Synthesis of Humin-based Carbon Quantum Dots and Luminescent Properties

The unique properties of carbon quantum dots(CQDs) make them promising materials in many fields. Herein, we present a facile method for the preparation of photo-luminescent CQDs using humins as the carbon precursor for the purpose of providing a high value-added solution for this "biomass conversion process waste". The structure of the CQDs was analyzed, and the effects of reaction temperature and time on the CQDs' fluorescence were investigated. The results showed that humins were effectively carbonized during the reaction. The fluorescence intensity of humin-based CQDs initially increased with reaction temperature and time, and subsequently decreased beyond 200℃ and 4 h. Polyaromatic structures and hydrophilic groups such as O—H, C—O, —COOH and C==O groups exist in the CQDs. The huminbased CQDs have the dimension of 3～7 nm with an average size of about 5.5 nm. The highest emission intensity of blue/cyan fluorescence light at 440 nm is achieved on the excitation with UV light at the wavelength of 330 nm.     

一种激光诱导灼蚀制备纳米硅的新方法

采用高强度激光灼蚀沉积(PLD)的方式,在流动N2做为保护气体的情况下,成功制备出Si纳米结构,并利用扫描电镜(SEM)、光致发光(PL)进行表征。结果表明,该方法制备的纳米Si尺寸在几nm到几10nm之间,同时它具有较强的发光,发光强度比同等测量条件下的多孔Si(PS)样品高10倍以上,而且方法比较简单。     

Luminescent and photocatalytic properties of hollow SnO2 nanospheres

Size tunable solid SnO₂ (STO) and hollow SnO₂ (HTO) nanospheres were prepared by a sacrificing template method. The peaks around 390 nm were observed in photoluminescence (PL) spectra. Based on the results, the PL intensity exhibits morphology-dependence and size-dependence, and HTO structure displays better optical properties than STO structure. The degradation of Methyl Orange (MO) in aqueous solution is selected as a probe reaction to evaluate the catalytic activity of nano-SnO₂. The result shows that HTO structure presents stronger photocatalytic (PC) activity. According to the result of specific surface area testing, the improved PL and PC properties of HTO structure can be mainly explained by the surface effect induced by large specific surface area. This work is meaningful for developing nanomaterials with enhanced optical and photochemical properties.     

Direct vapor phase growth process and robust photoluminescence properties of large area MoS2 layers

There has been growing research interest in the use of molybdenum disulfide in the fields of optoelectronics and energy harvesting devices, by virtue of its indirect-to-direct band gap tunability. However, obtaining large area thin films of MoS2 for future device applications still remains a challenge. In the present study, the amounts of the precursors （S and MOO3） were varied systematically in order to optimize the growth of highly crystalline and large area MoS2 layers by the chemical vapor deposition method. Careful control of the amounts of precursors was found to the key factor in the synthesis of large area highly crystalline flakes. The thickness of the layers was confirmed by Raman spectroscopy and atomic force microscopy. The optical properties and chemical composition were studied by photoluminescence （PL） and X-ray photoelectron spectroscopy. The emergence of strong direct excitonic emissions at 1.82 eV （A-exciton, with a normalized PL intensity of -55 × 10^3） and 1.98 eV （B-exciton, with a normalized PL intensity of -5 × 10^3） of the sample at room temperature clearly indicates the high luminescence quantum efficiency. The mobility of the films was found to be 0.09 cm^2/（V.s） at room temperature. This study provides a method for the controlled synthesis of high-quality two-dimensional （2D） transition metal dichalcogenide materials, useful for applications in nanodevices, optoelectronics and solar energv conversion.     

含有均二苯乙烯基的苯并二口恶唑衍生物的合成及荧光特性

引言 目前人们已发现许多均二苯乙烯衍生物具有蓝色发光的特性[1-2],此类有机共轭小分子作为空穴型光电发光材料的共轭化学结构已确定并且发光色度纯,两个苯环上引入取代基对其发光波长和光量子效率还有调节作用,合成方法也比较简单[3-4].     

Exciton photo-luminescence of GaN bulk crystals grown by the AMMONO method

GaN in form of microcrystals were obtained using a new technique—the AMMONO method. The growth was performed at relatively low temperature and pressure conditions, in comparison with other techniques used for GaN growth. The AMMONO crystals were of pure hexagonal phase and had a low electron concentration of about 5×10¹⁵ cm⁻³. Their luminescence was very intensive and homogenous. At helium temperatures exciton recombinations of record narrow lines (FWHM down to 1 meV) dominated the luminescence spectra. Energy positions of the exciton lines did not depend on excited microcrystals which confirmed they were strain-free.     

Some new organic–inorganic hybrid semiconductors based on metal halide units: structural,optical and related properties†

The structural, optical and related properties of organic–inorganic hybrid semiconductors based on the organic molecules (cations) CH₃NH₃, H₃N(CH₂)₆NH₃, C₆H₅CH₂NH₃, CH₃C₆H₄CH₂NH₃, CH₃OC₆H₄CH₂CH₂NH₃, (H₂N)₂CS(CH₂)₄SC(NH₂)₂, H₃NCH₂CH₂OCH₂CH₂NH₃, C₆H₅CH₂CH₂SC(NH₂)₂, C₁₀H₂₁SC(NH₂)₂, O₂NC₆H₄CH₂SC(NH₂)₂, 1-naphthylmethylammonium C₁₀H₇CH₂NH₃, 9-anthrylmethylammonium C₁₄H₉CH₂NH₃ and 1-pyrenylmethylammonium C₁₆H₉CH₂NH₃ and the inorganic units MX_n (anions) (M≡Bi, Sb, Sn, Pb, Cu, Ag; X≡I, Br, Cl) are described. There is evidence that the position, intensity and shape of the excitonic bands depend on the order/disorder of the inorganic component and on the electronic interaction between organic and inorganic components. Copyright © 2000 John Wiley & Sons, Ltd.