Effect of the thickness of Bi2Se3 sheets on the morphologies of Bi2Se3–ZnS nanocomposites and improved photoresponsive characteristic

Bi₂Se₃–ZnS nanocomposites were synthesized with different morphologies and their photoluminescence were investigated. The compounds formed hexagonal rods as the thickness of Bi₂Se₃ sheets stayed about a few nanometers; while the Bi₂Se₃ sheets’ thickness increased to tens of nanometers, the compounds formed novel morphologies of Bi₂Se₃–ZnS nanocomposites with small ZnS nanoparticles randomly decorated onto Bi₂Se₃ sheets. The formation mechanism was proposed based on the different thickness of Bi₂Se₃ sheets used in experimental processes. In addition, the significant fluorescence quench and obvious improvement in photoresponsive characteristic were shown after the integration of ZnS with Bi₂Se₃ sheets, which showed potential application in optoelectronic devices.     

Synthesis and characterization of novel 2,7-carbazole derivatives for blue light-emitting diodes

Two 2,7-carbazole based low molecular weight derivatives, 9-hexyl-N ²,N ²,N ⁷,N ⁷-tetraphenyl-carbazole-2,7-diamine (TPCA) and 9′-hexyl-9′H-9,2′:7′,9″-tercarbazole (HTC), were synthesized by Buchwald and Ullmann coupling reactions, respectively. The optical, electrochemical and thermal properties of this two analogous small molecule hosts have been characterized. The HOMO level of TPCA and HTC were ?5.25 and ?5.29 eV indicating good hole-transporting properties. Both of the compounds emit deep blue light peaked at 410 and 428 nm in solid state. According to the measurement, the luminescence quantum yield of TPCA is 0.98, almost 1.7 times higher than that of HTC (0.59) in dilute THF solution. The geometrical and electronic properties of the compounds were studied using density functional theory calculations. The studies mentioned above indicate that both TPCA and HTC are suitable for active materials of blue light-emitting diodes.     

Synthesis and characterisation of MoS2 quantum dots by liquid nitrogen quenching

Among transition metal dichalcogenides family, molybdenum disulphide (MoS₂) nanomaterial has a vital role in two-dimensional field due to its intrinsic optical and electronic properties. In this study, we report a new top-down approach for synthesising MoS₂ quantum dots (QDs). This strategy consists of liquid nitrogen (LN2) quenching of bulk MoS₂ material followed by two processes, probe sonication and ultra-centrifugation. This approach is simple, cost effective and eco-friendly. The structural, optical and morphological properties of obtained MoS₂ quantum dots were characterised. Photoluminescence spectra (PL) of the synthesised MoS₂ QDs show blue light emission when excited with ultraviolet radiation (365?nm). A significant observation in this study is that, the peak position of photoluminescence (PL) emission spectra is independent of excitation wavelength. In addition, a higher fluorescence quantum yield was obtained for the present MoS₂ QDs compared to MoS₂ QDs prepared by other methods.     

Photoluminescence of epoxy resin modified by carbazole and its halogen derivative at 82 K

The spectra and relative quantum yield of fluorescence and phosphorescence were measured for 9-(2,3-epoxypropyl)carbazole (EPK) added to epoxy resin (R) (R₅EPK – 5% weight content of the carbazole group in a polymer) and its mono and dihalogen derivative (Cl and Br). The materials under study have excellent mechanical properties. At 82 K photoluminescence (PL) spectra of these materials are composed of fluorescence (FL) and phosphorescence (PH) components while at 280 K, PH component is not observed. The vibrational frequencies of fluorescence and phosphorescence for R₅EPK were determined using Gaussian deconvolution. A decrease in the fluorescence and an increase in the phosphorescence quantum efficiency were observed after chemical bonding of heavy atoms Cl and Br.     

Coexistence of interfacial stress and charge transfer in graphene oxide-based magnetic nanocomposites

In this paper, the existence of both compressive stress and charge transfer process in hydrothermally synthesized cobalt ferrite–graphene oxide (CoFe₂O₄/GO) nanocomposites has been established. Transmission electron microscopy results reveal the decoration of CoFe₂O₄ nanoparticles on GO sheets. Magnetic response of nanocomposites was confirmed from superconducting quantum interference device magnetometer measurement. Optical properties of these nanocomposites were investigated by Raman spectroscopy. The interfacial compressive stress involved in this system has been evaluated from observed blue shift of characteristic G peak of graphene oxide. Increase in the full-width half-maximum value as well as upshift in D and G peaks is clear indications of involvement of charge transfer process between GO sheets and dispersed magnetic nanoparticles. The effect of charge transfer process is quantified in terms of shifting of Fermi energy level of these nanocomposites. This is evaluated from variation in contact surface potential difference using scanning Kelvin probe microscopy. XRD spectra of CoFe₂O₄/GO confirm the polycrystalline nature of CoFe₂O₄ nanoparticles. Lattice strain estimated from XRD peaks is correlated with the observed Raman shift.     

Synthesis of carbazole derivatives with high quantum yield and high glass transition temperature

A series of fluorescent compounds derived from carbazole were synthesized via the Wittig–Horner reaction. The compounds had high glass transition temperatures (T_g), in the region of 172–232 °C, and high decomposition temperatures (T_d), ranging from 456 to 491 °C. The derivatives showed very high fluorescence efficiency in solution, with fluorescence quantum yields in the range of 0.88–1.00. The substituent effects on fluorescence emission differed between solution and solid state. In dichloromethane solutions, the substituents had only a minimal effect on the maximum emission wavelength of the compounds with the same bridge.     

Highly fluorescent and biocompatible iridium nanoclusters for cellular imaging

Highly fluorescent iridium nanoclusters were synthesized and investigated its application as a potential intracellular marker. The iridium nanoclusters were prepared with an average size of ~2 nm. Further, these nanoclusters were refluxed with aromatic ligands, such as 2,2′-binaphthol (BINOL) in order to obtain fluorescence properties. The photophysical properties of these bluish-green emitting iridium nanoclusters were well characterized by using UV–Visible, fluorescence and lifetime decay measurements. The emission spectrum for these nanoclusters exhibit three characteristic peaks at 449, 480 and 515 nm. The fluorescence quantum yield of BINOL–Ir NCs were estimated to be 0.36 and the molar extinction co-efficients were in the order of 10⁶ M^?1cm^?1. In vitro cytotoxicity studies in HeLa cells reveal that iridium nanoclusters exhibited good biocompatibility with an IC₅₀ value of ~100 μg/ml and also showed excellent co-localization and distribution throughout the cytoplasm region without entering into the nucleus. This research has opened a new window in developing the iridium nanoparticle based intracellular fluorescent markers and has wide scope to act as biomedical nanocarrier to carry many biological molecules and anticancer drugs.     

Synthesis and optical properties of photochromic perinaphthothioindigo

(1,2-naphtho)(1,8-naphtho)thioindigo (PNT) has been synthesized following a simple Friedel–Crafts route and its photochemical properties in toluene and polymethylmethacrylate (PMMA) have been characterized. PNT is a photochromic molecule capable of reversible photoisomerization between a yellow form (cis-PNT, λ_max = 484 nm) and a purple form (trans-PNT, λ_max = 595 nm). The stable purple form converts to the yellow form with a trans-PNT to cis-PNT conversion quantum yield of 0.027 in toluene and 0.062 in PMMA. The unstable yellow form exhibits a cis-PNT to trans-PNT quantum efficiency of conversion of 0.27–0.85 in toluene and 0.17–0.68 PMMA, with highest conversion efficiency occurring in the vicinity of its λ_max of 484 nm. trans-PNT has a strong fluorescence quantum yield, 0.14 (toluene) and 0.16 (PMMA). For samples prepared photochemically in the cis-PNT form, slow thermal relaxation to the trans form occurs in the dark, with a half life of about 17 h in toluene (25 °C) and even slower, 168 h, in PMMA. The property of photoswitching between fluorescent and non-fluorescent forms makes this material a candidate for many applications in imaging and data storage.     

Novel heterocyclic based blue and green emissive materials for opto-electronics

Two different novel heterocyclic compounds namely 2,5-bis(1,3-diphenyl-4,5-dihydro-1H-pyrazol-5-yl)thiophene (Material I) and 2,5-bis(3-(naphthalen-1-yl)-1-phenyl-4,5-dihydro-1H-pyrazol-5-yl)thiophene (Material II) were designed, synthesized and characterized by spectral methods. The synthesized materials were confirmed by standard techniques such as FT-IR, ¹H NMR and elemental analysis. Physical properties include thermal, surface morphology of the materials were explained from TGA, DSC and SEM analysis. Optical properties such as absorption, emission, solvent effect have been investigated by UV–Visible and fluorescence spectrophotometers. The blue and green emission of the materials was confirmed by using UV light as well as fluorescence spectrophotometers. Bandgap energies of these materials were obtained by both experimental and theoretical calculation from of cyclic voltammetry, UV–Visible spectrophotometer and DFT calculation. I–V characteristic analysis used to determine the threshold voltage (V_on) of the two materials. The obtained results of the materials have promising to be applicable for opto-electronic applications.     

Synthesis and luminescence of ultrafine Er3+- and Yb3+-doped Gd11SiP3O26 and Gd14B6Ge2O34 particles for cancer diagnostics

In search of new contrast materials for NMR and fluorescence diagnostics and neutron capture therapy of cancer, we have synthesized ultrafine Er³⁺- and Yb³⁺-doped Gd₁₁SiP₃O₂₆ and Gd₁₄B₆Ge₂O₃₄ particles and studied their luminescence properties. We measured the Er³⁺ upconversion luminescence spectra of the gadolinium erbium ytterbium phosphosilicates and borate germanates in the visible range and evaluated the absolute quantum yield of their luminescence. The quantum yield of luminescence in the gadolinium phosphosilicate Gd₁₁SiP₃O₂₆ doped with 5.0 at % Yb and 2.5 at % Er is comparable to that in known Yb³⁺/Er³⁺ codoped fluorides. The nonradiative Yb³⁺ ?? Er³⁺ energy transfer efficiency is evaluated.     

Aqueous synthesis of CdSe and CdSe/CdS quantum dots with controllable introduction of Se and S sources

A new and convenient route is developed to synthesize CdSe and core–shell CdSe/CdS quantum dots (QDs) in aqueous solution. CdSe QDs are prepared by introducing H₂Se gas into the aqueous medium containing Cd²⁺ ions. The synthesized CdSe QDs are further capped with CdS to form core–shell CdSe/CdS QDs by reacting with H₂S gas. The gaseous precursors, H₂Se and H₂S, are generated on-line by reducing SeO₃ ^2? with NaBH₄ and the reaction between Na₂S and H₂SO₄, and introduced sequentially into the solution to form CdSe and CdSe/CdS QDs, respectively. The synthesized water-soluble CdSe and CdSe/CdS QDs possess high quantum yield (3 and 20 %) and narrow full-width-at-half-maximum (43 and 38 nm). The synthesis process is easily reproducible with simple apparatus and low-toxic chemicals. The relatively standard deviation of maxima fluorescence intensity is only 2.1 % (n = 7) for CdSe and 3.6 % (n = 7) for CdSe/CdS QDs. This developed route is simple, environmentally friendly and can be readily extended to the large-scale aqueous synthesis of QDs.     

Fabrication and characterization of biodegradable PHBV/SiO2 nanocomposite for thermo‐mechanical and antibacterial applications in food packaging

In the present study, biogenic silica nanoparticles (bSNPs) were synthesized from groundnut shells, and thoroughly characterized to understand its phase, and microstructure properties. The biopolymer was synthesized from yeast Wickerhamomyces anomalus and identified as Poly (3‐hydroxybutyrate‐co ‐3‐hydroxyvalerate) (PHBV) by GC‐MS and NMR analysis. The bSNPs were reinforced to fabricate PHBV/SiO₂ nanocomposites via solution casting technique. The fabricated PHBV/SiO₂ nanocomposites revealed intercalated hybrid interaction between the bSNPs and PHBV matrix through XRD analysis. PHBV/SiO₂ nanocomposites showed significant improvement in physical, chemical, thermo‐mechanical and biodegradation properties as compared to the bare PHBV. The cell viability study revealed excellent biocompatibility against L929 mouse fibroblast cells. The antibacterial activity of PHBV/SiO₂ nanocomposites was found to be progressively improved upon increasing bSNPs concentration against E. coli and S. aureus.Inspec keywords: X‐ray diffraction, microorganisms, antibacterial activity, nanoparticles, cellular biophysics, nanofabrication, silicon compounds, nanocomposites, filled polymers, nanomedicine, biomedical materials, casting, biodegradable materials, food packaging, food safety, biological NMROther keywords: antibacterial applications, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), PHBV matrix, biodegradable PHBV‐SiO₂ nanocomposite, thermomechanical biodegradation properties, biogenic silica nanoparticles, groundnut shells, microstructure properties, biopolymer, yeast Wickerhamomyces anomalus, GC‐MS, NMR analysis, food packaging, intercalated hybrid interaction, XRD analysis, cell viability study, solution casting, SiO₂      

反应时间对CH3NH3PbBr3钙钛矿纳米晶形貌及荧光性能的影响

有机-无机杂化钙钛矿(CH_3NH_3PbX_3,X=Cl、Br、I)材料正成为最近全世界研究的热点,在太阳能电池、量子点发光等众多领域有着广泛的应用。本研究重点考察反应时间对热注入法合成的CH_3NH_3PbX_3纳米晶的形貌及荧光性能的影响,并采用吸收光谱、荧光光谱、X射线衍射、透射电镜及扫描电镜等手段对材料进行分析。研究表明,随着反应时间的延长,产物从6nm左右的球状纳米颗粒变为层状纳米片;反应时间继续延长,纳米片的尺寸变大,厚度变厚;同时,产物的吸收峰和荧光发射峰都发生蓝移。通过绝对量子产率的分析,发现反应时间为180s时产物的量子产率最高。     

Synthesis and optoelectronic properties of thieno[2,3-b]thiophene based bis 1,3,4-oxadiazole derivatives as blue fluorescent material for use in organic light emitting diodes

We report the synthesis and optoelectronic properties of a series of symmetrical disubstituted derivatives containing bis 1,3,4-oxadiazole with thieno[2,3-b]thiophene backbone (3a–f). These novel compounds were synthesized by employing simple and convenient synthetic protocol using thieno[2,3-b]thiphene-2,5,dicarboxylic acid as a starting material. The structures of these target molecules were established by their analytical and spectral data. The photo physical and electrochemical studies revealed that these compounds exhibit good blue fluorescent properties with better quantum yield. These compounds are expected to be of use in various optoelectronic applications.     

Spectroscopic properties and concentration effects on luminescence behavior of Nd doped Zinc–Boro–Bismuthate glasses

A detail investigation on laser spectroscopic properties as a function of Nd³⁺ ions concentration in a new heavy metal oxide based Zinc–Boro–Bismuthate glasses is reported. The Judd–Ofelt analysis indicated an enhancement in Nd–O bond covalency as well as the local asymmetry of active ions on increase in dopant concentration from 0.1 to 1.5 mol%. Based on the Judd–Ofelt intensity parameters, several radiative properties such as transition probability, radiative lifetime, branching ratio and stimulated emission cross-section of Nd³⁺ ions have been derived. The luminescence intensity has showed a strong increase up to 0.5 mol% Nd₂O₃, which then attains maximum at 1 mol% and falls down for further increase in dopant concentration. The luminescence quenching behavior at higher dopant concentration has been attributed to the hopping migration assisted energy transfer mechanism leading to the cross-relaxation among active ions. The energy transfer micro-parameters for cross-relaxation (C_DA) and donor energy migration (C_DD) have been derived from the luminescence decay analysis as well as spectral overlap function respectively. The high stimulated emission cross-section and smaller cross-relaxation micro-parameters along with high quantum yield from the present glasses suggests their potential for compact infrared lasers and waveguide applications.     

Intercalation of alkylammonium ions and oxide layers |TiNbOt|−

The exchange ion properties applied to the oxide HTiNbO₅, characterized by a layer structure, have allowed the synthesis of twelve new alkylammonium compounds. The crystallographic study of these compounds shows that the alkyl chains are oriented in an approximately normal direction to the walls formed by the |TiNbO₅|^? sheets. The particular behaviour of the compound |C₂H₅NH₃|TiNbO₅, which forms a polymer, has been underlined.     

Synthesis of asymmetric biphenyl derivatives for optoelectronic applications

We report the synthesis and optical properties of a series of ten organic compounds with biphenyl as the backbone and asymmetrically modified by triphenylamines, carbazoles and tetraphenylsilanes (BP 1-10). BP 1-10 were synthesized mainly by Ullmann coupling reaction and Suzuki cross-coupling reaction and characterized by EA, NMR, MS, UV–Vis, DSC, TGA, fluorescence spectra and cyclic voltammetry. They exhibit reversible electrochemical behavior with low oxidation potentials and emit intense pure-blue light with high fluorescence quantum yields (up to 80%). BP 1 was fabricated into multi-layered light-emitting diodes as blue-emitting, host and hole transport materials. Based on the performance of BP 1 and the similarity in chemical structure to those compounds reported in literature, these compounds are expected to be good and versatile hole transport, host and blue emitting materials.     

New anthracene-based semi-conducting polymer analogue of poly(phenylene sulfide): Synthesis and photophysical properties

A new anthracene-based polymer analogue of poly(phenylene sulfide) has been synthesized via Wittig polycondensation. The polymer is soluble and shows a good film quality. This organic material showed an amorphous behavior with a T_g of 70 °C. The absorption and fluorescence properties of the polymer were investigated. The HOMO/LUMO energy levels were estimated by cyclic voltammetry measurements. The PAnS thin film exhibits an optical gap of 2.56 eV and emits in orange region. The fluorescence quantum efficiency in dilute solution of PAnS was of 66%. A PAnS-based single-layer diode has been fabricated and shows relatively low turn-on voltage of 4.8 V.     

Spectroscopic characterizations of Er doped LaPO4 submicron phosphors prepared by homogeneous precipitation method

Hexagonal shaped LaPO₄ submicron particles doped with various concentrations of Er were successfully prepared by homogenous precipitation method using metal nitrates and ammonium phosphate. Particles of approximate particle size 125 nm and size distribution of 85 nm are obtained with good crystallinity. After heat treatment at 1200 °C for 2 h, the particles are characterized for their various optical properties such as absorption, emission, fluorescence decay and optical band gap. Optical absorption and emission data are numerically analyzed with the help of Judd–Ofelt model to evaluate various radiative spectral properties such as radiative decay rates, radiative quantum yield, emission cross-section and fluorescence branching ratios of various emission transitions. Though the radiative quantum yield of 1554 nm emission approaches the theoretical limit of 100%, the experimentally measured quantum yield is only 11% at 12 W/cm² at 980 nm excitation power density in 2% Er doped LaPO₄.     

Hydrogen desorption kinetics of MgH2 synthesized from modified waste magnesium

In the present study, hydrogen desorption properties of magnesium hydride (MgH₂) synthesized from modified waste magnesium chips (WMC) were investigated. MgH₂ was synthesized by hydrogenation of modified waste magnesium at 320 °C for 90 min under a pressure of 6 × 10⁶ Pa. The modified waste magnesium was prepared by mixing waste magnesium with tetrahydrofuran (THF) and NaCl additions, applying mechanical milling. Next, it was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques in order to characterize its structural properties. Hydrogen desorption properties were determined by differential scanning calorimetry (DSC) under nitrogen atmosphere at different heating rates (5, 10, and 15 °C/min). Doyle and Kissenger non-isothermal kinetic models were applied to calculate energy (E _a ) values, which were found equal to 254.68 kJ/mol and 255.88 kJ/mol, respectively.