We develop high efficiency solution-processed pure green organic light-emitting devices using a starburst molecule 7,7′,7″-(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene-2,7,12-triyl)tris(4-(4-(9H-carbazol-9-yl)phenyl)benzo[c][1,2,5]thiadiazole)(TRcz)doped 2-methyl-9,10-di(2-naphthyl)anthracene(MADN)as the emitting layers.The electroluminescence properties of the devices with different doping concentrations are investigated.With the increasing doping concentration from 0.5wt%to 5wt%,the maximum efficiency changes from 4.8cd/A to 8.4cd/A.Under the optimal concentration of 4wt%,the device shows pure green emission at 516nm with a chromaticity coordinate of(0.30,0.59)as well as a high brightness of 19900cd/m^(2)and a high efficiency of 10.1cd/A,which are better than 11490cd/m^(2)and 4.2cd/A obtained in the undoped device.
The effect of Au nanorods(NRs) on optical-to-electric conversion efficiency is investigated in inverted polymer solar cells, in which Au NRs are sandwiched between two layers of Zn O. Accompanied by the optimization of thickness of Zn O covered on Au NRs, a high-power conversion efficiency of 3.60% and an enhanced short-circuit current density(J SC) of10.87 m A/cm2 are achieved in the poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester(P3HT:PC60BM)-based inverted cell and the power conversion efficiency(PCE) is enhanced by 19.6% compared with the control device. The detailed analyses of the light absorption characteristics, the simulated scattering induced by Au NRs, and the electromagnetic field around Au NRs show that the absorption improvement in the photoactive layer due to the light scattering from the longitudinal axis and the near-field increase around Au NRs induced by localized surface plasmon resonance plays a key role in enhancing the performances.
A simple and effective method for the preparation of amphiphilic graphene(AG)is presented under an organic solvent-free synthetic condition.The synthetic route first involves a cyclization reaction between carboxylic groups on graphene oxide and the amino groups on 5,6-diaminopyrazine-2,3-dicarbonitrile,and subsequent reduction by hydrazine.Results of UV-vis spectroscopy,Fourier transformed infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA)and Raman spectroscopy have confirmed that the covalent functionalization of graphene can be achieved through the formation of imidazo[4,5-b]pyrazine on the graphene sheets.As a result,AG can be successfully dispersed in water and common organic solvents.This work successfully provides a facile and efficient way to fabricate AG and may extend the potential applications of graphene-based materials in nanoelectronic devices,polymer fillers and biological field.
Three metal-organic frameworks,{[Mg_2(MFDA)_2(DMF)_3]·0.5H_2O}_n(1),{[Ca(MFDA)(DMF)(H_2O)]·0.5DMF}_n(2)and[Ca(MFDA)(DMF)_2]_n(3)(DMF=N,N-dimethylformamide)have been synthesized by the solvothermal reactions between the ligand 9,9-dimethylfluorene-2,7-dicarboxylic acid(H_2MFDA)and the corresponding metal salts,respectively.The single crystal X-ray structural analyses reveal that compounds 1-3 display three-dimensional structures based on the M(Ⅱ)-O-C chains.It is interesting that the MFDA ligands in 1-3 have different dihedral angles between the two carboxylate groups ranging from 9.9(1)°to 41.8(2)°.All of compounds exhibit strong ligand-centered blue emissions under UV lights.Their thermal properties have also been studied.
Three isostructural three-dimensional(3D) lanthanide-based metal-organic frameworks [Ln_2L(H_2L)(NMP)_2].H_2O(Ln=Sm(1), Eu(2), Gd(3); H_4L=1,1′:4′,1″-terphenyl-2′,4,4″,5′-tetracarboxylic acid; NMP=N-methyl-2-pyrrolidone) have been synthesized and structurally characterized. In 1–3, two Ln3+ ions are doubly-bridged by two oxygen atoms of two carboxylate groups to form the dinuclear Ln_2(OCOO–)_2 unit. Each Ln_2(OCOO–)_2 unit links with four H_2L^(2-) ligands and four L4. ligands to lead to the 3D framework,which can be rationalized as a new trinodal 4,4,8-connected(44.62)(45.6)(412.616) topological network by considering the dinuclear Ln_2(OCOO–)_2 units as 8-connected nodes and L^4./H_2L^(2-) ligands as planar 4-connected nodes, respectively. 1 and 3 exhibit blue emission originated from the ligand with the emission maximum at 384 nm, while 2 shows intense characteristic red emission of Eu^(3+) ions and weak ligand-centered emission. Moreover, 2 has fluorescent quenching response towards the aromatic nitro compounds, especially for the 3,4-dinitrotoluene(3,4-DNT) with the linear Stern-Volmer relationship in the concentration range of 0–1 mM and the quenching constant(Ksv) of 2.084×10~3 M^(-1).
Cupric oxide(CuO)nanoparticles were grown on zinc oxide(ZnO)nanorod(NR)arrays to form ZnO–CuO corn-like composites via a simple two step solution-based method.First,ZnO nanorods were grown on a glass substrate by the hydrothermal method.Afterwards,CuO crystals were photochemically deposited on ZnO NRs using ultraviolet(UV)light irradiation at room temperature.The density and size of CuO nanoparticles(NPs)on ZnO NRs can be controlled by the irradiation time of UV light.The structural and optical properties of ZnO–CuO nanocomposites were characterized by using various techniques such as UV-vis absorption spectroscopy,photoluminescence,scanning electron microscopy,energy dispersive x-ray spectroscopy,and x-ray diffraction.ZnO–CuO nanocomposites show an excellent improvement in photocatalytic characteristics compared to bare ZnO NRs.
Strong light-matter interactions involved with photons and quasiparticles are fundamentally interesting to access the wealthy many-body physics in quantum mechanics.The emerging two-dimensional(2D)semiconductors with large exciton binding energies and strong quantum confinement allow to investigate exciton-photon coupling at elevated temperatures.Here we report room-temperature formation of Bragg polaritons in monolayer semiconductor on a dielectric mirror through the exciton-Bragg photon coupling.With the negative detuning energy of -30 meV,angle-resolved reflection signals reveal anti-crossing behaviors of lower and upper polariton branches at±18°together with the Rabi splitting of 10 meV.Meanwhile,the strengthened photoluminescence appears in the lower polariton branch right below the anti-crossing angles,indicating the presence of the characteristic bottleneck effect caused by the slowing exciton-polariton energy relaxation towards the band minimum.The extracted coupling strength is between the ones of weak and distinct strong coupling regimes,where the eigenenergy splitting induced by the moderate coupling is resolvable but not large enough to fully separate two polaritonic components.Our work develops a simplified strategy to generate exciton-polaritons in 2D semiconductors and can be further extended to probe the intriguing bosonic characteristics of these quasiparticles,such as Bose-Einstein condensation,polariton lasing and superfluidity,directly at the material surfaces.
