•Two host materials (SPDPPO and SBPBDPPO) were designed and synthesized by using diphenylphosphine oxide as acceptor and spirobifluorene units as donor.•They exhibited excellent thermal properties with the Tg of SPDPPO and SBPBDPPO of 140 and 172 °C.•The green PhOLEDs hosted by SPDPPO using Ir(ppy)3 as dopant displays better performances with ηcmax of 36.5 cd/A.Two novel host materials based on the diphenylphosphine oxide (DPPO) and spirofluorene were designed and facilely synthesized by tuning the ratio of donor spirofluorene units and acceptor DPPO units from 1: 1 to 1: 2, i. e., (4-(9,9′-spirobi[fluoren]-2-yl)phenyl)diphenylphosphine oxide (SPDPPO) and (9,9′-spirobi[fluorene]-2,7-diylbis(4,1-phenylene))bis(diphenylphosphine oxide) (SBPBDPPO). Furthermore, 3,6-disubstituted spirofluorene possesses better thermal stability performance, for instance, higher glass transition temperatures (SPDPPO of 140 °C and SBPBDPPO of 172 °C). The phosphorescent organic light-emitting devices (PhOLEDs) were fabricated by doping tris(2-phenylpyridine)iridium (Ir(ppy)3) in hosts as light-emitting layer. The PhOLEDs employed SPDPPO as host exhibited a low turn-on voltage of 3.0 V and the maximum current efficiency of 36.5 cd/A, power efficiency of 32.8 lm/W and a maximum external quantum efficiency (EQE) of 10.5%, respectively.The two host materials (SPDPPO and SBPBDPPO) were designed and synthesized. The green PhOLEDs using Ir(ppy)3 as phosphorescent dopants were fabricated and hosted by SPDPPO display performances with ηcmax of 36.5 cd/A and low efficiency roll-off.Download high-res image (141KB)Download full-size image

•Small flow hydrogen treatment is conducted at the upper well/barrier interface to improve the quality of active region.•Surface and interface properties are improved when hydrogen treatment is adopted.•Room temperature photoluminescence intensity is significantly enhanced after hydrogen treatment.•The enhancement in optical quality originates from the decreased defect density, rather than carrier localization.To enhance the quality of InGaN/GaN multiple quantum wells (MQWs), a small hydrogen flow is introduced to treat the upper well/barrier interface. High-resolution X-ray diffraction results indicate that hydrogen treatment improves the interface quality of MQWs. Room temperature photoluminescence (PL) tests show that integrated PL intensity is enhanced by 57.6% and line width is narrowed, while emission peak energy is almost unchanged. On the basis of temperature-dependent PL characteristics analysis, it is concluded that hydrogen treatment decreases non-radiative recombination centers in active region, yet has little impact on carrier localization. Moreover, surface roughness and V-pit density are significantly reduced after hydrogen treatment as revealed by atomic force microscopy. Because the emission energy is quite stable after the hydrogen treatment, this method can also be promoted to improve the quality of green and yellow-green emission MQWs.

InGaAs/GaAsP multiple quantum wells (MQWs) were grown by metal–organic chemical vapor deposition on vicinal GaAs (001) substrates with different miscut angles of 0°, 2° and 15° towards [110]. The crystal structures of InGaAs/GaAsP were characterized by high-resolution X-ray diffraction and Raman spectroscopy. The surface morphologies of InGaAs/GaAsP MQWs were observed by atomic force microscopy. The mechanisms for step flow, step bunching and pyramid growth on 0°, 2° and 15° misoriented substrates were discussed. The results provide a comprehensive phenomenological understanding of the self-ordering mechanism of vicinal GaAs substrates, which could be harnessed for designing the quantum optical properties of low-dimensional systems. From low-temperature photoluminescence, it was observed that the luminescence from the MQWs grown on a vicinal surface exhibits a red-shift with respect to the 0° case. An extra emission was observed from the 2° and 15° off samples, indicating the characteristics of quantum wire and pyramidal self-controlled quantum-dot systems, respectively. Its absence from the PL spectrum on 0° surfaces indicates that indium segregation is modified on the surfaces. The relationship between InGaAs/GaAsP MQWs grown on vicinal substrates and their optical and structural properties was explained, which provides a technological basis for obtaining different self-controlled nanostructures.

The growth and strain-compensation behaviour of InGaAs/GaAsP multi-quantum wells, which were fabricated by metal–organic chemical vapor deposition, have been studied towards the application of these quantum wells in high-power laser diodes. The effect of the height of the potential barrier on the confined level of carrier transport was studied by incorporating different levels of phosphorus content into the GaAsP barrier. The crystal quality and interface roughness of the InGaAs/GaAsP multi-quantum wells with different phosphorus contents were evaluated by high resolution X-ray diffraction and in situ optical surface reflectivity measurements during the growth. The surface morphology and roughness were characterized by atomic force microscopy, which indicates the variation law of surface roughness, terrace width and uniformity with increasing phosphorus content, owing to strain accumulation. Moreover, the defect generation and structural disorder of the multi-quantum wells were investigated by Raman spectroscopy. The optical properties of the multi-quantum wells were characterized by photoluminescence, which shows that the spectral intensity increases as the phosphorus content increases. The results suggest that more electrons are well bound in InGaAs because of the high potential barrier. Finally, the mechanism of the effect of the height of the potential barrier on laser performance was proposed on the basis of simulation calculations and experimental results.

•Triple-color hyperbranched white-light polymers were designed and synthesized.•Phosphorescent Ir(piq)3 acts as red core inserted to fluorescent main chains.•The synthesized polymers have good thermostability and film forming ability.•The diodes exhibit excellent electroluminescent performance.A series of triple-color hyperbranched polymers based on poly(9,9-dioctylfluorene) (PF) were designed and synthesized, in which phosphorescent tris(1-phenylisoquinoline)iridium(Ш) (Ir(piq)3) acts as red core and poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,7-diyl)] (PFBT) is inserted as green-emission segment. The synthesized polymers have good thermostability, film forming ability and high fluorescence quantum yield. By tuning the contents of red core and green-emission segment, the optimized triple-color hyperbranched polymer is acquired, named PF-BT250-Ir(piq)325. Furthermore, the PF-BT250-Ir(piq)325 is utilized as single emission layer in white polymer light emitting diode with the configuration of ITO/PEDOT:PSS (50 nm)/PF-BT250-Ir(piq)325 (80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (100 nm). The diode exhibits a maximum luminous efficiency of 1.60 cd/A, a maximum luminance of 3267 cd/m2 and the Commission Internationale de l’Eclairage coordinate of (0.32, 0.34) very close to the pure white point of (0.33, 0.33).Triple-color hyperbranched polymers based on poly(9,9-dioctylfluorene) (PF) with phosphorescent tris(1-phenylisoquinoline)iridium(Ш) (Ir(piq)3) as red core and poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(benzo [2,1,3]thiadiazol-4,7-diyl)] (PFBT) as green segments were designed and synthesized.

Three-dimensional (3D) GaN nanostructures with well-aligned nano-cones have been prepared via a laser interference lithography + inductively coupled plasma (ICP) etching method. The effect of radio-frequency (RF) power and KOH solution etching on morphologies and optical properties of the GaN nano-cones has been studied by scanning electron microscopy, energy dispersive spectroscopy, room-temperature and low-temperature photoluminescence (PL) measurements. Our results show that the sidewall obliquity of GaN nano-cones increases from 63° to 80° with the increase of RF power from 60 W to 120 W, while their height and PL intensity peak at the RF power of 80 W. At 10 K, the excitonic interband ΓV9–ΓC7 and ΓV7 (upper band)–ΓC7 transitions were clearly observed for the GaN nano-cones, which were found to be 3.487 eV and 3.493 eV, respectively. After etching with KOH solution the nano-cones' surface was obviously roughened and their PL intensity increased by around 60%, although their internal quantum efficiency determined by low-temperature PL measurement was only increased by 6%. The enhanced PL intensity could be mainly ascribed to the improved light extraction efficiency and/or light absorption efficiency. It is expected that the 3D GaN nanostructures prepared in the work can offer a new growth template candidate for the fabrication of GaN based nanoLEDs.

•A thermally activated delayed fluorescence (TADF) emitter CyFbCz was developed.•The appropriate combination of donor and acceptor gave efficient blue emitting.•The OLED with CyFbCz dopant achieved a maximum luminance of 2526.8 cd/m2.A D–A structured thermally activated delayed fluorescence (TADF) emitter, CyFbCz, was developed. The combination of 4-fluorocyanophenyl acceptor and carbazolyl donor resulted in an appropriate energy gap for efficient blue emitting. The well separated HOMO and LUMO contributed to a small ΔEST (0.09 eV) and effective reverse intersystem crossing from lowest triplet state (T1) to singlet state (S1). The OLED with CyFbCz dopant achieved a maximum luminance of 2526.8 cd/m2, a maximum current efficiency of 6.64 cd/A, and a CIE coordinate of (0.18, 0.13).

•Three RGB colored complexes were excited by the wavelength of 365 nm.•A theoretical calculation of color scheme according to according to the CIE values was reported.•Serial copolymers were synthesized by free radical copolymerization of three complexes and MMA.•The theoretical calculation was of guidance to tuning of the emission color of the copolymers.In this work, a method of tuning the chromaticity of the emission color of the copolymers containing Eu(III), Tb(III), Be(II) ions based on colorimetric principle was proposed. The technological route from coordination to copolymerization was employed to obtain the white light macromolecular phosphor. The three primary color monomers have been synthesized and their Commission Internationale de L’Eclairage (CIE) coordinates are respectively (0.540, 0.314), (0.231, 0.463), and (0.161, 0.054). The molar feed ratios of the three primary color monomers were calculated from the CIE coordinates based on colorimetric principle. Serial copolymers have been synthesized by free radical copolymerization of the three primary color monomers and methyl methacrylate. The quantum efficiency of the copolymers was higher than that of the complex monomers. The complexes were directly boned to the polymer chain, in which the energy transfer was reduced significantly compared to the doped-polymers. The experimental values of copolymers’ CIE coordinates were located in the white light region in good agreement with theoretical values. The results indicate that the chromaticity of the emission color of the copolymers containing Eu(III), Tb(III), Be(II) ions could be tuned by theoretical calculation based on colorimetric principle.

Three host materials based on the carbazole were designed and facilely synthesized, i. e., 9-(6-(9-carbazolyl)hexyl)carbazole (hCP), 9-(4-(2-thiophene-based)phenyl) carbazole (sCP) and 9-(4-(9-carbazolyl)phenyl)carbazole(pCP). The relationships between the structures and photophysical, electrochemical and electrophosphorescent performances were investigated. Their emission peaks are located in UV region and the optical band gap are 3.51, 3.57, and 3.89 eV, respectively. Hence, they can be used as hosts in phosphorescent organic light-emitting devices (PhOLEDs). The PHOLEDs were fabricated by doping tris(2-phenylpyridine)iridium (Ir(ppy)3) in host as light-emitting materials. The maximum current efficiency of the PhOLEDs employed sCP as host was 44.88 cd/A.Three host materials (hCP, sCP, and pCP) by changing the introduction of different connection groups were designed and synthesized. The sCP exhibited bipolar. The green PhOLEDs using Ir(ppy)3 as phosphorescent dopants were fabricated.

InGaAs/GaAsP multiple quantum wells (MQWs) structures were grown by metal–organic chemical vapor deposition and the effect of the growth temperature on the interfacial crystal quality was characterized by high-resolution X-ray diffraction and photoluminescence. The surface roughness of MQWs was measured by atomic force microscopy for evaluating the surface quality. The existence of an indium diffusion zone (InGaAsP) between InGaAs and GaAsP was demonstrated by secondary ion mass spectrometry profiles in the growth direction. The results suggest the different diffusion widths originate from the growth temperature variation. A smoother surface and higher quality interface of MQWs was obtained at 650 °C growth temperature. Furthermore, the phenomena of current self-oscillations were confirmed through current–voltage measurements at room temperature, which can be attributed to the negative differential resistance effect. The influence of the growth temperature on the crystal quality of InGaAs/GaAsP MQWs was used for the optimization of technological parameters.

A series of white light-emitting hyperbranched copolymers (P2–P5) consisting of polyfluorene/4,7-dithienyl-2,1,3-benzothiadiazole (DBT) branches and spiro[3.3]heptane-2,6-dispirofluorene (SDF) conjugated branching point have been synthesized and fully characterized. The effects of the branching degree on the thermal, photoluminescent and electroluminescent properties of the copolymers were investigated. The results suggest that the branching point helps to enhance both the thermal and spectral stabilities of the hyperbranched copolymers, and retain the energy transfer efficiency from fluorene to DBT unit. Efficient hyperbranched copolymer-based single-layer devices are achieved with CIE coordinates located at near (0.33,0.33). Especially, a device based on P4 (10 mol% of SDF) exhibits a doubled efficiency and 5.5-fold increase in luminance compared to the device based on the linear reference.

A series of hyperbranched copolymers with fluorene-alt-carbazole as the branches and three-dimensional-structured spiro[3.3]heptane-2,6-dispirofluorene (SDF) as the core were synthesized by one-pot Suzuki polycondensation. 4,7-Dithienyl-2,1,3-benzothiadiazole (DBT) as the orange-light emitting unit was introduced into the backbones to obtain white-light emission. The thermal, photoluminescent (PL), electrochemical and electroluminescent (EL) properties of the copolymers were investigated. The copolymers show great thermal stabilities by the introduction of a carbazole moiety. Besides, the HOMO energy levels of the copolymers were enhanced and the hole injection was improved because of the hole-transporting ability of the carbazole unit. The hyperbranched structures suppress the interchain interactions efficiently, and help to form amorphous films. The copolymers exhibit efficient EL performance as a result of the hyperbranched structure with the incorporation of the carbazole moiety. A quite low turn-on voltage of 5.3 V, a maximal luminance of 7409.5 cd m−2 and a luminous efficiency of 4.27 cd A−1 were achieved with a CIE coordinate of (0.32, 0.26) for the PFCzSDF10DBT10 (10 mol% of SDF and 0.1 mol% of DBT) device. The hyperbranched framework based on fluorene-alt-carbazole branches and SDF core are attractive candidates for solution-processable white polymer light-emitting device (WPLED) applications.

The role of the nucleation layer thickness on the GaN crystal quality grown by metal organic chemical vapor deposition is explored. The surface morphologies of a low-temperature GaN nucleation layer (NL) investigated by Atomic Force Microscopy shows the nuclei grain size increases with increasing thickness. After annealing, island-like morphologies of the low-temperature GaN NL are obtained. Increasing the NL thickness is beneficial for obtaining larger island size, however, the uniformity of the island size is deteriorated. The high-resolution X-ray diffraction analysis reveals that bulk GaN crystal properties are closely connected with NL thickness, which can be well explained by the dislocation generation and propagation process in the GaN films. All the obtained results indicate that the NL thickness effectively controls the size and density of the islands and thus determines the crystal properties of GaN films.

A series of novel hyperbranched conjugated polymers containing red phosphorescent iridium complexes that produce white-light emission have been designed and synthesized. The iridium complexes, tris[1-phenylisoquinolinato-C2,N]iridium(III) (Ir(piq)3), as red emitters, are covalently connected with the polyfluorene segments as blue emitters. Based on the hyperbranched structure, the conjugated polymers with large steric hindrance can effectively suppress the triplet–triplet annihilation. Simultaneously, the synthesized polymers express relatively better thermostability, photophysical properties, with a higher fluorescence quantum yield (57–77%), and electrochemical properties. By incorporating about 0.1 mol% of Ir(piq)3 into the conjugated polymers, the white-light emission could be achieved. Single-active-layer polymer light emitting devices with the configuration of ITO/PEDOT:PSS/polymer/TPBI/LiF/Al have been fabricated. Among all the devices, PF-Ir(piq)3100 device exhibits a Commission Internationale de l'Eclairage coordinate of (0.30, 0.23), which is close to that of pure white light. This indicates that the hyperbranched polymers exhibiting mixed fluorescence and phosphorescence emission would be promising white-light materials.

A solution-processable yellow-light-emitting heteroleptic phosphorescent Ir(III) complex of (CzhBTZ)2Ir(fpptz) [CzhBTZ: (2-[2-(6-(9-carbazolyl)hexyl)phenyl]benzothiazole) fpptz: (2-(5-(4-fluorophenyl)-2H-1,2,4-triazol)-3-yl)] was synthesized. Its photophysical, thermal and electroluminescence properties were investigated. Phosphorescent organic light-emitting diodes (PhOLEDs) using (CzhBTZ)2Ir(fpptz) doping in (4,4′-bis(N-carbazolyl)-1,1′-biphenyl) as the emitting layer were prepared by spin-coating with a maximum peak at 533 nm, and International Commission on Illumination (CIE) coordinates of (0.42, 0.56).

•A blue-green self-host phosphorescent iridium(III) complex was synthesized.•The molecular structure, and photophysical properties were investigated.•Electroluminescent performance in host-free devices were discussed.•The maximum current efficiency 8.2 cd A−1 and the maximum brightness 5420 cd m−2 were achieved.A kind of blue-green self-host phosphorescent iridium(III) complex, (CzPhBI)2Ir(tfmptz) [CzPhBI = 9-(6-(2-phenyl-1-benzimidazolyl)hexyl)-9-carbazole; tfmptz = 2-(5-trifluoromethyl-1,2,4-triazolyl)pyridine], was designed and synthesized. The synthesized iridium(III) complex was characterized by 1H NMR, 19F NMR, FT-IR, elemental analysis and X-ray single-crystal diffraction, respectively. Its thermal properties, optical properties and electrochemical properties were also investigated. The host-free organic electroluminescent devices with the configuration of ITO/MoO3 (3 nm)/NPB (30 nm)/TAPC (15 nm)/(CzPhBI)2Ir(tfmptz) (30 nm)/TBPI (30 nm)/LiF (1 nm)/Al (100 nm) had been fabricated. The devices exhibited excellent performance indicating that (CzPhBI)2Ir(tfmptz) was a promising phosphorescent material.

A series of hyperbranched fluorescence/phosphorescence hybrid copolymers with 9,9-dioctylfluorene and bis(1-phenyl-isoquinoline)(acetylacetonato)iridium(III) (Ir(piq)2acac) as the branches and the three-dimensional structured spiro[3,3]heptane-2,6-dispirofluorene (SDF, 10 mol %) as the core have been synthesized by adjusting the feeding ratios of Ir(piq)2acac (0.02–0.05 mol %). The copolymers showed good thermal and spectral stability, and amorphous film morphology because of the hyperbranched structures. The 2,7-substituted fluorenes of SDF were incorporated into the π-system of the polyfluorene branches, and remained the Förster resonance energy transfer (FRET) efficiency from fluorene segment to Ir(piq)2acac unit. The copolymers exhibited efficient electroluminescent characters, and white-light emission was achieved in PFSDF-Ir4 (Ir(piq)2acac 0.04 mol %)-based single layer device with CIE coordinates at (0.30, 0.34), a maximum luminance of 6777.3 cd/m2 (at 18.3 V), and a maximum current efficiency of 4.0 cd/A.A potential hyperbranched structure with 9,9-dioctylfluorene and Ir(piq)2acac branches, and three-dimensional-structured spiro[3.3]heptane-2,6-dispirofluorene (SDF) core is synthesized for efficient and stable white polymer light-emitting devices.

Novel one-dimensional SiC@carbon nanotube (CNT) coaxial nanocables have been successfully fabricated on a large scale by using a carbothermal chemical vapor deposition method. Sol–gel-derived silica xerogels containing commercial multi-wall carbon nanotubes (MWCNT) were used as silicon and carbon sources. The obtained product was characterized by SEM, HRTEM, Raman spectroscopy and XRD. The coaxial nanocables have been found to be composed of a 40–100 nm diameter carbon nanotube as the core, surrounded by a thick SiC outlayer. The inner nanotube corresponded to the multi-walls of the carbon nanotube with a lattice spacing of 0.34 nm. The PL spectrum revealed that the SiC@CNT nanocables have two broad emission bands centered at 461 nm and 573 nm which can be attributed to the quantum confinement effect and the morphology effects. The morphology of the product was tuned by simply altering the reaction temperature. In the formation of SiC@carbon nanotube coaxial nanocables, it was proposed that CNTs acted as a template to confine the reaction, which resulted in the continuous SiC outlayer growth on the CNT surface to form SiC@CNT coaxial nanocables.

•SiC networks were grown on silicon substrate by the direct synthetic method.•Network was constructed by SiC nanowire junctions.•The growth processes rely on the VLS model, branched growth and SiO2 deposition.•The PL spectrum indicated SiC networks have ultraviolet and blue emission properties.Nanoscale SiC networks were prepared by using carbothermal reaction between silica xerogels and carbon nanoparticles in an argon atmosphere on the silicon substrate. Microstructure characterizations indicate that the SiC networks were composed of single-crystalline SiC interconnected nanowires wrapped with amorphous SiO2 layer. The diameter of interconnected nanowires was 50–400 nm. SiC nanowires were grown by vapor–liquid–solid (VLS) mechanism using Ni as catalyst. The construction of networks mainly depended on SiC nanowire branched growth processes and the welding processes by SiO2 deposition on adjacent nanowires to form junctions. Such nanowire networks are important to meet the requirements of electronics and optoelectronics device integration.

•White light emission achieved using the monomer and excimer emission from single Pt-4 dopant.•Extremely low efficiency roll-off even at luminance exceeding 6000 cd/m2.•Device efficiency has been improved by at least two times with further doping of Ir(ppy)3.•By utilization of TPBi as space layer, the device performance was further improved.Phosphorescent white organic light-emitting diodes (WOLEDs) based on single doped platinum(II) [1,3-difluoro-4,6-di(2-pyridinyl)benzene] chloride (Pt-4) emission layers were investigated in this paper. The devices exhibited electroluminescence spectra composed of bluish (λmax = 480 nm) and reddish (λmax = 660 nm) emission bands, which corresponding to monomer and excimer emission originated from Pt-4 dopants. With optimized device structures, a maximum current efficiency of 11.5 cd/A was obtained and remained above 10 cd/A even the brightness was over 6000 cd/m2. Furthermore, by integrating the fac-tris(2-phenylpyridine) iridium(III) as a complementary emitter and an additional 2,2′,2″-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole) space layer, the device efficiency was further improved, which exhibited a maximum current efficiency of 20.4 cd/A at the luminance of 100 cd/m2, and maintained the mild efficiency roll-off that similar to its single Pt-4 doped counterpart.

Submicrometer-scale ZnO composite aggregate arrays of nanorods and nanoparticles were prepared by simple wet-chemical route and studied as dye-sensitized solar cells (DSSCs) photoanodes. The ZnO composite aggregate arrays significantly improved the efficiency of DSSCs due to their relatively high surface area, fast electron transport, and enhanced light-scattering capability. A short current density (Jsc) of 11.7 mA/cm2 and an overall solar-to-electric energy conversion efficiency (η) of 3.17% were achieved for the ZnO composite aggregate DSSCs, which were much higher than those obtained for the monodisperse aggregate DSSCs (Jsc = 6.9 mA/cm2, η = 1.51%) and ZnO nanorod array DSSCs (Jsc = 4.2 mA/cm2, η = 0.61%).

Ab initio density functional theory (DFT) was employed to study geometric and electronic structure of MgF2 (110) surface. Three different clean surface models have been considered. The results show that the surface terminated with one-layer F has the smallest relaxation and the lowest surface energy, which indicates this model is the most energetically favorable structure of MgF2 (110) surface. Furthermore, the electronic properties are also discussed from the point of density of states and charge density. Analysis of electronic structure shows that the band gap of the surface is significantly narrowed with respect to the bulk. The electrons of the surface exhibit strong locality and larger effective mass.

The reaction mechanism of ceria as an anode in a lithium ion battery (LIB) is unknown. To solve this issue, a nano-LIB was constructed inside a transmission electron microscope (TEM) using an individual CeO2/graphene composite as the anode. The lithiation/delithiation cycles of the CeO2/graphene composite were conducted inside the TEM, and the electrochemical process was in situ monitored by simultaneous determination of the microstructure with high-resolution TEM, electron diffraction, and electron energy loss spectroscopy. The surfaces of the graphene nanosheets and ceria nanoparticles were covered by a nanocrystalline Li2O layer after lithiation, and the Li2O layer shrank and showed partially reversible changes after delithiation. The CeO2 nanoparticles showed imperceptible volumetric and morphological changes, while comprehensive analysis revealed a fully reversible phase transformation between fluorite CeO2 and cubic Ce2O3 during the electrochemical process. These results give direct evidence and profound insights into the lithiation/delithiation mechanism of CeO2/graphene anode in a LIB.

Eu3+ and Sm3+ activated M2SiO4 (M=Ba, Sr and Ca) red-emitting phosphors were synthesized by a solid state reaction. The results of XRD and SEM measurements show that the samples are single phase and have irregular shape. The excitation and emission spectra indicate that these phosphors were effectively excited by ultraviolet (395 nm) and blue (466 nm) light and exhibited red performance. The charge compensator R+ (R+=Li+, Na+ and K+) injecting into the host efficiently enhanced the luminescence intensity of the M2SiO4: Eu3+ and M2SiO4: Sm3+ phosphors. The emission intensity of M2SiO4: Eu3+ and Sm3+ doping Li+ were higher than that of Na+ or K+.Highlights► Eu3+ and Sm3+ doped M2SiO4 (M=Ba, Sr and Ca) red phosphors synthesized by a conventional solid state reaction. ► Ba2SiO4: Eu3+ phosphor has the strongest emission intensity and the best CIE chromaticity in the M2SiO4: Eu3+ phosphors. ► The emission intensity of Ca2SiO4: Sm3+ was the strongest in the M2SiO4: Sm3+ phosphors. ► The introduction of Li+, Na+ and K+ ions as charge compensator led to increased luminescent intensity. ► Li+ showed better efficient luminescent enhancement than Na+ and K+.

Using a combination of scanning electron microscopy and X-ray diffraction techniques, the mechanism for ZnO formation was studied by simply heating an aqueous solution containing zinc salts and ammonium hydroxide to 85 °C. Growth of ZnO occurred via the initial precipitation of stable ε-Zn(OH)2 microcrystals and subsequent formation of ZnO under these conditions. By monitoring an intermediate growth stage, phase transformation from ε-Zn(OH)2 to ZnO was found to take place either via a dissolution–reprecipitation mechanism or via an in situ crystallization transformation mechanism that involves dehydration and internal atomic rearrangements. These findings may contribute to control the synthesis of ZnO in liquid media.Highlights► The mechanism for ZnO formation by heating an aqueous solution was studied. ► ZnO occurred by the initial precipitation of stable ε-Zn(OH)2 microcrystals ► In situ crystallization transformation mechanism was found.

A series of polymers were synthesized by incorporating low contents of fluorenone (FO) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (DBT) into the main chain of poly(9,9-dioctylfluorene). White-light emission was obtained from a single polymer by adjusting the FO and DBT contents. All polymers showed good thermal stability with 5% weight loss up to 410 °C and good solubility in common organic solvents. Electroluminescence devices with indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/emission layer/Ca/Al structure were found to emit white light with Commission Internationale de l’Eclairage coordinate of (0.37, 0.34). These devices exhibited a maxium brightness of 3414 cd/m2 and a maximum current efficiency of 2.79 cd/A.

Sr2SiO4:Eu3+ and Sr2SiO4:Eu3+ doped with R+(R+=Li+, Na+ and K+) phosphors were prepared by conventional solid-state reaction and investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy. XRD patterns and SEM reveal that the optimal firing condition for Sr2SiO4:Eu3+ was 1300 °C for 4 h. The excitation and emission spectra indicate that the phosphor can be effectively excited by ultraviolet (395 nm) and blue (466 nm) light and emits intense red light peaked at around 614 nm corresponding to the 5D0→7F2 transitions of Eu3+. In the research work, the effect of R+ contents on luminescence property and the Eu3+ concentration quenching process have also been investigated. The Eu3+ concentration quenching mechanism was verified to be a multipole–multipole interaction and the critical energy-transfer distance was calculated to be around 14.6 Å. The dopant R+(R+=Li+, Na+ and K+) as charge compensator in Sr2SiO4:Eu3+ can further enhance luminescence intensity, and the emission intensity of Sr2SiO4:Eu3+ doping Li+ is higher than that of Na+ or K+.Highlights► R+ doped Sr2SiO4:Eu3+ phosphors synthesized at different calcinations temperatures. ► Discussed influence of Eu3+ and R+(R=Li+, Na+ and K+) concentration. ► Optimal concentration of Eu3+ is 6 mol%. ► Co-doped charge compensation R+ lead to the increase of emission intensity. ► Li+ optimal concentration was 6 mol% as a better charge compensator than Na+ and K+.

Ammonium polyphosphate (APP)/polypropylene (PP) composites were prepared by melt blending and extrusion in a twin-screw extruder. APP was first modified by a silane coupling agent KH-550 then added to polypropylene. The surface modification of APP by the coupling agent decreased its water solubility and its interface compatibility with the PP matrix. Limiting oxygen index (LOI) and thermogravimetric analysis (TGA) were used to characterize the flame retardant property and the thermal stability of the composites. The addition of APP improved the flame retardancy of PP remarkably. The crystal structures of APP/PP composites were characterized by X-ray diffraction (XRD). The results indicated that β-crystal phase PP may be formed. The structures and morphologies of APP, KH-550/APP and APP/PP composites were characterized by field-emission scanning electron microscope (FESEM). The mechanical property tests showed good mechanical properties of composite materials. Compared with unmodified one, the impact strength, tensile strength and elongation of modified APP/PP were all improved.

An efficient white-light emitting diode ITO/NPB/Zn(4-TfmBTZ)2/Alq3/LiF/Al was obtained when a new material bis(2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazolate)zinc [Zn(4-TfmBTZ)2] was used as an electron-acceptor emitting layer, NPB as an electron-donor emitting and hole-transporting layer, and Alq3 as an emitting and electron-transporting layer. In this device, the exciton emissions of NPB, Zn(4-TfmBTZ)2 and Alq3 in addition to the electroplex emissions of Zn(4-TfmBTZ)2/NPB interface render white light output. Inserting an Alq3 layer with appropriate thickness can increase EL efficiency and improve chromaticity. The most pure white light emission with CIE coordinates of (0.30, 0.34) and CRI of 90.2 can be attained by adjusting Alq3 layer thickness to 20 nm. Moreover, CIE coordinates are very insensitive to the applied voltage. The CIE coordinate region is (0.29–0.30, 0.33–0.34) at various forward bias (8–13 V). This device showed the maximum luminance of 2445 cd/m2 at 14 V and the maximum current efficiency of 1.39 cd/A, which will be improved further by optimizing the preparation technique of device.Graphical abstractResearch highlights► The electroplexes form at NPB/Zn(4-TfmBTZ)2 interface. ► The combining emission of excitons and electroplexes render white light output. ► EL efficiency and chromaticity of device are dramatically controlled by thickness of Alq3 layer. ► The idea white light emission can be attained by adjusting Alq3 thickness to 20 nm.

In this article, the molecular structure, photoluminescent and electroluminescent properties of bis(2-(4-methyl-2-hydroxyphenyl) benzothiazolate) zinc (Zn(4-MeBTZ)2) with good electron-transport characteristics were reported. This complex was identified as triclinic structure with the strong intermolecular π–π stacking interactions between the benzothiazolate/phenoxido rings and weak intramolecular hydrogen bonds by X-ray single-crystal diffraction. Quantum chemical method has been employed to investigate electron structure and charge transport property. The blue-green light emission was observed by fabricating double-layer devices using Zn(4-MeBTZ)2 as electron-transport and NPB as hole-transport material. The performance of organic light-emitting devices based on Zn(4-MeBTZ)2 is much better than that of the devices based on [Zn(BTZ)2]2.Graphical abstractHighlights► The synthesis, crystal structure and photophysical properties of Zn(4-MeBTZ)2 were reported. ► The electron-transport property was investigated by theoretical calculations and experimental. ► We found that Zn(4-MeBTZ)2 has a higher electron mobility than that of [Zn(BTZ)2]2 and the devices based on it have a lower turn-on voltage.

An eco-friendly method was put forward to synthesize Ag nanoparticles (Ag NPs) by using biodegradable starch as a stabilizing agent. The silver ion from AgNO3 was reduced by glucose in soluble starch solution. Morphological observation and characterization of Ag NPs were performed by using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and UV–vis absorption spectroscopy. HRTEM showed that Ag NPs were covered by starch layer to form spherical core-shell Ag/starch NPs with diameter ranging from 5 to 20 nm. XRD pattern confirmed the presence of Ag NPs with face-centered cubic (fcc) structure. All these results indicated that starch played an important role in stabilizing Ag NPs.

A series of methyl-substituted bis(2-(hydroxyphenyl)benzothiazolate)zinc derivatives [Zn(n-MeBTZ)2, n = 3 (1a), 4 (1b), 5 (1c)] were synthesized to investigate the correlation between molecular structures and optical properties. The results indicate that the blue-emitting (λmax = 470 nm) complex 1b is monomer with a higher PL quantum efficiency than complexes 1, 1a, 1c. Two green-emitting (λmax = 507 nm and 499 nm) complexes 1a and 1c have special bi-molecular structures. The molecular structure for Zn(BTZ)2 (complex 1) is dimer. Bilayer organic light-emitting devices were fabricated by using these complexes as emitting layer. The maximum emission wavelengths of the devices are in the range of 501–553 nm. The devices show turn-on voltages at 9.2, 12.7, 2.3 and 10.7 V for complex 1, 1a, 1b, and 1c, respectively. In particular, the device with complex 1b shows a higher brightness than the other complexes under the same conditions.

To search for a high sensitivity sensor for cysteine, we investigated the adsorption of cysteine on intrinsic and Au-doped graphene sheets using density functional theory calculations. Binding energy is primarily determined by the type of atom which is closer to the adsorbed sheet. Compared with intrinsic graphene, Au-doped graphene system has higher binding energy value and shorter connecting distance, in which strong Au-S, Au-N and Au-O chemical bond interaction play the key role for stability. Furthermore, the density of states results show orbital hybridization between cysteine and Au-doped graphene sheet, but slight hybridization between the cysteine molecule and intrinsic graphene sheet. Large charge transfers exist in Au-doped graphene-cysteine system. The results of DOS and charge transfer calculations suppose that the electronic properties of graphene can be tuned by the adsorption site of cysteine. Therefore, graphene and Au-doped graphene system both possess sensing ability, except that Au-doped graphene is a better sensor for cysteine than intrinsic graphene.

In this study, a series of Y3Al5O12:Ce3+, Gd3+ nano-phosphors were prepared using a simply wet chemical process with polyvinyl pyrrolidone as a modifier. The crystal and bonding structures of Y3Al5O12:Ce3+, Gd3+ nano-phosphors prepared with different weight percentages of polyvinyl pyrrolidone were characterized by X-ray diffractometry and infrared spectrometry. The decomposition process of dried precursor gel with adding 1.37 wt% polyvinyl pyrrolidone was investigated by differential thermal and thermogravimetric analysis. The effect of surface modification on photoluminescence properties for the samples was studied. The results show that the steric hindrance effect of polyvinyl pyrrolidone leads to high dispersion and good crystallinity of Y3Al5O12:Ce3+, Gd3+ nano-phosphors prepared with adding a proper weight percentages of polyvinyl pyrrolidone. Adding polyvinyl pyrrolidone is beneficial for the photoluminescence enhancement of the samples, which is attributed to the promotion of the incorporation of Ce3+ and Gd3+ into the Y3Al5O12 nanocrystal and the surface passivation of the nano-particles by the polyvinyl pyrrolidone molecules.

Crystals of semiconductor ZnO were fabricated by means of solid-vapor growth method—carbon thermal reduction. Powder X-ray diffraction and field emission scanning electron microscope were used to characterize the phase and morphology of the samples. The results showed that the samples were wurtzite ZnO crystals and anisotropy of crystal growth relied on reaction temperature in solid-vapor process. The crystals synthesized at different temperatures were of short column-like shape, flat top hexagon pyramidal-like shape and polyhedron shape. The growth mechanisms of the above three kinds of crystal were consistent with the theory of growth basic structural unit of negative ion coordination polyhedron. At first, Zn2+ and four O2− form [Zn-O4]6− coordination tetrahedron at any temperature. Then, tetrahedrons stack in different ways into different morphology crystal at different temperatures.

Novel flower-like vanadium carbide (V8C7) hierarchical nanocrystals have been successfully synthesized in a large-scale hydrothermal process using a mixture of diethanolamine (HN(C2H4OH)2, DEA) and V2O5 powder. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), selected-area electron diffraction (SAED) and energy-dispersive spectra (EDS). The results showed that flower-like products consist of very thin sheets with an average thickness of 10 nm and the nanosheets were a uniform single-crystalline V8C7 phase. It was found that reaction temperature and type of capping molecules have a crucial influence on the morphology of the products. A possible growth mechanism of the flower-like V8C7 hierarchical nanocrystals is proposed and discussed.

Sr2CeO4, pure and doped with Eu3+ ions of different concentrations, were synthesized by polyacrylamide gel method. First principles were applied to calculate the electronic structures and band gap of Sr2CeO4. The results show that a broad emission band originating from Sr2CeO4 host and Eu3+ emission lines in blue, green, and red regions coexist. The increase in Eu3+ concentration results in the luminescence intensity redistribution between the Sr2CeO4 host and the doping ion. The energy transfer model clarifies the possible mechanisms of energy transfer from Sr2CeO4 host to Eu3+ in Sr2CeO4:Eu3+ phosphor.Research highlights▶ The theoretical result of Eg, which is 2.64  eV, agrees well with the experiment. ▶ The valence and conduction bands are mainly of O 2p and Ce 4f orbital, respectively. ▶ The energy transfer is from Sr2CeO4 host to Eu3+ in Sr2CeO4:Eu3+ phosphor.

Hydrophobic magnesium hydroxide nanoparticles were obtained by means of grafting poly(methyl methacrylate) (PMMA) onto the surface of nanoparticles after oleic acid (OA) modification. The introduction of functional double bonds was firstly conducted on the surface of nanoparticles by OA modification, followed by dispersion polymerization on the particles surface in ethanol solution using methyl methacrylate (MMA) as monomer, azoisobutyronitrile (AIBN) as initiator and polyvinylpyrrolidone (PVP) as stabilizer to graft PMMA on the surface of OA-modified magnesium hydroxide. The obtained composite particles were characterized by XRD, FTIR, TGA, FESEM–EDS, and the compatibility with organic solution was determined by sedimentation test. The results show that the organic macromolecule PMMA could be successfully grafted on the surface of OA-modified magnesium hydroxide nanoparticles, with the dispersibility and the compatibility of nanoparticles greatly improved in organic phase.A facile surface modification was used to obtain hydrophobic magnesium hydroxide nanoparticles via PMMA grafting by dispersion polymerization after oleic acid modification. Surface modified nanoparticles could float over water for 30 days and homogeneously disperse in the liquid paraffin with no noticeable sedimentation for 2 weeks.

As the size of the fullerene cage increases, the possibility for the existence of multiple isomers also increases. Most fullerenes and endohedral fullerenes obey the isolated pentagon rule (IPR), which requires that each of the twelve pentagons in the carbon cage be surrounded by hexagons. Non-IPR structures have already been isolated for cages containing 66, 68, 70, 72, 74, 78 or 84 carbon atoms. The structural characteristics of the endohedral metallofullerenes, which consist of carbon cages from C66 to C84 and encaged species including one, two, three atoms, metal nitrides(M3N) or metal carbides(M2C2) are illustrated.

Copolymers of 9,9-dioctylfluorene (DOF) and 2-thienyl-benzothiadiazole (DBT) were synthesized by Suzuki reaction and end-capped by N-hexyl-carbazole and benzene, which were abbreviated as PDOF-DBT-Cz and PDOF-DBT-B, respectively. The photophysical, electrochemical and thermal properties of the copolymers were studied. The results indicated that replacement of N-hexyl-carbazole as end-capping group of PDOF-DBT can vary light color and improve luminescence efficiency.

Excellent ignition-proof performance is realized in the system of Mg-Y-Ca, which can be melted at 1173 K directly in air without any protections. When the concentration of Y is greater than 10 wt pct, a dense and compact oxide film is obtained on the surface of molten Mg-Y alloy. With the addition of Ca, the critical concentration of Y in Mg-Y alloys for forming the protective film is decreased significantly from 10 to 3.5 wt pct. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Auger electron spectroscopy (AES) analyses indicate that the protective film formed on the surface of Mg-Y-Ca alloy melt is mainly composed of Y2O3. Based on the theoretic analysis and experimental results, a selective oxidation model of Mg-Y alloys at high temperatures is developed, and the third-element effects of Ca are discussed in detail.

Well-dispersed magnesium hydroxide nanoplatelets were synthesized by a simple water-in-oil (w/o) microemulsion process, blowing gaseous ammonia (NH3) into microemulsion zones solubilized by magnesium chloride solution (MgCl2). Typical quaternary microemulsions of Triton X-100/cyclohexane/n  -hexanol/water were used as space-confining microreactors for the nucleation, growth, and crystallization of magnesium hydroxide nanoparticles. The obtained magnesium hydroxide was characterized by field-emission scanning electron microscopy (FESEM), high-resolution transmission election microscopy (HRTEM), X-ray powder diffraction (XRD), laser light scattering, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis–differential scanning calorimetry (TGA–DSC). The mole ratio of water to surfactant (ω0)(ω0) played an important role in the sizes of micelles and nanoparticles, increasing with the increase of ω0ω0. The compatibility and dispersibility of nanoparticles obtained from reverse micelles were improved in the organic phase.This paper focuses on the synthesis of well-dispersed and size-controllable magnesium hydroxide nanoparticles with uniform shape and even size in a quaternary microemulsion of Triton X-100/cyclohexane/n-hexanol/water.

The electronic parameters of fullerenes are essential for their potentials used as active layers in organic solar cells. Two isomeric forms of the C60 ([5,6] fulleroid and [6,6] methanofullerene), named [60] PCBM (phenyl-C61-butyric acid methyl ester) clusters, were calculated using the B3LYP method with the 6-31G(d) basis set. It has been found that the contraction of C6−6 double bonds is favorable for addition. The first adiabatic electron affinity (AEA) for [60] PCBM is similar to that for C60. The energy gaps between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO) of [60] PCBM have been reduced compared with C60. PCBM derivatives show an increased level of LUMO of fullerenes. From the natural charge populations, it has been found that adding a PCBM unit onto the C60 cages does not change the charge populations remarkably; attaching a PCBM has no effect on the electronic structures of C60. The results of theoretical calculation suppose that PCBM is not involved in the process of photoelectric conversion, but it plays a key role in adjusting the level of HOMO−LUMO for increasing photoelectric conversion efficiencies.

•Nucleation layer thickness can effectively control the nucleation sites.•Nucleation sites formed mainly in the trenches are good for GaN crystal quality.•Longer nucleation time is good at nucleation in the trenches.•Nucleation islands on the sidewalls can not coalesce to a continuous film easily.The role of nucleation layer thickness on the GaN crystal quality grown on cone-patterned sapphire substrate (PSS) was explored. The morphologies of epitaxial GaN at different growth stages were investigated by a series of growth interruption in detail. After 10- and 15-min three-dimensional growth, the nucleation sites are very important for the bulk GaN crystal quality. They have a close relationship with the nucleation layer thickness, as confirmed through the scanning electron microscope (SEM) analysis. Nucleation sites formed mainly on patterns are bad for bulk GaN crystal quality and nucleation sites formed mainly in the trenches of PSS mounds are good for bulk GaN crystal quality, as proved by X-ray diffraction analysis. Nucleation layer thickness can effectively control the nucleation sites and thus determine the crystal quality of bulk GaN.

The growth and strain-compensation behaviour of InGaAs/GaAsP multi-quantum wells, which were fabricated by metal–organic chemical vapor deposition, have been studied towards the application of these quantum wells in high-power laser diodes. The effect of the height of the potential barrier on the confined level of carrier transport was studied by incorporating different levels of phosphorus content into the GaAsP barrier. The crystal quality and interface roughness of the InGaAs/GaAsP multi-quantum wells with different phosphorus contents were evaluated by high resolution X-ray diffraction and in situ optical surface reflectivity measurements during the growth. The surface morphology and roughness were characterized by atomic force microscopy, which indicates the variation law of surface roughness, terrace width and uniformity with increasing phosphorus content, owing to strain accumulation. Moreover, the defect generation and structural disorder of the multi-quantum wells were investigated by Raman spectroscopy. The optical properties of the multi-quantum wells were characterized by photoluminescence, which shows that the spectral intensity increases as the phosphorus content increases. The results suggest that more electrons are well bound in InGaAs because of the high potential barrier. Finally, the mechanism of the effect of the height of the potential barrier on laser performance was proposed on the basis of simulation calculations and experimental results.