Harvesting vibrations via 3D phononic isolators

We report on the existence of unidirectional phononic band gaps that may span over extended regions of the Brillouin zone and can find application in trapping elastic (acoustic) waves in properly designed multilayered 3D structures. Phononic isolators operate as a result of asymmetrical wave transmission through a slab of a crystallographic phononic structure with broken mirror symmetry. Due to the use of lossless materials in the crystal, the absorption rate is dramatically enhanced when the proposed isolator is placed next to a vibrational harvesting cell.     

Greener approach toward synthesis of biologically active s-Triazine (TCT) derivatives: A recent update

The greener methodology to synthesize s-triazine derivatives (also known as TCT) is described, including synthesis through microwave, ultrasound, and solvent-free conditions. This review mainly focuses on reactions of TCT (2,4,6-trichloro-1,3,5-triazine) with various substituents having amine and hydroxy functionalities to give corresponding triazine derivatives under a greener approach. The results of reactions indicate that, unlike classical methods, green methods result in better yields of the product, through a rapid reaction, under mild reaction conditions, and by easy workup procedures.     

The Impact of C2 Insertion into a Carbazole Donor on the Physicochemical Properties of Dibenzo[a,j]phenazine-Cored Donor–Acceptor–Donor Triads

Novel electron donor–acceptor–donor (D-A-D) compounds comprising dibenzo[a,j]phenazine as the central acceptor core and two 7-membered diarylamines (iminodibenzyl and iminostilbene) as the donors have been designed and synthesized. Investigation of their physicochemical properties revealed the impact of C₂ insertion into well-known carbazole electron donors on the properties of previously reported twisted dibenzo[a,j]phenazine-core D-A-D triads. Slight structural modification caused a drastic change in conformational preference, allowing unique photophysical behavior of dual emission derived from room-temperature phosphorescence and triplet–triplet annihilation. Furthermore, electrochemical analysis suggested sigma-dimer formation and electrochemical polymerization on the electrode. Quantum chemical calculations also rationalized the experimental results.     

用于宽谱带发射白色发光二极管的黄色荧光粉Sr8MgAl(PO4)7∶xEu2+的制备及发光性能

通过高温固相反应合成了一系列宽谱带发射黄色荧光粉Sr_8MgAl(PO_4)_7∶x Eu~(2+)(SMAP∶x Eu~(2+)),并对其物质结构、发光性能及其在白色发光二极管(WLED)领域的应用进行了探究。X射线衍射(XRD)测试结果表明,SMAP∶x Eu~(2+)系列荧光粉具有单斜结构和C2/m空间群,激活剂Eu~(2+)离子能够很好地进入SMAP基质中并占据Sr~(2+)离子的晶格位点。漫反射光谱分析显示SMAP基质属于宽带隙材料,带隙宽度为3.60 e V。此外,SMAP∶x Eu~(2+)具有较宽的激发范围(280～500 nm),对应于Eu~(2+)离子的4f~7→4f~65d~1跃迁;在380 nm近紫外光激发下,呈现出450～800 nm的多发光中心的非对称黄光发射,发射峰位于590 nm处。基于高斯多峰拟合结果,得到3个发光中心,分别位于528、600和680 nm。最后,将已制备的黄色荧光粉SMAP∶0.05Eu~(2+)与商业化蓝粉Ba Mg Al_(10)O_(17)∶Eu~(2+)混合涂覆到400 nm芯片上制得色温较好(3 344 K)、显色指数较高(90.1)的WLED。     

利用固体物理LED发光原理测量普朗克常数

普朗克常数是物理学中一个重要的常数,利用二极管的量子特性探讨运用发光二极管来测量普朗克常数。通过测量二极管的伏安曲线,确定其阈值电压,根据相关量子理论,间接得出普朗克常数,通过与光电效应法测量普朗克常数的测量结果相比较,结果表明此误差略大,但作为一种新型的实验方法探索,对于开拓学生的综合素养还是非常有益的。     

A novel red-emitting phosphor Ca9Bi(PO4)7:Eu3+ for near ultraviolet white light-emitting diodes

Red phosphors Ca₉Bi_1-x(PO₄)₇:xEu³⁺ (x = 0.06, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 and 1.00) were synthesized by a conventional solid-state reaction (SSR) route. The X-ray diffraction patterns, photoluminescence spectra, ultraviolet–visible reflection spectroscopy, decay time and the International Commission on Illumination (CIE) chromaticity coordinates of these compounds were characterized and analyzed. The Eu-doped Ca₉Bi(PO₄)₇ phosphors exhibited strong red luminescence which peaks located at 615 nm due to the ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺ ions after excitation at 393 nm. Ultraviolet–visible spectra indicated that the band-gap of Ca₉Bi_0.30(PO₄)₇:0.70Eu³⁺ is larger than that of Ca₉Bi(PO₄)₇. The results indicate that the phosphor Ca₉Bi_0.30(PO₄)₇:0.70Eu³⁺ can be a suitable red-emitting phosphor candidate for LEDs.     

The beneficial effects of a p-type GaInN spacer layer on the efficiency of GaInN/GaN light-emitting diodes

Light-emitting diodes (LEDs) with a Mg-doped p-type Ga_1−xIn_xN (0 ≤ x ≤ 0.07) spacer layer located between an undoped GaN spacer layer and the electron blocking layer are investigated. The LEDs are found to have comparable peak efficiency but less efficiency droop when the crystal quality of the p-type Ga_1−xIn_xN spacer layer is well-controlled by lowering the growth temperature and by using a suitable In composition and Mg doping concentration. All LED samples with the p-type spacer layer show a smaller efficiency droop compared to a reference LED having an undoped GaN spacer. Among the sample sets investigated, an optical power enhancement of 12% at 111 A/cm² is obtained when inserting a 5 nm-thick p-type Ga_0.97In_0.03N spacer layer. The results support that carrier transport is the key factor in the efficiency droop observed in GaN-based LEDs.     

2,2,2‐Trifluoroacetophenone as an Organocatalyst for the Oxidation of Tertiary Amines and Azines to N‐Oxides

A cheap, mild and environmentally friendly oxidation of tertiary amines and azines to the corresponding N‐oxides is reported by using polyfluoroalkyl ketones as efficient organocatalysts. 2,2,2‐Trifluoroacetophenone was identified as the optimum catalyst for the oxidation of aliphatic tertiary amines and azines. This oxidation is chemoselective and proceeds in high‐to‐quantitative yields utilizing 10 mol % of the catalyst and H₂O₂ as the oxidant.     

Uncatalyzed Hydroamination of Electrophilic Organometallic Alkynes: Fundamental,Theoretical, and Applied Aspects

Simple reactions of the most used functional groups allowing two molecular fragments to link under mild, sustainable conditions are among the crucial tools of molecular chemistry with multiple applications in materials science, nanomedicine, and organic synthesis as already exemplified by peptide synthesis and “click” chemistry. We are concerned with redox organometallic compounds that can potentially be used as biosensors and redox catalysts and report an uncatalyzed reaction between primary and secondary amines with organometallic electrophilic alkynes that is free of side products and fully “green”. A strategy is first proposed to synthesize alkynyl organometallic precursors upon addition of electrophilic aromatic ligands of cationic complexes followed by endo hydride abstraction. Electrophilic alkynylated cyclopentadienyl or arene ligands of Fe, Ru, and Co complexes subsequently react with amines to yield trans‐enamines that are conjugated with the organometallic group. The difference in reactivities of the various complexes is rationalized from the two‐step reaction mechanism that was elucidated through DFT calculations. Applications are illustrated by the facile reaction of ethynylcobalticenium hexafluorophosphate with aminated silica nanoparticles. Spectroscopic, nonlinear‐optical and electrochemical data, as well as DFT and TDDFT calculations, indicate a strong push–pull conjugation in these cobalticenium– and Fe– and Ru–arene–enamine complexes due to planarity or near‐planarity between the organometallic and trans‐enamine groups involving fulvalene iminium and cyclohexadienylidene iminium mesomeric forms.