Three-Dimensional Cuprous Lead Bromide Framework with Highly Efficient and Stable Blue Photoluminescence Emission

Considering the instability and low photoluminescence quantum yield (PLQY) of blue-emitting perovskites, it is still challenging and attractive to construct single crystalline hybrid lead halides with highly stable and efficient blue light emission. Herein, by rationally introducing d¹⁰ transition metal into single lead halide as new structural building unit and optical emitting center, we prepared a bimetallic halide of [(NH₄)₂]CuPbBr₅ with new type of three-dimensional (3D) anionic framework. [(NH₄)₂]CuPbBr₅ exhibits strong band-edge blue emission (441 nm) with a high PLQY of 32 % upon excitation with UV light. Detailed photophysical studies indicate [(NH₄)₂]CuPbBr₅ also displays broadband red light emissions derived from self-trapped states. Furthermore, the 3D framework features high structural and optical stabilities at extreme environments during at least three years. To our best knowledge, this work represents the first 3D non-perovskite bimetallic halide with highly efficient and stable blue light emission.     

Selective and Tunable Near‐Infrared and Visible Light Transmittance of MoO3−x Nanocomposites with Different Crystallinity

In this Communication, we report MoO_3−x nanocomposites in which the near‐infrared and visible light transmittance can be selectively modulated through the crystallinity. The MoO_3−x nanocomposites were fabricated by a hydrothermal method, and their optical properties were characterized by UV‐Vis spectrometer. The obtained results proved the possibility to tune the nanocomposite's optical properties in the UV/Visible spectral region: crystalline MoO₃ mainly regulates the near‐infrared range (800–2600 nm), and amorphous MoO_3−x mainly changes the visible range from 350 nm to 800 nm and MoO_3−x , with semi‐crystalline structures mainly modulating around 800–1000 nm. These kinds of optical modulations could be attributed to small polar absorption, free electron absorption and plasmon absorption according to different crystallinity. Our work may create new possibilities for future applications such as photochromism, photocatalysis, and electrochromism.     

Three‐Dimensional Cuprous Lead Bromide Framework with Highly Efficient and Stable Blue Photoluminescence Emission

Considering the instability and low photoluminescence quantum yield (PLQY) of blue‐emitting perovskites, it is still challenging and attractive to construct single crystalline hybrid lead halides with highly stable and efficient blue light emission. Herein, by rationally introducing d¹⁰ transition metal into single lead halide as new structural building unit and optical emitting center, we prepared a bimetallic halide of [(NH₄)₂]CuPbBr₅ with new type of three‐dimensional (3D) anionic framework. [(NH₄)₂]CuPbBr₅ exhibits strong band‐edge blue emission (441 nm) with a high PLQY of 32 % upon excitation with UV light. Detailed photophysical studies indicate [(NH₄)₂]CuPbBr₅ also displays broadband red light emissions derived from self‐trapped states. Furthermore, the 3D framework features high structural and optical stabilities at extreme environments during at least three years. To our best knowledge, this work represents the first 3D non‐perovskite bimetallic halide with highly efficient and stable blue light emission.     

Large‐Scale Synthesis of Necklace‐Like Single‐Crystalline PbTiO3 Nanowires

Summary: We show in this communication that large‐scale necklace‐like single‐crystalline tetragonal perovskite PbTiO₃ nanowires can be obtained via a simple electrospinning method. The morphology and the crystal structure are investigated by SEM, XRD, and HRTEM. The length of the necklace‐like PbTiO₃ nanowires is from tens to several tens of micrometers, the wider the diameter of it is between 100 and 200 nm and the thinner the part is between 20 and 50 nm. The necklace‐like PbTiO₃ nanowires exhibit high surface photovoltage under the action of external electric field, which is probably applicable in displaying photoelectric devices of heterojunction structure.

SEM image of the electrospinning necklace‐like PbTiO₃ nanowires.     

Electrorheology and characterization of acrylic rubber and lead titanate composite materials

Oxide one‐pot synthesis was used to synthesize a polymer precursor to lead titanate, PbTiO₃. Perovskite lead titanate, PbTiO₃, was synthesized via the sol–gel process. The dielectric constant, electrical conductivity and loss tangent of our acrylic rubber (AR71)–lead titanate (PT) composite material (AR/PT_8) were 14.15, 2.62 × 10^?7/Ω m, and 0.093, respectively, measured at 27 °C and 1000 Hz. SEM micrographs of composites between the AR71 elastomer and PbTiO₃ showed that the particles were reinforced within the matrix. The electrorheological properties of the AR71/PT composites were investigated as functions of electric field strength from 0 to 2 kV/mm and PbTiO₃ particle volume fraction. The storage modulus increased linearly with particle volume fraction, with or without an electric field. Without an electric field, the particles merely acted as a filler to absorb or store additional stress. With the electric field on, particle‐induced dipole moments were generated, leading to interparticle interactions, and thus a substantial increase in storage modulus. With PbTiO₃ particle volume fractions as small as 10^?4 embedded in the elastomer matrix, the modulus increased by nearly a factor of 2 as the electric field strength varied from 0 to 2 kV/mm. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and spectroscopic characterization of Mn(II) doped organic amine templated chlorocadmiumphosphate CdHPO4Cl · [H3N(CH2)6NH3]0.5 crystals

Chlorocadmiumphosphate CdHPO₄Cl?·?[H₃N(CH₂)₆NH₃]_0.5 crystals doped with Mn(II) are grown at room temperature via organic amine template method and characterized by spectroscopic techniques to obtain information on the nature of the incorporated Mn(II). Powder X-ray diffraction patterns of the sample are indexed to monoclinic cell and average crystalline size is found to be around 55?nm. The optical absorption spectrum exhibits various bands which are characteristic of Mn(II) in distorted octahedral site symmetry, confirmed by characteristic resonance signal at g?=?2.018 observed in the EPR spectrum. Fourier transform infrared spectrum shows the specific vibrations of phosphate and organic molecules. Thermal curves indicate that the crystal is stable at 307°C; above this temperature crystal structure disintegrates due to removal of the organic amine template.     

Bi3.25La0.75Ti3O12纳米线的可见光催化性能

研究了用一步水热法制备的掺镧钛酸铋(Bi_3.25La_0.75Ti₃O₁₂, BLT)纳米线的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. 结果表明, 制备的纳米线为纯相的Bi_3.25La_0.75Ti₃O₁₂, 平均直径约为25 nm. 室温光致发光谱(PL)显示BLT纳米线在433和565 nm附近有较强的发射峰, 分别对应激子发射和表面缺陷发光. 紫外-可见漫反射光谱(UV-Vis DRS)表明BLT样品的带隙能约为2.07 eV. 利用可见光(λ>420 nm)照射下的甲基橙降解实验评价了BLT样品的光催化性能. 结果表明, BLT的光催化活性比商用TiO₂催化剂P25、掺氮TiO₂和纯相钛酸铋(Bi₄Ti₃O₁₂, BIT)高得多. BLT光催化剂具有更高催化活性的原因是La³⁺离子掺杂拓展了BIT对可见光的吸收范围, 同时抑制了BIT的光生电子-空穴的复合.     

A novel route to perovskite lead titanate from lead and titanium glycolates via the sol–gel process

Pure perovskite lead titanate powder (PbTiO₃) is successfully produced via the sol–gel process using lead and titanium glycolates as starting precursors and has been synthesized by the oxide one spot synthesis process. The obtained lead titanate is of the tetragonal form of the perovskite phase, with high purity and nearly zero moisture content. From high‐resolution mass spectra, the XRD technique, Raman‐FTIR and TGA‐DTA analysis, the lead–titanium glycolates undergo sol–gel transition through the formation of Pb? O? Ti bonds. From the SEM micrographs, the PbTiO₃ particle shape transforms from an agglomerate sphere to a needle and fiber‐like shapes as the calcination temperature is varied above T_c. The corresponding molecular structural transformation, from the tetragonal form to the cubic form, occurs at 430 °C. The lead titanate powder calcined at 300 °C for 3 h has the highest dielectric constant and electrical conductivity values, namely 17470 and 1.83 × 10^?3, respectively. Copyright © 2006 John Wiley & Sons, Ltd.     

Long Fe3O4 nanowires decorated by CdTe quantum dots: Synthesis and magnetic-optical properties

This work describes the synthesis and magnetic-optical properties of Fe₃O₄ nanowires decorated by CdTe quantum dots. The composite nanowires with a length of 1 μm and an average diameter of 23±3 nm were prepared in a high yield through the preferential growth of Fe₃O₄ on CdTe quantum dots using ethylenediamine as template. Their growth mechanism was discussed based on the results of control experiments. Studies on the optical and magnetic properties of the composite nanowires reveal that they assume not only yellow-green emission feature but also room temperature ferromagnetism.     

Crystallization of textured PbTiO3 films deposited from gels

Sol-gel processed PbTiO₃ thin films have been deposited by spin coating onto different subtrates; Si[111], Si/Al, Si/SiO₂/Cr/Pt, MgO[100], SrTiO₃[100] and sapphire. Interactions between the substrate and PbTiO₃ films after heat treatment have been studied by X-ray diffraction and Rutherford Back Scattering. When deposited onto sapphire and Si[111], PbTiO₃ films exhibit a preferred orientation with (101) perpendicular to the substrate. These films become oriented along (100) onto MgO and (001) onto SrTiO₃[100] substrates. A strong channelling effect is observed by the RBS technique when the film is oriented along the c axis on SrTiO₃[100] suggesting that these films are epitaxially grown. The diffusion of metal atoms during the thermal treatment gives rise to the formation of lead silicate on Si[111] substrates. As a result a pyrochlore phase is formed. Lead titanate films on Si/SiO₂/Cr/Pt and Si/Al substrates are polycrystalline and do not exhibit any texture.     

N2流量对GaN的形貌及光学和电学性能的影响

采用化学气相沉积法(CVD)在Si(100)衬底上以Ni为催化剂, 金属Ga和NH₃为原料合成了GaN微纳米结构, 并研究了N₂流量对产物GaN的形貌及光学和电学性能的影响。利用场发射扫描电子显微镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、X-ray能谱仪(EDS)、光致发光谱(PL)和霍尔效应测试仪(HMS-3000)等测试手段对样品的形貌、结构、成分、光学和电学性能进行了分析。结果表明, 随着N₂流量的增加, 产物GaN的形貌发生了由微米棒到蠕虫状线再到光滑纳米线的转变;生成的GaN均为六方纤锌矿结构;样品均表现出383 nm的近带边紫外发射峰和470 nm左右的蓝光发射峰;所有样品均为n型;并对产物GaN的形貌转变机理进行了分析。     

N2流量对GaN的形貌及光学和电学性能的影响

采用化学气相沉积法(CVD)在Si(100)衬底上以Ni为催化剂,金属Ga和NH3为原料合成了GaN微纳米结构,并研究了N2流量对产物GaN的形貌及光学和电学性能的影响。利用场发射扫描电子显微镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、Xray能谱仪(EDS)、光致发光谱(PL)和霍尔效应测试仪(HMS-3000)等测试手段对样品的形貌、结构、成分、光学和电学性能进行了分析。结果表明,随着N2流量的增加,产物GaN的形貌发生了由微米棒到蠕虫状线再到光滑纳米线的转变;生成的GaN均为六方纤锌矿结构;样品均表现出383 nm的近带边紫外发射峰和470 nm左右的蓝光发射峰;所有样品均为p型;并对产物GaN的形貌转变机理进行了分析。     

Distinguishing metal halide molecular clusters from perovskite magic sized clusters in the synthesis of metal halide perovskite nanostructures

Background

Research into perovskite nanocrystals (PNCs) has uncovered interesting properties compared to their bulk counterparts, including tunable optical properties due to size-dependent quantum confinement effect (QCE). More recently, smaller PNCs with even stronger QCE have been discovered, such as perovskite magic sized clusters (PMSCs) and ligand passivated PbX₂ metal halide molecular clusters (MHMCs) analogous to perovskites.

Objective

This review aims to present recent data comparing and contrasting the optical and structural properties of PQDs, PMSCs, and MHMCs, where CsPbBr₃ PQDs have first excitonic absorption around 520 nm, the corresponding PMSCS have absorption around 420 nm, and ligand passivated MHMCs absorb around 400 nm.

Results

Compared to normal perovskite quantum dots (PQDs), these clusters exhibit both a much bluer optical absorption and emission and larger surface-to-volume (S/V) ratio. Due to their larger S/V ratio, the clusters tend to have more surface defects that require more effective passivation for stability.

Conclusion

Recent study of novel clusters has led to better understanding of their properties. The sharper optical bands of clusters indicate relatively narrow or single size distribution, which, in conjunction with their blue absorption and emission, makes them potentially attractive for applications in fields such as blue single photon emission.     

Hydrothermal synthesis of monodisperse Fe3O4 nanoparticles based on modulation of tartaric acid

In this paper, monodisperse Fe₃O₄ nanoparticles with single crystalline structure were synthesized via a facile environment-friendly method. And the size of the nanoparticles ranges from 10 nm to 15 nm. As-synthesized Fe₃O₄ were characterized by X-ray diffraction instrument (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrometer and field emission transmission electron microscope (FE-TEM). The effect of tartaric acid (TA) amount on products was investigated by XRD and TEM. The results indicated that TA could commendably modulate the crystalline phase, morphology and size of nanometer Fe₃O_4. A possible generated mechanism of Fe₃O₄ crystals was proposed in virtue of UV–vis absorption spectra. Besides, the magnetic properties of as-synthesized Fe₃O₄ were detected.     

Synthesis,Ferroelectric and Optical Properties of (Pb,Ca)TiO3 Thin Films by Soft Solution Processing

Calcium modified lead titanate sol was synthesized using a soft solution processing, the so-called polymeric precursor method. In soft chemistry method, soluble precursors such as lead acetate trihydrate, calcium carbonate and titanium isopropoxide, as starting materials, were mixed in aqueous solution. Pb_0.7Ca_0.3TiO₃ thin films were deposited on platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure, dielectric and optical properties of the thin films were investigated. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 299 and 0.065, respectively, for a thin film with 230 nm thickness annealed at 600°C for 2 h. The remanent polarization (2P_r) and coercive field (E _c) were 32 C/cm² and 100 kV/cm, respectively. Transmission spectra were recorded and from them, refractive index, extinction coefficient, and band gap energy were calculated. Thin films exhibited good optical transmissivity, and had optical direct transitions. The present study confirms the validity of the DiDomenico model for the interband transition, with a single electronic oscillator at 6.858 eV. The optical dispersion behavior of PCT thin film was found to fit well the Sellmeir dispersion equation. The band gap energy of the thin film, annealed at 600°C, was 3.56 eV. The results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of PCT thin films.     

一维纳米材料Cs0.2WO3和W18O49长度与红外吸收关联性的Mie散射理论推导及实验验证

研究表明二元、三元钨基氧化物的红外吸收性能具有尺寸和形貌依赖性,但还没有普适性的物理学机理及计算方法。本工作基于Mie散射理论,推导了一维材料的长度与光吸收性能之间的关系,通过理论推导计算和实验验证,探究了纳米钨基氧化物的红外吸收性能与颗粒长度的关联性。首先,基于Mie散射理论的推演和计算,揭示了增加纳米Cs_(0.2)WO_3和W_(18)O_(49)材料长度可适度提高其近红外吸收性能的规律。其次,测试了合成的不同长度Cs_(0.2)WO_3纳米棒和W_(18)O_(49)纳米线的红外吸收性能,结果与理论计算及模拟相吻合。其中在2 500～20 000 nm波长范围内Cs_(0.2)WO_3纳米棒和W_(18)O_(49)纳米线随长度的变化趋势不同,Cs_(0.2)WO_3纳米棒的红外吸收性能随长度的增加而增加,而W_(18)O_(49)纳米线的红外吸收性能随长度的增加而减弱。Cs_(0.2)WO_3纳米棒和W_(18)0O_9纳米线的光热效应均随长度的增加而增加,增幅分别达18.5%和12.7%,再次验证了长度效应。     

Chloro-free route to mixed-metal oxides. Synthesis of lead titanate nanoparticles from a single-source precursor route

A new heterobimetallic nitrilotriacetatoperoxotitanate complex of titanium and lead [Pb(H₂O)₃]₂[Ti₂(O₂)₂O(nta)₂]·4H₂O (C₆H₆O₆N=H₃nta) was isolated in pure crystals directly from the solution containing tetrabutyl orthotitanate, hydrogen peroxoide, lead acetate, and nitrilotriacetic acid at pH = 2.0–4.0. The isolated complex was characterized by elemental analyses, IR spectrum, thermal analysis (TG), and single-crystal X-ray diffraction. The single-crystal X-ray structural analysis revealed that the titanium atom is N,O,O′,O′′-chelated by the nitrilotriacetate and O,O′-chelated by the peroxo group and was coordinated to the bridging O atom in an overall pentagonal-bipyramidal geometry. The thermal decomposition of this precursor led to the formation of phase-pure lead titanate (PbTiO₃) at ≥450 °C. The morphology, microstructure, and crystalline of the resulting PbTiO₃ product have been characterized by BET, transmission electron microscopy, and powder X-ray diffraction. The TEM micrographs revealed that the size of the as-synthesized crystallines to be 50–100 nm range. The BET measurement revealed that the PbTiO₃ powders had a surface area of 5.6 m²/g.     

Size effect of added LaB6 particles on optical properties of LaB6/Polymer composites

Modified LaB₆ particles with sizes ranging from 50 nm to 400 nm were added into polymethyl methacrylate (PMMA) matrix in order to investigate the effect of added LaB₆ particles on optical properties of LaB₆/PMMA composites. Method of in-situ polymerization was applied to prepare PMMA from raw material—methyl methacrylate (MMA), a process during which LaB₆ particles were dispersed in MMA. Ultraviolet-visible-near infrared (UV-vis-NIR) absorption spectrum was used to study optical properties of the as-prepared materials. The difference in particle size could apparently affect the composites' absorption of visible light around wavelength of 600 nm. Added LaB₆ particles with size of about 70 nm resulted in the best optical properties among these groups of composites.     

Optical and thermal properties of unsymmetrical liquid crystalline compounds based on isoxazole

The thermal and optical properties of two series of unsymmetrical liquid crystalline compounds based on an isoxazole ring are described. Of these materials, 3–7 and 8–12 displayed strong absorption at 285 nm and a weak blue fluorescence in solution at around 377 nm, even with the presence of a high conjugated core. The fluorescence quantum yields observed varied from low to moderate (Φ _F ?=?1–62%), with large Stokes shifts (60–178 nm). All compounds exhibited liquid crystalline behaviour with a wide mesomorphism temperature range and characteristic phases of calamitic compounds, among them smectic A (SmA), smectic C (SmC) and nematic (N) phases. Their phases were characterised using polarising optical microscopy and differential scanning calorimetry. In addition, with X-ray diffraction experiments, layer spacing of 33.3–40.0 Å were observed for the smectic phases.     

Bi3.25Sm0.75Ti3O12纳米线的水热合成及可见光催化性能

用一步水热法制备了直径约为40 nm的Bi3.25Sm0.75Ti3O12(BSmT)纳米线。BSmT纳米线为层状钙钛矿结构。紫外可见漫反射光谱表明,制备出的BSmT材料的带隙能约为2.67 eV。催化反应结果表明,BSmT的光催化活性比掺氮TiO2(N-TiO2)和纯相钛酸铋(Bi4Ti3O12,BIT)高得多,经可见光照射360 min,浓度为0.01 mmol.L-1甲基橙溶液的降解率可达到92.0%。BSmT光催化剂具有更高催化活性的原因是Sm3+离子掺杂拓展了BIT对可见光的吸收范围,同时抑制了BIT的光生电子-空穴的复合。并且BSmT光催化剂经循环使用4次后,其光催化活性并没有明显降低,表明BSmT是一种稳定有效的可见光催化剂。