material than conventional CH_3NH_3-PbX_3(MAPbX_3). Herein, we fabricated a FAPbBr_3 microcrystal-based photodetector that exhibited a good responsivity of 4000 A W-1 and external quantum efficiency up to 106% under one-photon excitation, corresponding to the detectivity greater than 1014 Jones. The responsivity is two orders of magnitude higher than that of previously reported formamidinium perovskite photodetectors. Furthermore, the FAPbBr_3 photodetector's responsivity to two-photon absorption with an 800-nm excitation source can reach 0.07 A W^(-1), which is four orders of magnitude higher than that of its MAPbBr_3 counterparts. The response time of this photodetector is less than 1 ms.This study provides solid evidence that FAPbBr_3 can be an excellent candidate for highly sensitive and fast photodetectors.

Synthesis and Upconversion Luminescence of LaF_3:Yb^(3+),Er^(3+)/SiO_2 Core/Shell Microcrystals

LaF3：Yb^3＋ , Er^＋ microcrystals were synthesized by a hydrothermal method, and then, the LaF3： Yb^3＋ , Er^＋ microcrystals were coated with silica. Phase identification of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 was performed via XRD. The TEM image showed that the size of LaF3： Yb^3＋ , Er^＋ was 150 nm and LaF3： Yb^3＋ , Er^＋/SiO2 presented clearly a core/shell structure with 20 nm shell thickness. The upconversion spectra of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 in solid state and in ethanol were studied with a 980 nm diode laser as the excitation source. The upconversion spectra showed that the silica shell had little effect on the properties of fluorescence of the LaF3：Yb^3＋ , Er^＋ microcrystals. At the same time, the green luminescence photo of LaF3： Yb3＋, Er3＋/SiO2 in the PBS buffer was obtained, which indicated that the LaF3： Yb^3＋ , Er^＋/SiO2 could be used in biological applications.

Intra-Articular injection of acid-sensitive stearoxyl-ketal-dexamethasone microcrystals for long-acting arthritis therapy

Despite advances in treatment of chronic arthritis,there is still a strong need for the development of long-acting formulations that can enable local and sustained drug release at the inflamed tissues.In this work,we fabricated microcrystals of an acid-sensitive stearoxyl-ketal-dexamethasone prodrug for treatment of arthritis.Microcrystals of the prodrug with two sizes were successfully engineered and showed pH-dependent hydrolysis kinetics in vitro.In a collagen-induced arthritis rat model,we evaluated the influence of particle size and injection dose on anti-inflammatory effect after intra-articular injection.Such prodrug demonstrated long-acting anti-arthritis effects with good safety.Our results indicate ketal-based prodrugs are promising for the development of long-acting injectables and may stimulate the development of new treatments for chronic diseases.

Ag3PO4 Microcrystals Synthesized by Room-Temperature Solid State Reaction:Enhanced Photocatalytic Activity and Photoelectronchemistry Performance

Ag3PO4 microcrystals with highly enhanced visible light photocatalytic activity are prepared by a facile and simple solid state reaction at room temperature. The composition, morphology and optical properties of the asprepared Ag3PO4 microcrystMs are characterized by x-ray diffraction, scanning electron microscopy and UV-vis diffuse reflectance spectra. The photocatalytie properties of Ag3PO4 are investigated by the degradation of both methylene blue and methyl orange dyes under visible light irradiation. The as-prepared Ag3PO4 microcrystals possess high photocatalytic oxygen production with the rate of 673μmolh-1g-1. Moreover, the as-prepared Ag3PO4 microcrystals show an enhanced photoelectrochemistry performance under irradiation of visible light.

Effect of annealing on structural and optical properties of lead tungstate microcrystals

Shuttle-like lead tungstate （PbWOa） microcrystals are synthesized at room temperature using the precipitation method with the cetyltrimethyl ammonium bromide. Results from both the X-ray diffraction and the scanning electron microscopy show that the lattice distortions of the PbWO4 microcrystals are reduced significantly when the annealing temperature is increased to 873 K. The result from the ultraviolet-visible diffuse reflectance spectroscopy shows that the exciton absorption appears in the sample annealed at 673 K. The self-trapped exciton luminescence due to the Jahn- Teller effect is also observed in the blue band. The interstitial oxygen ions in the WO42- groups are mainly resposible for the enhancement effect of the green luminescence of the annealed samples. The above results are supported by the spectrum analysis of the as-grown and the post-annealed samples using the X-ray photoelectron spectroscopy.

LOCALIZED CORROSION OF MICROCRYSTALS OF 1Crl8Ni9Ti STAINLESS STEEL

The resistances against localized corrosion of 1Cr18Ni9Ti microcrystals with normal grain size and bcc structure obtained hy magnetron sputtering have been compared.The two kinds of microcrystals with (110) and (211) textures respectively were obtained under different sputtering conditions.Both microcrystals were found to have better resistance against local- ized corrosion than the crystal with normal grain.The microcrystal with (110) preferred orientation has larger resistance to localized corrosion than that with (211) preferred orientation.

Facile Synthesis of 2PbCO_3·Pb(OH)_2 Microcrystals and Its Catalytic Behavior for Transesterification of Dimethyl Carbonate with Phenol

Polyhedron lead hydroxide carbonate （2PbCO3·Pb（OH）2 ） microcrystals have been prepared in solution phase via a facile method in the presence of surfactant cetyltrimethylammonium bromide （CTAB）. All the samples were characterized by powder X-ray diffraction ,pattern （XRD）, field-emission scanning electron mi- croscopy （FE-SEM）, high-resolution transmission electron microscopy （HRTEM）, and selected area electron diffraction （SAED）. The possible growth mechanism was discussed. 2PbCO3·Pb（OH）2 microcrystals were found to be a novel and efficient catalyst for the synthesis of diphenyl carbonate （DPC） by transesterification of dimethyl carbonate （DMC） with phenol. Compared with some other catalysts, such as AlCl3, ZnCl2, and Mg5（CO3）4（OH）2, 2PbCO3·Pb（OH）2 microcrystals are stable and show relatively high activity at low catalyst amount. When the reaction was carried out at 180 12, with a molar ratio of phenol to DMC of 2：1, a reaction time 14 h, and a catalyst amount 0.2% （molar ratio to phenol）, the selectivity of DPC and methyl phenyl carbonate （MPC） was 14.7% and 78.8%, respectively.

One-pot synthesis of hexagonal NaLuF_(4):Yb,Er microcrystals with enhanced upconversion emission and high production yield

In this work,monodisperseβ-NaLuF_(4):Yb,Er microcrystals with intense upconversion emission were synthesized via a modified hydrothermal method.With the increase of reactant concentration,their production yield is increased obviously,and the upconversion emission intensity inβ-NaLuF_(4):Yb,Er microcrystals is also enhanced significantly.The luminescence enhancement should be attributed to minimal internal OH defects,validated by a combination of analytical X-ray diffraction(XRD),energy dispersive spectrum(EDS),and Eu^(3+)structural probe measurements.We also reveal that high Na^(+):RE~(3+)ratio in theβ-NaLuF_(4):Yb,Er microcrystals prepared under Na^(~)+-rich reaction will arouse the increased repulsive energy ofβ-NaLuF_(4)microcrystals between F^(~)-and OH^(~)-anions and then facilitate the substitution of large OH^(-)ions by small F^(~)-ions under F^(~)--rich reaction conditions.Minimal OH^(-)concentrations can limit nonradiative relaxation and promote excitation energy harvesting for high upconversion efficiency.The presented results not only offer a facile method for the simultaneous production yield and luminescence intensity increase ofβ-NaREF_(4)microcrystals,but also uncover a better insight into the upconversion emission alterations,which is favorable to broaden their practical applications.

Controlled synthesis and magnetic properties of Fe_3O_4 walnut spherical particles and octahedral microcrystals

Magnetite Fe3O4 walnut spherical particles and octahedral microcrystals were suc- cessfully synthesized from K4 [Fe (CN) 6], K3 [Fe (CN) 6] and NaOH reagents via a simple hydrothermal process. And the uniform morphology of octahedral micro- crystals was obtained in the presence of ethylene glycol. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the Fe3O4 walnut spherical particles and octahedral microcrystals were single crystals with the face-center cubic structure and with size distributions from 2.2 to 8.6 μm and 1.6 to 12.5 μm, respectively. Their magnetic properties were detected by a vibrating sample magnetometer at room temperature. The walnut spherical parti- cles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) being 150.57 Oe, 97.634 and 12.05 emu/g, respectively. For the octahedral microcrystals they were 75.28 Oe, 101.90 and 6.69 emu/g, respectively. Different sizes of walnut spherical particles were controlled synthesized through adjusting the NaOH concentration. It was found that ethylene glycol molecules have a significant effect on the formation of Fe3O4 octahedra. A possible mechanism was also proposed to account for the growth of these Fe3O4

Preparation and characterization of NaYF_4:Er^(3+),Tm^(3+)@NaYF_4:Ce^(3+),Tb^(3+) microcrystals with dual-mode emissions at the single-particle level

Under hydrothermal environment,we synthesized lanthanide ions doped sodium yttrium fluoride(NaYF4:Er,Tm@NaYF4:Ce,Tb) luminescent microcrystals via an epitaxial growth technique.The structure and morphology of these microcrystals were examined by SEM,TEM,EDS and XRD measurements.These particles show dual-mode emissions with red upconversion(UC) and green down conversion(DC) as single particles level.The mean length and diameter of these microparticles increase from 0.43 to2.26 μm and from 1.33 to 1.86 μm,respectively.Most interestingly,the photoluminescence properties of NaYF4:Er,Tm@NaYF4:Ce,Tb phosphor crystals are highly dependent on the crystallite size.The microcrystals fluoresce emit dual-mode emissions when they are solid or dispersed in solvents.Benefiting its intensive fluorescence and uniform morphology,these materials hold great potential for security and anti-counterfeiting applications.

Synthesis and characterization of branched yttrium hydroxide fluoride microcrystals with hierarchical tubular structure

Hexagonal yttrium hydroxide fluoride microcrystals were prepared by a two-step hydrothermal routte using yttrium nitrate, sodium hydroxide and sodium fluoride as raw materials to react in propanetriol solvent. The samples were characterized by powder X-ray diffraction （XRD）, energy dispersive spectrum （EDS）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, Fourier trans- form infrared spectroscopy （FT-1R）, thermogravimetre and differential-thermogravimetric analysis （TG-DTA）, which revealed that Y（OH）2.14F0.86 microerystals were multi-branched and that the branches of Y（OH）2A4F0.86 microcrystals were composed of hierarchical tubes. This novel multi-branched and intriguing hierarchical tubular structure of yttrium hydroxide fluoride maybe has a potential application in photoelectric crystals. The formation of branched Y（OH）2.14F0.86 microcrystals with hierarchical tubular structure were due to the substitution reaction and Oswald ripening.

Optical properties of nano-size ZnS semiconductor microcrystals doped with Mn^(2+) ions

In recent years, me synthesis and optical properties of nano-size semiconductor particles were studied more extensively. Semiconductor (such as ZnS, CdS and GaP) nanometer microcrystallites were prepared in polymers, organic solutions and glasses. The quantum-size effects occurred and the optical properties were changed in those materials as the microcrystal radius decreased. Most of the previous studies were devoted to understanding the intrinsic properties and the interaction with surrounding medium. Bhargava

Effect of Oxygen Admittance Temperature on the Growth of ZnO Microcrystals by Thermal Evaporation Technique

Hexagonally well-faceted microcrystals of ZnO have been grown by thermal evaporation of Zn powder in oxygen ambient at 700℃ under atmospheric pressure. It has been observed that the properties （size and quality） of ZnO microcrystals have a strong dependence on the reactor temperature at which the oxygen gas is admitted into the growth zone. The microcrystals grown with oxygen admittance at 450℃ have a length of 1 μm and a diameter of 0.75 μm while that grown with oxygen admittance at 600 ℃ have a length of 1.5-2 μm and a diameter of 1 μm. Room temperature photoluminescence spectra show a ultraviolet （UV） emission peak at 385 nm with a green band emission at around 500 nm. The UV-to-green band emission ratio for the microcrystals grown with oxygen admittance at 450℃ is observed to be 1.25 and the ratio decreases to 0.45 for the sample grown with oxygen admittance at 600℃.

CTAB Assisted Synthesis of CuS Microcrystals:Synthesis,Mechanism,and Electrical Properties

CuS microcrystals were successfully prepared through a mild solvothermal reaction in ethylene glycol （EG） with the assistance of cationic surfactant cetyltrimethylammonium bromide （CTAB）. An interesting morphology evolution from flower-like microspheres to hollow microspheres, and finally to smooth nanoflakes was observed when increasing the amount of CTAB. The products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and UV-vis spectroscopy. It was found that the amount of CTAB played an important role in determining the morphology of the CuS microcrystals. Electrical measurement reveals that the as-prepared CuS microspheres were of high conductivity, which might favor their device applications. It is expected that CuS microcrystals with controlled morphologies and structures will have important applications in solar cells. This simple but effective method could also be extended to the controlled growth of other inorganic microcrystals.

Rational self-assembly of polygonal organic microcrystals for shape-dependent multi-directional 2D optical waveguides

Micro-nano-level photonic waveguide regulation is essential for future on-chip photonic integrated systems and is still of great challenges.We report a molecular design strategy,changing the position of the methyl substituent makes the arrangement of the three isomer molecules different in their respective crystals.Based on this strategy,three sheet-like crystals with different polygonal morphologies were prepared via solution self-assembly approach.The in-depth optical measurements demonstrated that these three microsheet crystals have different 2D optical waveguide performances related to the shapes.Our work provides a feasible design strategy and material preparation method for realizing precise 2D optical waveguide modulation,which lays the foundation for complex photonic integrated systems in the future.

Tuning the face orientation of ZnO nano/microcrystals by a wet chemical method

We successfully synthesize four kinds of ZnO nano/microcrystals including dumbbell microrods, nanoflakes, nanoplates, and microrods by a simple wet chemical method. Growth duration is found to play a crucial role in the morphologies of these ZnO nano/microcrystallites. In addition, growth conditions are systematically studied as a function of precursor concentration and temperature. The structural and optical characteristics of the ZnO samples are further investigated by X-ray diffraction, scanning electron microscopy, and photoluminescence spectroscopy.

Spectra of excitons in R-phycoerythrin microcrystals

The antenna system of photosynthetic organisms serves to absorb light energy andtransfer excitation energy to the reaction centers. Energy transfer in the antenna system hasbeen found to be very efficient and rapid. The overall transfer efficiency exceeds 90％, andthe whole process of energy transfer from the phycoerythrin (PE) to the reaction center iscompleted within 50 ps in intact cells of red algae and cyanobacteria. Phycobilisome. the important photosynthetic antenna in red algae and cyanobacteria,consists of antenna polypeptide rods and core. One side of the core attaches to thethylakoid membrane and connects with the reaction center. the other side connects with

Hydrothermal Synthesis, Characterization and Photoluminescence Properties of GdOHCO3 Rhombic Microcrystals

GdOHCO3 rhombic microcrystals were synthesized by hydrothermal method with urea used as the preci- pitator. Experimental parameters, such as the molar ratio of the starting reagents, reaction temperature and reaction time were examined. The as-obtained product was characterized by powder X-ray diffraction（XRD）, field-emission scanning electron microscopy（FESEM）, X-ray photoelectron spectroscopy（XPS）, Fourier transform infrared spec- troscopy（FTIR） and spectrofluorometry. The main reactions to form GdOHCO3 were proposed. In addition, the pho- toluminescence（PL） properties of GdOHCO3 rhombic microcrystals were discussed. The broad band located between 350 nm and 600 nm in the emission spectrum can be attributed to the self-trapped exciton luminescence.