Eu3+ ions activated NaLaMgWO6 phosphors were successfully synthesized by an improved sol-gel method using citric acid and polyethylene glycol as complexing agents. Crystal structure and doping site ...were investigated by XRD, Rietveld refinement and Raman spectra. The phosphors had monoclinic double perovskite structure with space group C2/m, as well as layered ordering of A-site and rock-salt ordering of B-site. The blueshift of Raman T2g(1) mode manifested Eu3+ ions had entered into A-site. Thereafter, luminescence properties, such as excitation and emission spectra, CIE coordinates, concentration quenching and thermal quenching were discussed. The quenching concentration for hypersensitive electric dipole transition of Eu3+ reached up to 50.0mol%. The delayed concentration quenching was observed in NaLaMgWO6: Eu3+ phosphor. The theoretical quenching concentration was obtained based on L. Ozawa's theory, and the quenching mechanism on Dexter's theory. Excellent thermal stability of this phosphor shows that it is a potential red phosphor for solid state lighting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We report an inverted and multilayer quantum dot light emitting diode (QLED) which boosts high efficiency by tuning the energy band alignment between charge transport and light emitting layers. The ...electron transport layer (ETL) was ZnO nanoparticles (NPs) with an optimized doping concentration of cesium azide (CsN
) to effectively reduce electron flow and balance charge injection. This is by virtue of a 0.27 eV upshift of the ETL's conduction band edge, which inhibits the quenching of excitons and preserves the superior emissive properties of the quantum dots due to the insulating characteristics of CsN
. The demonstrated QLED exhibits a peak current efficiency, power efficiency and external quantum efficiency of up to 13.5 cd A
, 10.6 lm W
and 13.4% for the red QLED, and correspondingly 43.1 cd A
, 33.6 lm W
and 9.1% for green, and 4.1 cd A
, 2.0 lm W
and 6.6% for the blue counterparts. Compared with QLEDs without optimization, the performance of these modified devices shows drastic improvement by 95.6%, 39.4% and 36.7%, respectively. This novel device architecture with heterogeneous energy levels reported here offers a new design strategy for next-generation high efficiency QLED displays and solid-state lighting technologies.
High sinterability nano-Y
2
O
3
powders for transparent ceramics were successfully synthesized via the decomposition of hydroxyl-carbonate precursors from spray coprecipitation. The chemical ...composition of the precursor was determined as Y(CO
3
)(OH)·
n
H
2
O (
n
= 1–1.5), and it was evolved into Y
2
O
3
particles with clear facets after calcination with the assistance of sulfate. Two dispersion mechanisms, “absorption” and “intercalation,” were proposed to work together to provide the dispersion effect. Microstructural and optical characterization of powders and as-fabricated transparent ceramics was employed to evaluate the sintering behavior of powders. The nanopowders calcined at 1250 °C had weakly agglomerated morphology with the mean particle size of ~140 nm and exhibited excellent sinterability. The in-line transmittance of Y
2
O
3
ceramic of 1 mm thickness that was vacuum sintered at 1800 °C for 8 h without any sintering additives reached 78.7% at 1064 nm.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Herein, a highly-efficient quantum dot light-emitting diode (QLED) with stacked blue and yellow quantum dot (QD) layers can be demonstrated to output white light. A buffer layer of ZnO nanoparticles ...(NPs) inserted between two QD layers can prevent them from mixing and penetrating. In order to promote charge balance, Zn 0.95 Mg 0.05 O was employed as the electron transport layer (ETL), which can block excessive electrons due to the 0.07 eV higher conduction band minimum (CBM) level compared to that of pristine ZnO, leading to the suppression of exciton quenching. In addition, the lower defect concentration and lowered conductivity of Zn 0.95 Mg 0.05 O due to the reduction of oxygen vacancies by doping the Mg element into ZnO can also benefit the inhibition of exciton quenching. The device can be demonstrated with a maximum luminance current efficiency of 24.6 cd A −1 and power efficiency of 25.8 lm W −1 , exhibiting a 19% and 38% enhancement, respectively. The strategy demonstrated here demonstrates a promising way to realize highly efficient white QLEDs and also other optoelectronic devices.
An enormous challenge exists in the development of low-density and efficient microwave absorbers with thin matching thickness. Carbon materials with hierarchical porosity are regarded as potential ...candidates for practical applications of microwave absorption (MA) materials on account of their rich pore structure which facilitates the entry and attenuation of electromagnetic waves. Herein, ordered mesoporous carbon with hierarchical interconnected network structure (NOMC) was prepared through a self-assembly method and calcination treatment. It was found that by adjusting the annealing temperature, the hierarchical porous structure, the carbon defect, the dielectric loss property and the MA property could be tuned. Thanks to the balance between sufficient hierarchical porous structure, outstanding impedance matching condition and multiple loss modes, NOMC displays outstanding ability to dissipate electromagnetic waves at a very thin absorbing coating thickness. Notably, as-prepared NOMC-700 displays an outstanding MA property, whose minimum reflection loss (RLmin) value reaches −27.5 dB at 16.72 GHz and the effective absorption bandwidth (EAB) achieves 3.2 GHz (14.8–18 GHz) under 1.5 mm absorbing coatings. Hence, the satisfying design in porous microstructure can pave the way for efficient MA materials with thin matching thickness.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Transparent YAG ceramics were fabricated by solid state reaction sintering using divalent dopants (CaO and MgO) as sintering additives without TEOS doping, and the effects of divalent dopants on ...their microstructure evolution and optical properties were investigated. It was found that CaO was more effective with respect to inhibiting grain growth than MgO, but not as effective as MgO in promoting densification. Fully dense, transparent YAG ceramics with excellent optical qualities could be achieved by optimizing the doping concentrations of CaO and MgO; the transmittance at 1064nm was as high as 84.5% for 3mm thick sample at the molar ratio of Ca: Mg=1:4, after sintered at 1840°C for 8h in vacuum.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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► Barium hexagonal ferrite was synthesized by adsorbent-combustion method. ► The whole preparation procedure was accomplished within 8h. ► The particles exhibited homogeneous ...hexagonal-plate shape with high aspect ratio. ► The absorber showed excellent microwave absorbing properties.
Barium hexagonal ferrite BaZn2Fe16O27 was rapidly synthesized by adsorbent combustion method. The whole preparation time was controlled within 8h. The microstructures were studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FT–IR). The results showed that the pure BaZn2Fe16O27 was obtained after calcined at 1200°C and the particles exhibited homogeneous hexagonal-plate shape with high aspect ratio. Moreover, the complex permeability (μr=μ′-jμ″) and the complex permittivity (εr=ε′-jε″) were measured in the frequency range of 8–12GHz (X-band) and 12–18GHz (Ku-band) using the network analyzer. The as-prepared ferrite exhibited strong magnetic loss properties. The microwave absorbing properties of the single BaZn2Fe16O27 ferrite layer with different thicknesses were also analyzed. The results showed that the minimum reflection loss was −15.3dB and the bandwidth of reflection loss less than −10dB reached 7.7GHz with the absorber thickness only 1.7mm. The adsorbent combustion method is a kind of ideal method to rapidly prepare barium hexagonal ferrite with excellent microwave absorbing properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► It is well known that the use of TEOS as sintering aid is required to reach fully dense and transparent Nd:YAG ceramics. However, it is difficult to produce high quality transparent Nd:YAG ceramics ...only using TEOS as sintering aid. In this present work, high quality transparent Nd:YAG ceramic was fabricated using both TEOS and MgO as sintering aids. There have been few reports that both TEOS and MgO were co-added as sintering aids in YAG or Nd:YAG transparent ceramics to date. The transmittance of Nd:YAG ceramic is 83.8% at 1064
nm. The effect of MgO on the optical properties of transparent ceramics was also studied.
Neodymium doped YAG transparent ceramics were fabricated by vacuum reactive sintering method using commercial α-Al
2O
3, Y
2O
3 and Nd
2O
3 powders as the starting materials with both tetraethyl orthosilicate (TEOS) and MgO as sintering aids. The morphologies and microstructure of the powders and Nd:YAG transparent ceramics were investigated. Fully dense Nd:YAG ceramics with average grain size of ∼10
μm were obtained by vacuum sintering at 1780
°C for 8
h. No pores and grain-boundary phases were observed. The in-line transmittance of the ceramic was 83.8% at 1064
nm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Upconversion devices (UCDs) have motivated tremendous research interest with their excellent potential and promising application in photovoltaic sensors, semiconductor wafer detection, biomedicine, ...and light conversion devices, especially near-infrared-(NIR)-to-visible upconversion devices. In this research, a UCD that directly turned NIR light located at 1050 nm into visible light located at 530 nm was fabricated to investigate the underlying working mechanism of UCDs. The simulation and experimental results of this research proved the existence of the quantum tunneling phenomenon in UCDs and found that the quantum tunneling effect can be enhanced by a localized surface plasmon.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Developing low density and efficient dielectric loss materials has become a research hotspot, which can greatly meet the demands of modern radars and settle the problem of electromagnetic wave ...pollution. Herein, a series of N-doped ordered mesoporous carbon (OMC) materials with different nitrogen content were prepared via a modified self-assembly method and defect engineering in subsequent calcination treatment. It was discovered that the content and type of nitrogen doping can be effectively modulated by the amount of precursor dicyandiamide, resulting in the changes in porous structure, carbon defects, electromagnetic properties, microwave absorption (MA) performance and radar cross section (RCS) reduction values. Remarkably, as-fabricated OMC/N2.5 displays ideal MA performance, whose minimum reflection loss (RLmin) value reaches −35.3 dB at 7.76 GHz (3.0 mm) and its effective absorption bandwidth reaches 3.52 GHz (10.64–14.16 GHz, 2.0 mm). Furthermore, the optimal RCS reduction values can be obtained as 12.01 dB m2 when the detection theta is 30°, which validly reduces the chances of being detected by radar. Thus, this work opens up a novel way for the development of lightweight and high-efficiency MA materials.
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•The content and type of nitrogen doping can be modulated by the defect engineering, which can regulate MA performance.•The optimal RCS reduction value is 12.01 dB m2 (detection theta is 30°), reducing the chances of being detected by radar.•OMC/N2.5 achieves strong absorption (RLmin = −35.3 dB, 3.0 mm) and broad effective absorption bandwidth (3.52 GHz, 2.0 mm).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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