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On the Blue Emitting Phosphor Na <sub/>3</sub> RbMg <sub/>7</sub> (PO <sub/>4</sub> ) <sub/>6</sub> :Eu <sup>2+</sup> Showing Ultra High Thermal Stability
摘要： This work concerns a novel blue emitting LED phosphor activated by Eu2+. It turned out that this luminescent material can be efficiently pumped by near UV or UV-A radiation sources while it exhibits a high quantum yield for a doping level between 0.3 and 3.0%. More impressively, the material has a very high quenching temperature T1/2 and will thus be applicable on-chip in high power phosphor converted LEDs or even in laser diodes. The emission and thermal stability is almost identical to that of BAM:Eu2+ while the absorption band is broader and reaches into the near UV range. Therefore, Na3RbMg7(PO4)6:Eu2+ is a promising candidate as a blue emitter in high CRI full conversion LEDs. To investigate the site preference of Eu2+, DFT and Ligand Field Theory based calculations were performed to successfully predict the emission spectrum. An unusual decay behavior was observed at low temperatures and the underlying mechanism involving spin-forbidden transitions of Eu2+ is discussed.
关键词： high thermal stability,solid state lighting,Eu2+ luminescence,near UV LED,high CRI,decay time,Blue photoluminescence
更新于2025-11-21 11:18:25
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Origin of anisotropy and compositional dependence of phonon and electron transport in ZnO based natural superlattices and role of atomic layer interfaces
摘要： Reaction of ZnO with trivalent ions can form natural superlattice (SL) compounds, which possess unusual structural characteristics and strong anisotropic physical transport properties. In this work, by synthesizing strongly textured bulk polycrystals of pure SL phases and performing characterization and measurements for both in-plane and cross-sectional directions, we revealed the strongly crystal orientation dependent transport properties. The observed compositional or SL interface spacing dependent electrical conductivity is largely attributed to the overall doping of ZnO wurtzite regions. The atomic layer SL interfaces are phonon barriers, and the interfacial thermal (Kapitza) resistance depends on SL interface spacing. The transport direction perpendicular to these SL interfaces are electron-conductive paths with remarkably higher electron mobility. There are electron potential barriers associated with these atomic layer SL interfaces. The effective and absolute potential barrier heights are determined, which are proportional to the natural conduction band discontinuities. The current study provides new findings and knowledge about the role of SL interfaces in phonon and electron transport process in these ZnO based natural SLs. The present work can be useful and inspiring to design and modify complex layer-structured compounds, including synthetic superlattice systems, for a variety of applications where energy carriers transport is involved.
关键词： Interfaces,Superlattices,Electron potential barrier,Interfacial thermal (Kapitza) resistance,Thermal conductivity,ZnO
更新于2025-11-21 11:03:13
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Highly efficient rare-earth-free deep red emitting phosphor La <sub/>2</sub> Li <sub/>1?y</sub> Sb <sub/>1?x</sub> O <sub/>6</sub> : <i>x</i> Mn <sup>4+</sup> , <i>y</i> Mg <sup>2+</sup> : application in high-power warm w-LEDs
摘要： Phosphor-in-glass (PiG), which serves as both a luminescent convertor and organic encapsulation material in high-power white light-emitting diodes (w-LEDs), has become a prospective research hotspot owing to its high transparency and thermal stability. However, YAG:Ce3+ PiG-based LED devices still suffer from a lack of a red component. Therefore, the development of red phosphors with excellent quantum efficiency and superior thermal stability is urgent. Herein, a highly efficient La2Li1?ySb1?xO6:xMn4+,yMg2+ red phosphor with a broadband emission ranging from 670 to 720 nm was fabricated via a conventional solid-state reaction. By co-doping Mg2+ in La2LiSbO6:Mn4+, the emission intensity was enhanced significantly, which reaches as high as 10 times that of the single-doped La2LiSbO6:Mn4+. It is proposed that the Mg2+ dopant can compensate imbalanced charges for the substitution of Sb5+ by Mn4+ and interrupt adverse energy transfer among the Mn4+ activators. Impressively, a maximum quantum yield of up to 80.3% is achieved and about 80% emission intensity is retained at the temperature of 423 K. Furthermore, the crystal field strength (Dq) and Racah parameters (B and C) together with the nephelauxetic ratio (b1) were calculated based on the obtained spectroscopic data. By embedding the red-emitting La2LiSbO6:Mn4+,Mg2+ phosphor and yellow-emitting YAG:Ce3+ phosphor into TeO2-based glass, an inorganic PiG composite as a color converter to replace organic silicone was acquired. The excellent optical parameters and tunable chromaticity feature of the fabricated w-LEDs were achieved by adjusting the mass ratio of La2LiSbO6:Mn4+,Mg2+ to YAG:Ce3+ in the PiG plate, where the correlated color temperature changed from cool white (6555 K) to warm (4130 K) and the color rendering index increased from 73.7 to 86.6 under an operating current of 300 mA.
关键词： Phosphor-in-glass,quantum yield,red phosphor,Mg2+,thermal stability,w-LEDs,Mn4+
更新于2025-11-20 15:33:11
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Crosslink network and phenyl content on the optical, hardness, and thermal aging of PDMS LED encapsulant
摘要： This work aims to synthesize new series of polysiloxane copolymer through hydrosilylation reaction based on different level of crosslink densities and phenyl content. The results revealed that polysiloxanes resins with phenyl rings increased viscosity up to 3800 cps while displaying a relatively high refractive index of 1.531. The asymmetric phenyl substitution onto chain backbone led to formation of densely packed structure resulting in reduced water absorption and gas permeability of PDMS resins. High level of crosslinking contributed to a high shore A hardness and adhesion strength. It displayed transparency of 97% whose percentage reduction was 1.6% under thermal and 0.6% UV aging. No obvious discoloration was observed during accelerated thermal aging up to 210 min at 80 (cid:1)C. These results are key attributes that make the synthesized polysiloxane series as ideal candidate for high brightness LED encapsulant. ? 2019 Wiley Periodicals, Inc. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47895.
关键词： copolymers,thermal properties,ring-opening polymerization,optical properties,synthesis and processing techniques
更新于2025-11-19 16:56:42
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Deposition of gold nanoparticles upon bare and indium tin oxide film coated glass based on annealing process
摘要： We presented a simple and efficient strategy for deposition of gold nanoparticles (AuNPs) upon transparent bare and indium tin oxide (ITO) film coated glass substrate using gold colloids as Au sources. The method involved two steps: embedding in polyvinyl alcohol (PVA) film and annealing at high temperature. The AuNPs deposited on solid substrate because of migration and coalescence of gold at high temperature. The optical and structural properties of the AuNPs were characterised by UV-vis absorption spectra and scanning electron microscopy. The results indicate that the surface of AuNPs upon substrate was clean as annealing at 600 °C for 0.5 h. The size of AuNPs deposited on ITO glass increased with annealing time and volume of PVA-AuNPs. Meanwhile, the localised surface plasmon resonance peak of AuNPs deposited on substrate was also gradual red-shift. In addition, the size of AuNPs deposited on ITO substrate was larger than that on bare glass. This work provides a simple, low-cost and large-scale method for fabrication of substrate-based AuNPs, which is benefit for exploiting biosensors, photonic devices and optoelectronic devices.
关键词： thermal annealing,solid substrate,Gold nanoparticles,indium tin oxide film coated glass
更新于2025-11-19 16:56:35
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Complex Optical and Thermal Studies on As-Synthesized Conducting Polythiophene
摘要： A series of conducting polythiophene (PTh) samples have been synthesized using an in situ chemical oxidative polymerization technique in aqueous solution. The characterization of the as-synthesized optimized sample has been carried out by Fourier transform infrared spectroscopy, x-ray diffraction and thermogravimetric–differential thermal analysis techniques. Also, the complex optical parameters of all the as-synthesized polymeric samples have been investigated by using ultraviolet–visible spectroscopy. The as-synthesized polymeric samples exhibited absorption around 220–280 nm. The optical band gap was found to ranges from 5.06 eV to 5.24 eV. The maximum optical conductivity for the sample with a stoichiometric ratio of thiophene to FeCl3 of 70:30 wt.% was found to be 5.973 9 108 S cm?1 at 280 nm. The experimental results reveal that the thermal and optical performance of conducting PTh can be dramatically enhanced for the sample with a stoichiometric ratio of thiophene to FeCl3 of 70:30 wt.%. The improved complex optical properties of as-synthesized samples of conducting PTh validate their potential utilization in optoelectronic devices.
关键词： thermal analysis,complex optical properties,Polythiophene
更新于2025-11-19 16:56:35
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Improvement of Optical and Thermal Properties for Quantum Dots WLEDs by Controlling Layer Location
摘要： The inorganic halide perovskite quantum dots (QDs) have been considered as a promising substitute for white light-emitting diodes (WLEDs). In this article, the green CsPbBr3 QDs and red K2SiF6:Mn4+ (KSF) phosphor were used to fabricate the conversion layers. Because the layers location is fundamental to the absorption priority of blue light, the location of KSF and QDs were controlled and the QDs-up type and QDs-down type WLEDs were made. The optical power, luminous efficiency, CCE and luminous intensity in the middle of QDs-up type are 13.83 mW, 13.54 lm/W, 11.94% and 2.65 cd, meaning 24.26%, 25.72%, 2.63% and 23.83% higher than those of QDs-down type, respectively. In addition, the QDs-up type has a lower correlated color temperature (CCT) shift of 734 K and a decreased highest temperature of 56.8℃ (51.5% and 14.9% lower). These key property differences indicate that the QDs-up type is more suitable for the application in display and backlight. In order to explore the reasons for these differences, the emission spectra, CCE, reflection rate, absorption rate and temperature curves of QDs or KSF films were also analyzed, which provided a better understanding of designing package structures.
关键词： layer location,thermal properties,quantum dots WLEDs,optical properties
更新于2025-11-19 16:46:39
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[Lecture Notes in Mechanical Engineering] Advances in Thin Films, Nanostructured Materials, and Coatings (Selected Papers from the 2018 International Conference on “Nanomaterials: Applications & Properties”) || Stain Effect on the Properties of Polar Dielectric Thin Films
摘要： Low cost scalable processing and substrates are critical for optimized polar dielectric performance of functional oxide thin ?lms if they are to achieve commercialization. Here, we present a comprehensive investigation of the role low-cost MgO, Al2O3, SrTiO3 and Si substrates on the structural and electrical properties of sol-gel derived SrTiO3 (ST) and K0.5Na0.5NbO3 (KNN) thin ?lms. The substrate is found to have a strong effect on the stress/stain state and, consequently, on the dielectric and ferroelectric response of the ?lms. A tensile stress induced in-plane by the thermal expansion mismatch between the substrates and the ?lms observed for ST and KNN ?lms deposited on platinized Al2O3 and Si substrates, respectively, lowers the relative permittivity and remanent polarization values in the parallel plate capacitor geometry. In contrast, a compressive stress/strain observed for ST ?lms deposited on MgO/Pt and KNN ?lms on SrTiO3/Pt substrates result in superior polarization and dielectric permittivity, corresponding to enhanced out-of-plane displacement of Ti4+ ions in ST ?lms and Nb5+ ions in KNN ?lms. It is thus demonstrated that for polycrystalline polar dielectric thin ?lms the relative permittivity and polarization may be optimized through an induced compressive stress state.
关键词： Dielectric properties,Sol-gel,Thin ?lms,Stress/strain,Thermal expansion,Ferroelectric hysteresis
更新于2025-11-14 17:28:48
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A Wide Temperature Insensitive Piezoceramics for High-Temperature Energy Harvesting
摘要： One of the key challenges in the development of high-temperature energy harvesting (HTEH) technology is to clarify the relationship between temperature-dependent material parameters and device power generation capabilities. However, at present, the research on temperature stability of piezoceramics mainly relies on thermal annealing technology, which cannot follow the actual temperature dependence of the piezoelectricity, and it is even more difficult to predict the temperature stability of HTEH. To shed light on this field, here, (1-x)BiScO3-xPbTiO3 system was chosen for building HTEH material, and the temperature dependent electrical parameters, such as d33, εr, and g33, have been measured by multiple in-situ techniques. It was found that the synergistic effect of d33 and εr with temperature helps to obtain a stable g33 value in a wide temperature range. Moreover, in the mode of the cantilever-type energy harvester, a stable output voltage was obtained at x=0.64 harvester with less than 20% change over a broad temperature range of 100-250 oC, and it was verified that the temperature stability of g33 is crucial to the operation stability of HTEH devices.
关键词： in-situ techniques,piezoelectric materials/properties,energy harvesting,thermal properties
更新于2025-11-14 17:28:48
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Conductive electrodes based on Ni–graphite core–shell nanoparticles for heterojunction solar cells
摘要： Ni–graphite core–shell nanoparticles (CSNPs), which consisted of Ni nanoparticles (NPs) wrapped with several graphene layers, were grown by the thermal reduction of NiO NPs using H2. The effect of the synthesis temperature (800, 900, 1000, and 1100 °C) on the formation of multilayer graphene shells on the Ni core NPs was investigated to evaluate the structural and electrical characteristics of the particles. The proposed chemical reactions for the formation of Ni NPs can be summarized as follows: formation of liquid Ni by the reduction of NiO, thermal decomposition of the NiO phase, and formation of multilayer graphene shell because of the supersaturation of C in the liquid Ni phase. The resistivity of the electrode pattern fabricated with the Ni–graphite CSNP paste was found to be 6.75 × 10?3 ?·cm. Further, the power conversion efficiency of bulk heterojunction solar cells fabricated with the Ni–graphite CSNPs is higher than that of cells fabricated without the Ni- graphite CSNPs. Thus, our Ni–graphite CSNPs can be employed as a highly efficient electrode material in bulk heterojunction solar cells.
关键词： Thermal reduction,Core–shell structure,Nickel oxide nanoparticle,Graphite,Graphene
更新于2025-11-14 17:04:02