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Inspired by the double-helix structure of biological DNA, low-volume fraction and high-strength Al 2 O 3 twisted honeycomb structures with characteristics similar to those of helical structures in the z -axis were prepared by digital light processing 3D printing technology. As the twist angle increased, the compressive strength of the fabricated Al 2 O 3 structure decreased, and the deformation mechanism of the Al 2 O 3 structures gradually changed from stretching-dominated to bending-dominated, which can be predicted by the Gibson–Ashby model. The relationship between the effective elastic modulus and the volume fraction that can be modified by varying the wall thickness was described by the Pabst–Gregorova exponential relationship. The compressive strength of the Al 2 O 3 structure with a twist angle of 0° can reach 62.4 MPa at a volume fraction of 13.3%, providing guidance to optimize lightweight structures of ceramics. [ABSTRACT FROM AUTHOR]

Digital light processing 3D printing can be applied to fabricate complex silicon nitride (Si 3 N 4) components. However, because of the surface hydroxyl groups and large refractive index, it is still a foremost challenge to realize a stable photosensitive Si 3 N 4 slurry with combined benefits of low viscosity and large curing depth. In this study, we propose a new formulation strategy to prepare Si 3 N 4 slurry. Starting from the optimization of monomer ratio, we have systematically optimized powder particle size, dispersant and photoinitiator on the rheological properties and curing properties of Si 3 N 4 slurry. Specifically, we have fabricated a stable photosensitive Si 3 N 4 slurry (48 vol%) with a viscosity of 2.09 Pa s (30 s−1), a critical curing energy of 126.09 mJ/cm2 and a maximum curing depth of 80 µm. Finally, based on this optimized slurry, we have successfully obtained complex Si 3 N 4 green body with no defect, which demonstrates great potential to fabricate arbitrary complex ceramic components for various applications. [ABSTRACT FROM AUTHOR]

Nano-SiO 2 porous thermal insulating material (TIM) has drawn tremendous research interests due to its advantages of low density, high porosity and low thermal conductivity. However, its long-term stability in humid environment can be severely deteriorated by the high hydrophilicity resulting from tetrahedral coordination of oxygen and capillary effect of porous structure. It is still a great challenge to cost-effectively fabricate bulk TIM with superior hydrophobicity and consequent remarkable self-cleaning capability. Herein, via an oil-in-water microemulsion treatment, we have proposed a new strategy to construct 3D superior hydrophobic nano-SiO 2 porous TIM. The polymethylhydrosiloxane-modified TIM exhibits a large water contact angle of 166°, and corresponding excellent self-cleaning characteristic while maintaining low thermal conductivity of 0.031 W/m·K. Moreover, our high hydrophobicity of TIM exhibits excellent durability under high temperature up to 400 °C, high humidity of 100%, and chemical erosions. Detailed knowledge of the physical chemistry basis of the superior hydrophobic nano-SiO 2 porous TIM can provide great opportunity to fabricate advanced self-cleaning and heat insulating devices especially targeted for harsh environments. [ABSTRACT FROM AUTHOR]

Regarding advanced 5G mobile communication, microwave dielectric ceramics are considered as the most potential materials to develop new-generation base station resonators. Herein, ZnNb 2 O 6 ceramics with ε r of approximately 24 have been prepared using the solid-state reaction method, with tailored extra ZnO of x mol% (x = 1, 2 and 3). We have for the first time applied the P-V-L chemical bond theory to investigate ZnNb 2 O 6 ceramics with ZnO doping, by exploring the relationship of dielectric properties and chemical bond characteristics. Particularly, the Raman spectra demonstrates that the full width at half maximum of υ 1 (A g) vibration mode can exhibit significant correlation with the quality factor (Q × f). To further support the experimental study, we have also conducted the first-principle calculation of electron density difference via CASTEP package, which further confirms the change of temperature coefficient of resonance frequency (τ f). Our newly designed ZnNb 2 O 6 ceramics doped with 1 mol% ZnO exhibit excellent dielectric properties, i.e., ε r = 23.74, Q × f = 102,824 GHz and τ f = −55.38 ppm/°C, which demonstrates great potential to construct miniaturized 5G base station with advanced ceramic dielectrics. [ABSTRACT FROM AUTHOR]

We have optimized a CuO-doped silver paste to significantly improve the adhesion strength of silver thick film on AlN ceramic substrate, which can be widely applied in power electronic packaging applications. Via a combination of scanning electron microscope and X-ray diffraction, we have systematically studied the silver layer morphology on top of AlN ceramic substrate, and the interphases between the silver thick film and AlN substrate. Due to the CuAl 2 O 4 intermediate formed at the silver layer/AlN interface, the adhesion strength of silver thick film can be greatly improved. Particularly, the silver paste with 3 wt% nano-CuO sintered on AlN ceramic substrate exhibits high adhesion strength of 15.3 MPa with good electrical conductivity of 0.9 mΩ/□. [ABSTRACT FROM AUTHOR]

Ceramics joining has been widely applied in MEMS sensors, microwave and imaging devices as well as other ceramic packaging applications to fabricate multifunctional ceramic components. In this study, a glass frit with gradient thermal expansion coefficient (TEC) has been applied as the bonding material to join the ceramic of Al 2 O 3 and AlN. This glass frit consists of two types of glasses with different TEC. The Al 2 O 3 and AlN ceramics have been successfully joined with this glass frit in muffle furnace at 850 °C for 1 h. The bonding strength of Al 2 O 3 /AlN ceramic joined via this glass frit exceeds 40 MPa without any cracks in the joining interface, which is much superior compared with that of conventional glass frit bonding. Our work demonstrates that the gradient-TEC glass frit bonding is an effective method to join different types of ceramics. [ABSTRACT FROM AUTHOR]

PbO–ZnO–B 2 O 3 (PZB) glass with low-melting temperature has been widely applied in microelectromechanical systems (MEMS) packaging. However, the high thermal expansion coefficient (TEC) of PZB glass usually leads to strict packaging requirements. Here, in order to achieve ideal TEC, we have introduced β -eucryptite into PZB/ β -eucryptite composite glass and optimized the composite fabrication process. Firstly, PbO:ZnO:B 2 O 3 in mol ratio of 65:15:20 was selected as glass matrix owing to its low-melting temperature and good wettability. Then, β -eucryptite ceramics with ultra-low TEC were synthesized via a facile solid-state reaction method to optimize subsequent composite TEC value. The combination of corresponding material and device characterizations suggest that the pure phase and regular columnar grains of β -eucryptite ceramic can be obtained by sintering at 1450 °C for three hours, which can result in the lowest negative TEC of α 30-300°C = −10.74 × 10−6 K−1. Furthermore, regarding the PZB/ β -eucryptite composite glasses, systematic experiments demonstrated that the β -eucryptite introduction can greatly impact the TEC of matrix glass with only negligible effect on the softening point (T s). Importantly, composite glasses with TEC of α 30-300°C = 3.26 × 10−6 K−1, T s = 380 °C and wetting angle < 30° are ideal for MEMS packaging. This work implements optimized fabrication process to obtain low-melting PZB/ β -eucryptite composite glasses with ideal TEC values, which can be envisaged to be applied in advanced MEMS packaging applications. [ABSTRACT FROM AUTHOR]

Highly efficient CaSi2O2N2:Eu2+ green phosphors were synthesized via solid-state reaction method. The produced phosphors are effectively excited with UV-vis light of wavelength between 300 and 460 nm and emit a single, intense, and broad emission band centered at 538 nm. The experimental results and their analysis suggest that the energy transfer mechanism should occur due to dipole-dipole interactions among Eu2+ ions, resulting in a shift in emission spectrum toward longer wavelengths with increasing Eu2+ concentration. The quenching concentration of Eu2+ (i.e., where the emission intensity maximizes) is approximately 2 at. %. Accordingly, the produced CaSi2O2N2:Eu2+ green phosphors are qualified for further consideration and experimentation for potential use in white light emitting diodes. [ABSTRACT FROM AUTHOR]

Herein, a bio-based plasticizer ketalized tung oil butyl levulinate (KTBL) was developed using methyl eleostearate, a derivative of tung oil, and butyl levulinate. KTBL can be used as an auxiliary plasticizer to partially replace traditional plasticizer. The plasticizer has a ketone structure, an ester base, and a long linear chain. It was mixed with dioctyl phthalate (DOP), and the effect of the plasticizer KTBL as an auxiliary plasticizer on the plasticization of poly(vinyl chloride) (PVC) was studied. Their compatibility and plasticizing effect were evaluated using dynamic–mechanical thermal analysis (DMA), mechanical property analysis, and thermogravimetric analysis (TGA). The results demonstrate that when the KTBL to DOP ratio is 1:1, the blended sample with KTBL exhibits superior mechanical performance compared to pure DOP, resulting in an increased elongation at break from 377.47% to 410.92%. Moreover, with the increase in KTBL content, the durability is also significantly improved. These findings suggest that KTBL can serve as an effective auxiliary plasticizer for PVC, thereby reducing the reliance on DOP. [ABSTRACT FROM AUTHOR]

Abstract Ca 0.66 Ti 0.66 Nd 0.34 Al 0.34 O 3 (CTNA) ceramics were prepared by solid-state reaction method and their sintering behavior, microwave dielectric properties, and microstructure were investigated. CTNA ceramics were examined by Raman scattering to reveal the correlation of perovskite structure with the microwave properties. It found that the area of peak A 1g (O) stretch mode reflects the quality factor Q × f value in the perovskite materials. This concludes that the oxygen octahedron plays an important role of the material's microwave performance. Sintering temperature affected the unit cell volume and the lattice parameters of the CTNA ceramics, the grain size distribution, the Gibbs free energy, the thermal expansion coefficient (CTE), and the dielectric properties (ε r , Q × f , τ f). The samples sintered at 1500 °C displayed the best dielectric constant and Q × f , as 44.94 and 41922.22 GHz, respectively. Highlights • The CTNA ceramics were sintered at different temperatures were investigated. • The thermal analysis detailed description of the stages of sintering process. • The unit cell volume is affected by the sintering temperature was confirmed by XRD. • Raman to reveal the correlation of structure with the microwave properties. • Relationship between grain size, Gibbs free energy, CTE, and dielectric properties. [ABSTRACT FROM AUTHOR]

The influence of BaO content (up to 15 mol%) on the crystallization behaviour, structure, thermal properties and microwave dielectric properties of the BaO-CaO-B 2 O 3 -SiO 2 glasses and glass-ceramics system was investigated. The glasses were produced by melting at 1400 °C and quenching into water, and the glass-ceramics were produced via heat treatment at temperatures between 750 and 800 °C. The results of X-ray diffraction analysis showed that increasing the BaO content raised the resistance of the glass against crystallization and favoured the transformation of β-CaSiO 3 and α-CaSiO 3 phases, which crystallized in the Ba-free and in low BaO content compositions, into SiO 2 and Ba 4 Si 6 O 16 , which crystallized in compositions with higher concentrations of BaO. The BaO content had little influence on the glass transition temperature ( T g ) and the linear coefficient of thermal expansion (CTE), but strongly reduced the softening point ( T s ). Even the addition of BaO as minor additives resulted in a dramatic reduction of the T s ; for example, the T s decreased from 902 °C for the Ba-free composition to 682 °C for the BaO-containing one (5%). Low values of the dielectric constant (5.9 ≤  ε r ≤ 6.63) and dielectric loss (1.12 × 10 −3 ≤ tan δ  ≤ 3.15 × 10 −3 ) were measured. [ABSTRACT FROM AUTHOR]

A novel method for preparing aluminum/aluminum nitride ceramics (Al/AlN) substrates is proposed in this paper. The method included two processes: (1) the surface of AlN was coated with a CuO thick film and sintered; (2) Al foil was put on the pretreated (in process 1) AlN surface and bonded to AlN through pre-heating at 400 °C and final heating at 660 °C in N 2 -H 2 reduction atmosphere. The experimental results obtained by optical and scanning electron microscope (SEM) observations as well as by X-ray diffraction analysis at the cross-sections of the joints and the fracture surfaces, suggest that the reaction mechanism starts with the reaction of CuO with AlN to form CuAlO 2 , when the AlN coated with CuO is heat-treated at high temperature. A Cu layer is produced by the reduction of CuO and Cu diffuses in the Al foil, forming strong Al/AlN joints. Elongated crystals of Al 2 Cu are developed in the reaction zone at the interface between Al and AlN. The results of mechanical tests showed that the peeling-off strength of the Al foil from the surface of the AlN substrate reached a value of 15.4 MPa for the Al/AlN couples produced after 30 min of heat treatment at 660 °C. [ABSTRACT FROM AUTHOR]

The influence of substitution with rare earth elements in orthorhombic Ca 0.66 Ti 0.66 R 0.34 Al 0.34 O 3 (R = Sm, Nd, La) perovskite ceramics, which were successfully produced with a solid-state reaction method, on their crystal structure (analyzed with Rietveld refinement of X-ray diffractograms and Raman spectroscopy) and on the microwave dielectric properties was investigated. The dielectric constant (ε r ) increased due to the increase of cell volume, which was a result of the increase of the ionic radius of the rare earth cations incorporated in the host lattice R 3+ . The values of the quality factors were 43620.74, 41292.71, and 38389.57 GHz for the Sm-, Nd-, and La-containing ceramics, respectively. The decrease of these values is correlated to the level of distortion of the octahedral due to the incorporation of the three different rare earth cations. The temperature coefficient of resonant frequency increased from 4.99 for the Sm-ceramics to 9.92 ppm/ ° C for the La-ceramics, attributed to the increase of cell polarization. [ABSTRACT FROM AUTHOR]

Perovskite ceramics with a formula of Ca 0.7 Ti 0.7 La 0.3 Al 0.3 O 3 (CTLA) were produced through a conventional solid-state reaction procedure following three different La 3+ -doping methods using powders of La 2 O 3 , or La 2 O 3 /Al 2 O 3 powder mixture, or LaAlO 3 . La 3+ doping favored grain growth and densification, affected the grain size distribution, and improved the dielectric properties of the produced sintered CTLA ceramics. The doping methods had a strong influence on these properties. More specifically, doping with La 2 O 3 and La 2 O 3 /Al 2 O 3 resulted in formation of solid solution, while a secondary phase formed in the CTLA ceramics doped with LaAlO 3 , which caused a coarsening of the microstructure and lowered the La 3+ doping effects on the dielectric properties. The experimental results suggest that La 3+ doping improves the dielectric properties of the sintered CTLA perovskite ceramics, which are further enhanced by doping with Al 3+ ions in small amounts. However, further increase of Al 3+ ions content jeopardizes them. [ABSTRACT FROM AUTHOR]

Ca 0.66 Ti 0.66 Sm 0.34 Al 0.34 O 3 (CTSA) ceramics were produced using a solid-state reaction method, and their sintering behavior, microwave dielectric properties, and microstructure were investigated. Sintering temperature affected the unit cell volume and the lattice parameters of the CTSA ceramics as well as the grain size distribution, the Gibbs free energy, the thermal expansion coefficient (CTE), and the dielectric properties (ε r , Q×f, τ f ). The samples sintered at 1500 °C displayed the best dielectric constant and Q×f, as 42.49 and 46069.86 GHz, respectively. [ABSTRACT FROM AUTHOR]

BaO-Sm 2 O 3 -5TiO 2 (BST5) ceramics with NdAlO 3 additions of up to 15 wt% were produced with a solid state reaction method, and their structural and microwave dielectric properties were determined. Experimental results showed that NdAlO 3 neither merged nor altered the orthorhombic tungsten bronze structure of the main phase of the produced ceramics (except for a shrinkage in the crystal lattice), but it was segregated in distinct grains in the microstructure of the produced ceramics. However, the amount of NdAlO 3 strongly influenced the densification and the microstructure (i.e. grain shape and size) of the produced ceramics. Analysis of the experimental results suggests that the microstructural features can be correlated to the dielectric properties of these ceramics. Accordingly, the dielectric constant (ε r ) and the temperature coefficient of resonant frequency (τ f ) of the produced BLT5 ceramics can be tuned with the amount of NdAlO 3 additions and the sintering process parameters. The best dielectric properties were achieved for BaO-Sm 2 O 3 -5TiO 2 ceramics with 7.5% NdAlO 3 (ε r =73.22, Q×f =10,300 GHz, and τ f =−1.05 ppm/°C). [ABSTRACT FROM AUTHOR]

Surface metallization of aluminum nitride is performed by a reactively thick film method. A layer of copper film is deposited on the surface of AlN ceramics. The morphology and composition of the metalized copper layer on ceramic substrate were investigated via scanning electron microscope (SEM) and X-ray diffraction (XRD). The interface layer between copper film and AlN substrate was examined through SEM, XRD and EDS. Reaction phases, Cu 2 O and intermediate phases (CuAlO 2 and CuAl 2 O 4 ), were detected at the interface layer. Subsequently, the formation process of these phases at the interface layer was discussed. And consequently, the relation within reaction phases and bonding strength was observed. Reaction phases play a key role in increasing bonding strength. The effect of these phases such as Cu 2 O and intermediate phases (CuAlO 2 and CuAl 2 O 4 ) on the mechanical property was discussed. Results show that the presence of Cu 2 O particles are detrimental to bonding strength. However, spinel CuAl 2 O 4 and isolated CuAlO 2 laminates at the interface layer can increase the bonding strength. The experimental results suggest that this thick film method is a useful technology for various metal-ceramics bonding. [ABSTRACT FROM AUTHOR]

A series of Eu-doped LaSr 2 AlO 5 phosphors were synthesized by high-temperature solid state reactions under oxidative and reductive atmospheres, respectively. The photoluminescence properties, fluorescence quenching mechanism and valence-change behavior of europium ions in the phosphor have been studied. For the samples prepared in oxidative atmosphere, the Eu 3+ ions occupy the La 3+ sites and exhibit characteristic sharp lines(500–750 nm) originating from the 5 D 1 and 5 D 0 levels to 7F transitions. With the increase of Eu 3+ concentration, the chromaticity coordinates of La 1− x Sr 2 AlO 5 : x Eu 3+ phosphors are turned from (0.479, 0.453) for x =0.005 to (0.621, 0.358) for x =1.0. The quenching process of 5 D 1 → 7 F 1 (533 nm) emission is attributed to cross-relaxation as the Eu 3+ concentration reaches 5 mol%. The dominant line emission 5 D 0 → 7 F 2 (619 nm) is quenched due to the exchange interaction as the Eu 3+ concentration reaches 75 mol%. For the sample prepared in reductive atmosphere, it shows the presence of both Eu 3+ and Eu 2+ . The Eu 2+ in LaSr 2 AlO 5 host lattice can be excited by a blue light with an intense broad red emission band centered at 610 nm (a full width at half maximum of 110 nm) with color coordinates of (0.611, 0.368). The internal quantum efficiency was measured to be ~42%, indicating that this phosphor has a great potential in blue-chip pumped white light emitting diodes (WLEDs). The conditions for the reduction process of Eu 3+ to Eu 2+ in solid state compounds were discussed. From the X-ray diffraction and Gaussian fitting of the emission spectra, we propose that Eu 3+ ions occupy the La 3+ sites while Eu 2+ ions occupy the two different Sr 2+ sites. [ABSTRACT FROM AUTHOR]

Abstract: The production of composites of epoxy molding compounds (EMCs), which can feature a good balance between thermal conductivity and flame-retardant behavior in terms of flammability and burning behavior, was achieved by incorporating high thermal conductivity Si3N4 and flame retardant Al(OH)3 (ATH) fillers in the epoxy matrix. The experimental results were obtained from thermal conductivity measurements and limiting oxygen index (LOI) and UL-94 tests. These results showed that the Si3N4 filler has a great influence on thermal conductivity, which markedly increased for Si3N4 volume fractions >40%, whereas the ATH filler greatly improved the flame resistance of EMCs. The simultaneous presence of both Si3N4 and ATH fillers in the EMCs positively influenced both properties. The aim of this study was to produce composites suitable for electronic packaging applications: an optimum combination of the two fillers was determined for a total volume fraction of fillers in EMC of 60vol.% and a volume ratio of Si3N4:ATH at 3:2; this composite had a thermal conductivity of 2.15W/mK, an LOI of 53.5, and a UL-94 vertical burning test ranking of V-0. [Copyright &y& Elsevier]

Abstract: Single-phase broad-band red-emitting Ca3Si2O7:Eu2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H3BO3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603nm, a full width at half maximum of 110nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01mol Eu2+. The discussion of the results shows that Eu2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ∼31Å. [Copyright &y& Elsevier]

Abstract: CaSi2O2N2 phosphors co-doped with Ce3+ and Eu2+ was synthesized via solid-state reaction method. The experiments aimed at optimizing the composition of those phosphors for achieving the highest luminescence intensity as well as at shedding light in the mechanism that governs their luminescence behavior. The overlap of the blue emission spectrum due to Ce3+ with the yellow excitation spectrum due to Eu2+ suggests resonance-type energy transfer mechanism from Ce3+ to Eu2+ taking place in the CaSi2O2N2 host lattice, where electric dipole–dipole interactions dominate. The properties of the produced phosphors qualify them for further consideration in the technology of white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: Ce3+/Eu2+ co-doped Li2SrSiO4 phosphor yields two emission bands consisted of blue and yellow components, which shows great potential as single host white phosphor for white LEDs. Effective energy transfer occurs in Ce3+/Eu2+ co-doped Li2SrSiO4 due to large spectral overlap between the emission of Ce3+ and excitation of Eu2+. Co-doping of Ce3+ enhances the emission intensity of Eu2+ greatly by transferring its excitation energy to Eu2+. The Ce3+ →Eu2+ energy transfer, thoroughly investigated by their absorption, excitation and photoluminescence decay behaviors, is demonstrated to be in the mechanism of electric dipole–dipole interaction. [Copyright &y& Elsevier]

Abstract: Applications insulated metal substrates (IMS) for high-density and high-power mounting are greatly extending with miniaturizing of electronic components. Recently, aluminum nitride film has been used as a potential insulator and/or passivation material in insulated metal substrate because of its high intrinsic thermal conductivity, low thermal expansion coefficient, low dielectric constant and high electric resistivity. In this investigation, AlN films were deposited on Al substrates by radio frequency (RF) reactive magnetron sputtering. The metal-interfacial insulator layer-metal (Al/AlN/Al MIM) structures were obtained with AlN layer on Al substrates. Electrical properties of the MIM structures were investigated by meaning of C–V and C-f characteristics in the frequency range of 100Hz–500kHz and voltage range of −4 V to 4 V. Experimental results show that the dielectric constant of this structure decreases gradually with increasing frequency. While the dielectric loss tangent was tested from low frequency to high frequency, it is found that the dielectric loss tangent decreases from 0.03375, reaches a minimum (0.00424) at approximately 65kHz and then increases sharply. These results are in accordance with modified model of Goswami and Goswami for such structure. The dielectric dispersion is observed due to distribution of interface states as well as ionized space charge carriers such as the oxygen atoms, nitrogen vacancies and defects. The AC conductivity results show that the electrical resistance decreases as the frequency increasing due to hopping type conduction. [Copyright &y& Elsevier]

Abstract: Eu2+ and Mn2+ co-doped SrSi2O2N2 green-phosphors, with promising luminescent properties (examined by their powder diffuse reflection, photoluminescence excitation and emission spectra) suitable for UV converted white LEDs, were produced by high temperature solid-state reaction method. The produced materials exhibited intense broad absorption bands at 220–500nm and a broad emission band centered at ca. 530nm, attributed to 4f–5d transitions of Eu2+. The emission intensity of Eu2+ ions was greatly enhanced by introducing Mn2+ ions into SrSi2O2N2:Eu2+ due to the energy transfer from Mn2+ to Eu2+. The energy transfer probability from Mn2+ to Eu2+ depends strongly on the Mn2+ concentration, which is maximized at a Mn2+ concentration of 3mol%. It drastically decreases for higher concentrations. The results indicated that SrSi2O2N2:Eu2+, Mn2+ is a promising green-emitting phosphor for white-light emitting diodes with near-UV LED chips. [Copyright &y& Elsevier]

Abstract: Divalent europium-activated strontium orthosilicate Sr2SiO4:Eu2+ and Mg0.1Sr1.9SiO4:Eu2+ phosphors were synthesized through the solid-state reaction technique. Their luminescent properties under ultraviolet excitation were investigated. The X-ray diffraction (XRD) results show that these phosphors are of α′-Sr2SiO4 phase with a trace of β-Sr2SiO4. Doping of Eu2+ ion into the crystal lattice results in the lattice constant being expended, while Mg2+ makes the lattice constant shrinking. A solid solution with the same crystal structure is formed when Eu2+ or Mg2+ substitutes part of Sr2+ ions and occupies the same lattice sites. The Sr2SiO4:Eu2+ phosphors show two emission spectra peaked at 535 and 473nm originated from the 5d–4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. By substitution of 0.1mol of Sr2+ with Mg2+, these two emission bands are tuned to be in the blue and yellow region (459 and 564nm for Mg0.1Sr1.88SiO4:Eu0.02), respectively. The tuning effect is discussed. With a combination of the blue and yellow emission bands the phosphors show white color, indicating that these phosphors may become promising phosphor candidates for white light-emitting diodes (LEDs). [Copyright &y& Elsevier]

Abstract: A kind of polymer composite was fabricated using polystyrene as the matrix and Si3N4 powder as filler employing the method of heat press molding. Microstructure, thermal conductivity and dielectric constant of the Si3N4 filled composite were evaluated. The effect of the volume fraction of Si3N4, the particle size of the polystyrene matrix and the silane treatment of Si3N4 filler on the thermal conductivity of the composite was investigated; dielectric constant of the composite was evaluated. The main factors that affect the thermal conductivity of the composite were confirmed through theoretical analyzing of the experimental data and the thermal conductivity model. Experimental results show that with the filler content increasing, a thermally conductive network is formed in the composites, thus the thermal conductivity of the composite increases rapidly. The composites experience a highest thermal conductivity of 3.0W/mK when the volume fraction of the filler reaches 40%. The increasing of thermal conductivity is dominated by the ease of forming a thermal conductive network. A larger polystyrene particle size, a higher Si3N4 filler content and the silane treatment of the filler have a beneficial effect on improving the thermal conductivity. The dielectric constant increases with the content of Si3N4 filler, however, it remains at a relatively low lever (<4, at 1MHz). [Copyright &y& Elsevier]

Abstract: Aluminium nitride (AlN) powders were prepared by self-propagating high-temperature synthesis (SHS). Aluminium and AlN powder mixtures with weight ratios of about 60:40, in the absence and in the presence of 3-wt.% NH4F and 3-wt.% NH4F+3-wt.% carbon powders as additives were ignited in a nitrogen atmosphere of 8 MPa. Highly crystalline AlN particles with regular hexagonal morphology were obtained in the presence of 3-wt.% NH4F+3-wt.% carbon. The microstructure development during the reaction and the influence of these additives were determined by SEM/EDS and XRD analysis of the resulting products. A mechanism for the formation of AlN with a regular hexagonal morphology has been suggested. [Copyright &y& Elsevier]

Abstract: Porous sialon ceramics have been cost-effectively prepared by pressureless sintering from a mixture of elongated SHS β-sialon powders with an α-sialon precursor composition composed of α-Si3N4, AlN, Y2O3 and Al2O3. The obtained porous sialon ceramics exhibited low shrinkage and homogeneous pore size distribution. The results of X-ray diffraction and scanning electron microscopy showed that a uniform microstructure with elongated and intermingled β-SiAlON grains, which were strongly connected by α-SiAlON phase, has been obtained. [Copyright &y& Elsevier]

Reaction sialon suspensions were prepared using 3-wt.% KD1 (a polyester/polyamine condensation copolymer) as dispersant in organic media of 60-vol.% methyletheylketone and 40-vol.% ethanol. Different homogenizing procedures were used and compared, such as: high energetic planetary milling, low energetic ball milling and ultrasonic disaggregation. The effect of different homogenizing routes and solids loading on the rheology of suspensions and on the properties of slip casting green bodies has been studied. The differences observed among the various mixing procedures could be attributed to the different degrees of disaggregation and therefore to different fractions of surface coverage of the reaction sialon powders by the dispersant. [Copyright &y& Elsevier]

For new-generation miniaturized and high-frequency electronics, it is of vital importance to develop advanced electronic packaging materials, which combine high electromagnetic interference (EMI) shielding effectiveness (SE) and efficient thermal management capabilities, including heat absorption, thermal conductivity (TC) and heat dissipation. However, high EMI SE and efficient thermal management usually cannot complement each other for the same packaging material, because EMI shielding devices convert electromagnetic radiation directly into heat consumption, leading to consequent severe challenge to dispose heat dissipation. Herein, we have newly developed a high-performance phase change composites, in which MXene is confined in shape-stabilized phase change material (PCM) for simultaneous achievement of high EMI SE and efficient thermal management. Regarding high EMI, MXene can effectively shield electromagnetic radiation by converting the radiation into heat consumption. As for thermal management, PCM enables efficient heat absorption via the phase change process, and MXene enhances the thermal conductivity (TC) of MXene/PCM composite to facilitate heat dissipation. As a result, our developed MXene/PCM composite can achieve a high EMI SE of 64.7 dB in X-band, with an improved TC of 0.74 W/m·K. Furthermore, the interlayer capillary effect of MXene inhibits the leakage of liquid PCM during the solid-liquid phase transition, which can maintain the PCM shape stability. Our newly-designed shape-stabilized MXene/PCM composites with high EMI SE and large TC shed new light on designing EMI shielding materials with prolonged exposure to electromagnetic radiation, which can be envisioned to exhibit vast implications for advanced new-generation miniaturized and high-frequency electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

• B-site precursor method can effectively inhibit the appearance of second phase. • B-site precursor method can obtain high reactivity Mg 4 Nb 2 O 9 powders. • B-site precursor method can promote integrality of the crystal structure. Mg 4 Nb 2 O 9 ceramics have been prepared by B-site precursor method in this work. Experimental results demonstrate that the uniform particles-size distribution of Mg 4 Nb 2 O 9 powders can be obtained, which exhibit high reactivity to promote the grain growth of Mg 4 Nb 2 O 9 ceramics. Moreover, the Mg 4 Nb 2 O 9 ceramics via B-site precursor method can be sintered at a wide range of sintering temperature from 1275 to 1375 °C with single phase Mg 4 Nb 2 O 9 composition and high crystallinity. Compared to the conventional solid-state method, the Mg 4 Nb 2 O 9 ceramics prepared by B-site precursor method exhibit excellent Q × f value by above 168,756 GHz. [ABSTRACT FROM AUTHOR]

The strong covalent bonding of SiC makes it difficult to be fully sintered using conventional sintering techniques. Therefore, electrical current-assisted sintering techniques such as spark plasma sintering are needed to sinter SiC. The finite numerical simulations have been generally used to predict and guide sintering processes of ceramics (i.e.TiC,AlO 3). In this work, the numerical simulations of the temperature distribution, electrical field and thermal field on the porous SiC cylindrical samples by Comsol were investigated in details. The influence of porosity on the temperature distribution and electrical field distribution of the SiC samples were analyzed. Both the maximum current density (1.19 × 107A/m2) and the maximum temperature (2030 °C) of the SPS device occurred at the punch/spacer interface. The temperature values at the centre of the samples were proportional to the porosity, and the temperatures at the center of the samples increased from ∼1960 °C to ∼2010 °C at t = 2000s, with the porosity increasing from 1% to 60%. The uniformity of the temperature distribution deteriorated as the porosity increases, and the temperature gradients between the center and edge of the samples with the porosity of 1% and 60%, were ∼80 °C and ∼130 °C at t = 2000s, respectively. [ABSTRACT FROM AUTHOR]

In this paper, an insulating film was successfully prepared by sintering 35 wt % CaO-15 wt % Al2O3-10 wt % B2O3-40 wt % SiO2 glass at 875 °C. After sintering, the main component of the insulating film was glass-ceramics. The main crystal phase was CaAl2Si2O8, and the crystallization activation energy was 189.76 kJ/mol. After preparing the insulating film, its color turned yellow, and the diffusion of Ag was found by XPS and XRD data. When the temperature increased to 875 °C, the color of the insulating film became lighter, and the silver content decreased. The adhesion of the multilayer structure could reach 875 N. The dielectric constant of the insulating film in the multilayer structure was approximately 5, and the dielectric loss was 0.0011. After sintering, the dielectric strength of the insulating film could reach 13.11 kV/mm, which fully meets the requirements of a complex packaging structure. [ABSTRACT FROM AUTHOR]

Abstract: Tb-doped SrSi2O2N2 phosphors with promising luminescent properties were synthesized by the conventional solid-state reaction method, characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. The synthesized materials exhibited a weak blue emission and a strong green emission in the region of 400–470nm and 480–650nm, which are attributed to 5D3→7F j (j=5, 4, 3) and 5D4→7Fj (j=6, 5, 4, 3) transitions of Tb3+, respectively. The green emission from 5D4→7F5 at 543nm showed the highest intensity under the optimized concentration of 0.1mol, after which the quenching concentration became relevant. The quenching behavior of the emission of Tb3+ was explained by the cross-relaxation of its excited state. [Copyright &y& Elsevier]

Abstract: The oxygen content is usually difficult to control in direct bonding copper process. In this study a new method for preparation of direct bonding copper on alumina ceramic substrates was realized. 96% Al2O3 ceramic substrates were first oxidized by pasting a thin layer of Cu2O and firing at 1150 °C in air. Then copper foil was bonded to the substrate by heating to 1070 °C in pure N2 atmosphere. Microstructure and composition of the interface between the copper and Al2O3 ceramic were analyzed. The XRD and EDS results show that an interphase of CuAlO2 was formed and a eutectic transformation between oxygen and copper took place at the interface of the copper and the ceramic substrate. The interface was much thicker than the traditionally bonded substrates, which resulted in a better bonding strength. The directly bonded copper alumina substrate samples showed no evidence of de-bonding after 50 thermal cycles comprising quenching from 220 °C to room temperature. [Copyright &y& Elsevier]

Phosphor layers are of vital importance for the development of advanced phosphor-converted light-emitting diodes (LEDs). However, owing to the fixed ratio of red-green-blue (RGB) phosphors, it has been difficult for the RGB phosphor layers with conventional structure to tune light emission colours. Herein, we have experimentally fabricated nine types of phosphor layers with patterned RGB pixel array, which consist of tuneable RGB ratio in a planar configuration. Moreover, we carried out optical simulation based on Monte-Carlo theory to assist in adjusting the light-emission colours and the corresponding chromaticity coordinates. The simulations were further verified by the experimental results via samples fabricated by the stencil printing technique. In accordance with the nine types of phosphor layers with patterned pixel arrays in various RGB ratios, we have finally obtained corresponding nine light-emission colours for the applications of LED light emission decoration. These designed advanced pixel-array phosphor layers demonstrate great potential for applications in decorated light emission and display devices with significant implications for industrial improvement in these research areas. • Nine patterned phosphor layers can realize nine output light colours. • With increasing mixing time of RGB phosphors, more output light colours of phosphor layers can be obtained. • The pixel-array phosphor layers was prepared via stencil printing method which is suitable for a large-scale production. [ABSTRACT FROM AUTHOR]

Herein, Ce3+ and Ce3+/Dy3+ co-doped Ca 3 Al 2 O 6 phosphors have been designed and synthesized via a facile citrate-based sol-gel technique, and their structural, photoluminescence properties and energy transfer phenomenon were investigated comprehensively. The XRD analysis indicated that pure Ca 3 Al 2 O 6 phase can be synthesized at low temperature (1000 °C) for merely 2 h. The photoluminescence spectra showed the dominant emission of Ce3+ singly doped phosphors is located in the blue region even at low Ce3+ doping level, which indeed favors the energy transfer from Ce3+ to other luminescent centers. When Dy3+ is co-doped into Ca 3 Al 2 O 6 :Ce3+ phosphors, the remarkable sensitizing effect of Ce3+ on Dy3+ is validated by comparatively analyzing the excitation, emission spectra and average lifetimes of the series of samples. Through the concentration quenching theory, the critical distance between Ce3+ and Dy3+ is calculated to be 13.50 Å. Furthermore, the energy transfer mechanism between them is most likely ascribed to electric dipole-dipole interaction. In virtue of the variation of the emission intensities of Ce3+ and Dy3+, the emitting colors of Ca 3 Al 2 O 6 :Ce3+, Dy3+ phosphors can realize tunable luminescence from deep blue to bluish-white region through controlling the Dy3+ content. Based on these analysis, Ca 3 Al 2 O 6 :Ce3+, Dy3+ phosphors could potentially be applied as a single-phase color-tunable phosphors pumped by near-ultraviolet (n-UV) radiation. • Developed a facile sol-gel method to prepare successfully Ca 3 Al 2 O 6 compound. • The blue emission of as-prepared Ca 3 Al 2 O 6 :Ce3+ phosphors dominates, which favors the energy transfer process. • The possible mechanism for the dominance of blue emission was discussed. • The energy transfer phenomenon in Ca 3 Al 2 O 6 :Ce3+, Dy3+ phosphors was investigated in detailed. • Ca 3 Al 2 O 6 :Ce3+, Dy3+ can serve as a single-phase color-tunable phosphors excited by near-ultraviolet radiation. [ABSTRACT FROM AUTHOR]

Rod-like single-phase crystals of Y-α-SiAlON were synthesized by combustion of Si, Al, α-Si3N4, SiO2 and Y2O3 powders. SEM observation of crystals, separated by chemical etching (HNO3/HF=2:1) followed by ultrasonic agitation in ethanol showed rod-like crystals, assigned to almost pure and well crystallized α-SiAlON. [Copyright &y& Elsevier]

BaO-Sm 2 O 3 –5TiO 2 (BST) added by Al 2 O 3 was prepared by solid-state reaction method. The main phase is Ba 3.99 Sm 9.34 Ti 18 O 54 of orthorhombic tungsten bronze structure, and the secondary phase is Ba 1.18 Al 1.90 Ti 6.09 O 16 of tetragonal structure, which has two types of grains: one is grey and cubic, and the other is white and quasi-rectangular. Microstructure was characterized by XRD, SEM, and Raman spectra. Micromechanical properties of different phases were assessed by nanoindentation and micro-scratch tests with Berkovich indenter. Volume fractions of different phases obtained by statistical analysis of grid indentation are in good agreement with those obtained by XRD analysis. Vickers hardness method is more appropriate for the determination of the fracture toughness of dielectric ceramics. BST ceramic without addition of Al 2 O 3 has better mechanical properties than BST-A with addition of Al 2 O 3 , indicating that addition of Al 2 O 3 impairs the micromechanical properties of dielectric ceramics. [ABSTRACT FROM AUTHOR]

Bio-based vitrimers present a promising solution to the issues associated with non-renewable and non-recyclable attributes of traditional thermosetting resins, showcasing extensive potential for diverse applications. However, their broader adoption has been hindered by the requirement for catalyst inclusion during the synthesis process. In this study, a cardanol-based curing agent with poly-hydroxy and tertiary amine structures was prepared by a clean synthetic method under the theory of click chemistry. The reaction of a cardanol-based curing agent with diglycidyl ether of bisphenol A formed catalyst-free, self-healing, and recyclable bio-based vitrimers. The poly-hydroxy and tertiary amine structures in the vitrimers promoted the curing of epoxy-carboxylic acid in the cross-linked network and served as internal catalysts of dynamic transesterification. In the absence of catalysts, the vitrimers network can achieve topological network rearrangement through dynamic transesterification, exhibiting excellent reprocessing performance. Moreover, the vitrimers exhibited faster stress relaxation (1500 s at 180 °C), lower activation energy (92.29 kJ·mol−1) and the tensile strength of the recycled material reached almost 100% of the original sample. This work offers a new method for preparing cardanol-based epoxy vitrimers that be used to make coatings, hydrogels, biomaterials, adhesives, and commodity plastics in the future. [ABSTRACT FROM AUTHOR]

The high integration density of microelectronic devices leads to local heat accumulation, and effective heat dissipation and signal transmission of packaging materials have become the primary issues to be solved. However, existing polymer materials have difficulty meeting the requirements due to their unsatisfactory thermal conductivity and thermal expansion properties. In this work, we proposed the use of digital light processing (DLP) printing technology to construct a triply periodic minimum surface (TPMS) skeleton, and a continuous and efficient heat conduction path was successfully constructed in epoxy resin by impregnating h-BN on the skeleton surface. When the loading of h-BN was 20 vol%, the thermal conductivity of the TPMS(SiO 2)@BN/EP(BN) composites was 1.86 W/(m·K), which was 786 % higher than that of pure epoxy resin. In addition, the thermal expansion coefficient of the composites decreased by more than 70 %. At the test frequencies of 3∼10 MHz, the composites showed stable dielectric properties, and the dielectric constant was always maintained in a low range, between 3.85 and 4.15. This work has realized the transformation of the method for constructing a heat conduction path from disordered to ordered and from random to repeatable. This provides a new strategy for the selection of microelectronic packaging materials. [ABSTRACT FROM AUTHOR]

We developed a newly-designed TiN/AgCuTi composite brazing alloy to significantly improve the bonding strength of AlN/Cu composite ceramics, which can endow high power electronic devices with superior compatibility with large current transport and high voltage resistance. Via the systematic microstructure investigation of the brazed joint by scanning electron microscopy and X-ray diffractometer, we found that added TiN particles could decrease the thickness of brittle reaction layer and promote the formation of fine TiCu particles in brazed joint, leading to dispersion strengthened and decreased CTE mismatch of the ceramic/metal composite. Importantly, the maximum bonding strength of 131 MPa was obtained for AlN and copper foil brazed joining via composite filler with TiN(4 wt.%)/AgCuTi, which is approximately 150 % higher than the case without TiN addition. [ABSTRACT FROM AUTHOR]

This paper presents that polyethylene glycol (PEG) synthesizes a form-stable phase change material (FS-PCM) with high thermal conductivity and considerable heat storage density. PEG was confined to the chain structure of epoxy resin (EP) via high-temperature melt blending and curing, which solves the leakage problem of PCMs during phase transformation. In order to increase the thermal conductivity and stability of the PEG/EP while maintaining good heat storage capacity and insulation ability, a low loading of reticulated porous Al 2 O 3 ceramic (RPC) was introduced into the PEG/EP matrix. RPC increases the thermal conductivity of FS-PCM by 5.5 times and the heat storage rate by 4 times. In addition, FS-PCM filled with 13.8 vol% RPCs has a coefficient of thermal expansion (CTE) of 80 ppm/K at 85–150 °C -a decrease of 62% over the matrix. Furthermore, the BN network is formed on RPC by vacuum impregnation technology, which further improves the thermal conductivity. This novel FS-PCM has excellent comprehensive properties and does not need for case package, indicating great prospects in thermal management and thermal storage. [ABSTRACT FROM AUTHOR]

In this study, hydrogen was determined in the ER5183 wires for MIG welding, and the effect of hydrogen in the wires on the tensile strength as well as the fracture behavior of Al–Mg MIG weld were investigated in order to clarify the affecting mechanism by hydrogen, which provided a reasonable range of hydrogen content in ER5183 welding wires. The results showed that, with the increasing hydrogen content, the tensile strength of the corresponding welds decreased accordingly. During the fracture process of the weld, hydrogen played serious roles as follows, accelerating the fracture process, promoting the formation of pores and causing the decohesion of the inclusion and matrix. By the mechanisms mentioned above, hydrogen changed the feature of fracture morphology from dimples to various defects. Considering the high tensile strength as well as the fine microstructure of the welds, the hydrogen content of the ER5183 welding wires should be controlled below 0.18 μg/g. • Determining the hydrogen content in the ER5183 welding wires for MIG welding. • Investigating the effect of hydrogen content on the tensile strength as well as the fracture behavior of Al–Mg MIG weld. • Finding the decohesion phenomenon, crack and porosity in the weld microstructure. • Giving a reasonable range of hydrogen content in ER5183 aluminum welding wire. [ABSTRACT FROM AUTHOR]

Phosphor layer are essential in the application of phosphor-converted white light emitting diodes (pc-WLEDs). However, the conventional structure of red–green–blue (RGB) phosphor layers can cause severe re-absorption of blue light, resulting in low luminous efficiency and colour rendering index (CRI). In this paper, we fabricated a new WLEDs phosphor layer, which consisted of patterned RGB phosphor pixel arrays in a planar configuration, by the stencil printing technique. Optical simulation based on Monte-Carlo theory has been applied to assist designing the optimal pattern of the phosphor pixel arrays. By tuning the layout of the pixel arrays and the size of phosphor pixels, we achieved uniform output white light with high luminous intensity of 1.47 × 109 cd and CRI of 95.6, which are superior compared with the intensity of 1.11 × 109 cd and CRI of 93.5 obtained from WLEDs with conventional dispensing phosphor layer. Our newly-designed phosphor pixel-array layer possesses great potential for applications in advanced lighting and display devices with vast implications for industrial improvement in these research areas. [ABSTRACT FROM AUTHOR]

This work focused on the influence of hydrogen content on the microstructure and mechanical properties of ER5183 Al-Mg-Mn alloy wires for aluminum alloy welding. The hydrogen content of the ER5183 wires was measured, the macroscopic and microscopic morphologies of fractures were observed as well as the microstructure of the wires, and the tensile strength of the wires was also tested and investigated. The experimental results demonstrated three typical irregular macroscopic fractures of the wires appeared during the drawing process when the hydrogen content exceeded 0.23 μg/g. In the meantime, the aggregated pores were observed in the microstructure of the ϕ5.2 mm wire with the hydrogen content of 0.38 μg/g. Such defects may become the origin of cracks in subsequent processing and tensile tests. Moreover, higher hydrogen content in the ϕ5.2 mm welding wire will bring obvious changes in the fracture surface, which are internal cracks and micropores replacing the original uniform and compact dimples. With the higher hydrogen content, the tensile strength and plastic strain rate of ϕ1.2 mm wires would decrease. At the same time, unstable crack propagation would occur during the process of plastic deformation, leading to fracture. Considering the mechanical properties and microstructure, the hydrogen content of the ER5183 wires should be controlled below 0.23 μg/g. [ABSTRACT FROM AUTHOR]

Recently, there has been strong interest in inorganic solid-state electrolytes for all-solid-state batteries, among which the garnet electrolyte LLZO has attracted much attention due to its excellent properties, such as high ionic conductivity and broad electrochemical stability. The aim of our study was to improve the performance of Ta-doped LLZO (LLZTO) by co-doping Ga and Y at the Li and La sites using conventional solid-phase synthesis methods. We thoroughly investigated how Ga and Y affect the microstructure and electrochemical properties of LLZTO. The results show that the relative density of Ga- and Y-doped LLZTO increases significantly up to 94% under the same sintering conditions. This doping resulted in a significant increase in ionic conductivity from 2.0 × 10−4 S·cm−1 to 1.05 × 10−3 S·cm−1 and a decrease in electronic conductivity from 2.16 × 10−7 S·cm−1 to 9.18 × 10−8 S·cm−1. Subsequently, the symmetric cells were assembled and tested, and it was found that the interfaces of the doped solid-state electrolytes were much more stable and that the cycling time was longer. Thus, our study successfully coordinated the co-doping of Ga, Y, and Ta, providing valuable insights for the subsequent production of LLZO materials with higher densities and better performance. This study is a promising step toward the realization of safer all-solid-state batteries with higher energy densities. • Innovative further doping of two elements on top of LLZTO solid electrolyte, harmonizing the doping of three elements. • An order of magnitude increases in ionic conductivity of LLZTO solid state electrolytes after doping. • The doped LLZTO solid state electrolyte has better suitability with lithium metal anode. [ABSTRACT FROM AUTHOR]

Different microstructures were obtained under various thermal conditions by adjusting the heat treatment parameters of the Cr-Co-Ni-Mo series of ultra-high strength stainless steel. The effect of organizational evolution on the stress corrosion cracking (SCC) of the Cr-Co-Ni-Mo series of ultra-high strength stainless steel was investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and other test methods in combination with slow strain rate tensile tests (SSRTs). The results show that the Mo- and Cr-rich clusters and precipitation of the Laves phase reduce the corrosion resistance, while increasing the austenite content can improve the corrosion resistance. The Cr-Co-Ni-Mo series of ultra-high strength stainless steel has a high SCC resistance after quenching at 1080 °C and undergoing deep cooling (DC) treatment at −73 °C. With increasing holding time, the strength of the underaged and peak-aged specimens increases, but the passivation and SCC resistance decreases. At the overaged temperature, the specimen has good SCC resistance after a short holding time, which is attributed to its higher austenite content and lower dislocation density. As a stable hydrogen trap in steel, austenite effectively improves the SCC resistance of steel. However, under the coupled action of hydrogen and stress, martensitic transformation occurs due to the decrease in the lamination energy of austenite, and the weak martensitic interface becomes the preferred location for crack initiation and propagation. [ABSTRACT FROM AUTHOR]

A multicolour LED is a miniaturized, long-lasting, and easy-to-achieve colour adjustable emission light source. It is widely used in outdoor displays and room lighting fields. However, the increase in the cost and the decrease in luminous efficiency when adjusting lighting colours have constrained the development of multicolour LEDs. In this study, we initially designed a phosphor conversion pixel array through optical simulation and then prepared the phosphor conversion pixel arrays with different layouts using a semi-cured template method. Finally, we packaged the phosphor conversion pixel array with the blue LED array as a remote phosphor LED. The measurement of the luminous performance indicated that the colour gamut of multicolour LEDs was included in the simulated colour gamut, and the colour of the light was consistent with the design guidelines. Notably, the multicolour LED emission efficiency packaged with a phosphor conversion pixel array could reach 125 lm/W, and the hexagonal phosphor conversion pixel array had better emission performance than the square phosphor conversion pixel array. • Based on the Monte Carlo principle, multicolour LEDs composed of array phosphor-converted film and blue-LED chip are designed. • Phosphor-converted pixel arrays are prepared by semi-cured template method with high moulding quality. • By comparing the experimental and simulation results, colour-tuneable characteristics of the multicolour LEDs is verified. • The luminous efficiency of multicolour LEDs reach up to 125.0 lm/W and changing pixel can reduce the secondary reabsorption of fluorescence. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure and photoluminescence properties of Eu2+ doped Li2Ca0.7Sr0.3SiO4 phosphors were investigated. The Li2Ca0.7Sr0.3SiO4 is not an alloy between the tetragonal Li2CaSiO4 and hexagonal Li2SrSiO4 but crystallizes in orthorhombic structure similar to Li2(CaSr)SiO4. Photoluminescence properties of the Li2Ca0.7Sr0.3SiO4:Eu2+ phosphors, summarized in effective excitation in the UV region, strong emission in the blue light range (with a peak at 427nm) and the CIE chromaticity coordinate (0.154, 0.038), indicate this phosphor has great potential in UV-chip pumped white LEDs. White light output by mixing the Li2Ca0.7Sr0.3SiO4:Eu2+ blue and Li2SrSiO4:Eu2+ yellow phosphor was attempted. With proper molar ratio of these two compound phosphors, warm white light with CIE chromaticity coordinate close to that of the nature white light (0.33, 0.33) and color temperature about 5000K was obtained. The results indicated that the Li2Ca0.7Sr0.3SiO4:Eu2+ may become an important phosphor candidate for ultra-violet chip pumped and multi-phosphors converted white LEDs. [Copyright &y& Elsevier]