Multi-colour light emission based on pixel-array phosphor layer in LEDs

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

Novel blue-emitting KBaGdSi2O7:Eu2+ phosphor used for near-UV white-light LED

Novel blue-emitting KBaGdSi2O7:Eu2+ phosphors were designed and synthesized through solid-state reaction method. The structural properties, concentration, and temperature-dependent luminescence behaviors of these phosphors were investigated in detail in this paper. Studies revealed that KBaGdSi2O7:Eu2+ phosphors have an intense absorption in the broad wavelength ranging from 250 to 400 nm that is suitable for the commercial near-UV LED, and give out intense blue light peaked at 475 nm with a full-width half-maximum of 75 nm. The crystallographic information of KBaGdSi2O7 phase is revealed from XRD pattern by Rietveld refinement. Band gap is derived to be 3.93 eV through diffuse reflection spectra through Kubelka Munk function. The concentration quenching mechanism is identified as the dipole–dipole interaction. Moreover, the thermal quenching experiment was also conducted and the activation energy is calculated as 0.3069 eV, which indicates this novel KBaGdSi2O7:Eu2+ phosphor has good thermal stability. These properties exhibit its potential commercial application for near-UV white-light LEDs (w-LEDs)

The microstructure and dielectric properties of titanium oxide doped with nano CuO

The TiO2 ceramics doped with nano CuO were fabricated by the conventional solid-state reaction method. The crystal structure, microstructure, microwave dielectric properties and lattice vibrations of TiO2 ceramics doped with nano CuO have been investigated. Nano CuO with higher sintering capability worked as flux former and effectively improved the sintering process of TiO2 ceramics. The microwave dielectric properties of TiO2 doped with nano CuO were much better than that doped with micron CuO at the same doping content. Raman spectra showed that the full width at half maximum of Eg mode of TiO2 doped with micron CuO was larger than nano CuO doped ones, which indicated a poor crystalline and a short phonon lifetime. TiO2 doped with 1 wt.% nano CuO, sintered at 950°C for 2 h had compact and homogeneous microstructure and possessed the following dielectric properties: εr = 106, Q × f = 24808, τf = 371 ppm/°C

Effect of niobium alloying on the austenite grain growth and mechanical properties of ultrahigh-strength stainless steel

In the temperature range of 1000 °C–1150 °C and the holding time range of 30–150 min, the effect of niobium (Nb) on the behavior of grain growth and the evolution pattern of the mechanical properties of a martensitic stainless steel was studied. This study found that the addition of Nb allowed a large amount of undissolved NbC phase to be present in the steel, that the dragging effect of the solute atoms such as solute Nb and Mo reduced the migration rate of the grain boundary , and the pinning effect of NbC hindered the growth of grains, and that the growth rate of grains in 0.11Nb steel was slow in the temperature range of 1000 °C–1080 °C and increased significantly at the temperature range of 1080 °C–1150 °C. Next, the kinetic equations of the grain growth of 0.002Nb steel and 0.11Nb steel were constructed. The second phase strengthening of NbC and the fine grain strengthening jointly increased the yield strength of the steel but reduced the plasticity and ultimate tensile strength (UTS) of the steel. The addition of Nb had a minor effect on the content of retained austenite in the steel, but its refining effect on the hierarchical martensite microstructure increased the number of nucleation sites of retained austenite, reduced their sizes, made their distribution more dispersed, and more effectively hindered crack propagation, thus improving the toughness of the steel

Characterization of Glass Insulating Thick Films with Ag Conductors for Multilayer Packages

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

Hybrid silver pastes with synergistic effect of multi-scale silver fillers and the application in flexible circuits

Silver circuits prepared by new hybrid pastes exhibit high electrical conductivity and mechanical properties, which are ideal for modern flexible electronics. Herein, the hybrid silver pastes composed of different silver nanoparticle content (0, 10, 20, 30 wt%), micron-sized silver flakes and epoxy-based binders were prepared. The corresponding electrical conductivity and bending resistance of the screen-printed silver circuits were studied. The experimental results demonstrated that the synergistic effect of micro-size silver flakes and nanoparticles can greatly improve the electrical conductivity and bending resistance of flexible circuits. Specifically, the silver circuits with 46 wt% micro-size silver flakes and 20 wt% silver nanoparticles incorporation exhibit a lower electrical resistivity of 8.1 × 10 ^−5 Ω·cm. Moreover, 10 wt% silver nanoparticles can be applied to significantly reduce the resistance change of flexible circuit, indicting a superior bending property. Our designed hybrid silver pastes with excellent performance might enable valuable applications in advanced electronic devices

Characterization of Glass Insulating Thick Films with Ag Conductors for Multilayer Packages

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

Tunable luminescence and energy transfer from Ce3+ to Dy3+ in Ca3Al2O6 host matrix prepared via a facile sol-gel process

Herein, Ce3+ and Ce3+/Dy3+ co-doped Ca3Al2O6 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 Ca3Al2O6 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 Ca3Al2O6: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 Ca3Al2O6:Ce3+, Dy3+ phosphors can realize tunable luminescence from deep blue to bluish-white region through controlling the Dy3+ content. Based on these analysis, Ca3Al2O6:Ce3+, Dy3+ phosphors could potentially be applied as a single-phase color-tunable phosphors pumped by near-ultraviolet (n-UV) radiation

A preparation method for Al/AlN ceramics substrates by using a CuO interlayer

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 N2-H2 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 CuAlO2, 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 Al2Cu 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

Synthesis and luminescence enhancement of CaySr4-x-yAl2O7:xEu(2+) phosphors by a novel halide-assisted solid-state reaction method

Eu2+ doped strontium aluminate phosphors CaySr4−x−yAl2O7:xEu2+ (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1) were synthesized via a novel halide-assisted solid-state reaction method. The phase structure and photoluminescence properties of CaySr4−x−yAl2O7:xEu2+ were characterized via X-ray diffraction (XRD) and fluorescence spectrophotometer. The XRD patterns indicate that the α-Sr4Al2O7 phase structure with negligible impurities were produced in the samples of CaySr4−x−yAl2O7:xEu2+ (x ≤ 0.1 and y ≤ 0.1) at 1450 °C. Photoluminescence results show that the CaySr4−x−yAl2O7:xEu phosphor with NH4I as reductant presents typical intense Eu2+ red emission bands centered at 610 nm while excited by 450 nm. Accordingly, samples without NH4I only exhibit two weak Eu3+ emission peaks located at 598 and 619 nm, respectively. It can be ascribed to the reduction characteristic of I− ion. Furthermore, by partial replacement of Sr2+ with Ca2+ in Sr4Al2O7 host, the emission intensity is enhanced up to 260% with emission peak red shifted by 5–10 nm. These results indicate that partial substitution of Sr2+ by Ca2+ is an efficient way to increase the proportion of longer wavelength emission and luminescence intensity for Sr4Al2O7:Eu phosphors