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The cyan-emitting BaSi 2 O 2 N 2 :Eu2+ phosphor is a promising narrow-band and high-efficiency luminescent material used in wide-color-gamut white light-emitting diodes (wLEDs). However, its serious degradation under thermal attacks hinders its practical applications and needs to be improved. Herein, we proposed to deposit a nano-sized Al 2 O 3 film around each BaSi 2 O 2 N 2 :Eu2+ particle through atomic layer deposition (ALD) in a fluidized bed reactor to improve its thermal stability. Thermal gravimetric analysis results showed that the Al 2 O 3 layer with a thickness of only 11 nm had an obvious anti-oxidization effect, by which the oxidation temperature in air of the Al 2 O 3 coated phosphor was largely increased from ∼550 to ∼750 °C. Moreover, the Al 2 O 3 coated phosphor remained 93% of its luminescence intensity in comparison to 73% of the uncoated one when degraded under water-steam at 200 °C for 24 h. The oxidization of both the BaSi 2 O 2 N 2 host matrix and the doped Eu2+ ions was reduced by the Al 2 O 3 layer. Meanwhile, the wLEDs fabricated with the Al 2 O 3 coated phosphor showed a luminous flux of 3 times higher than that of the uncoated one when aged under 100 mA for 300 h. The greatly improved thermal degradation property of BaSi 2 O 2 N 2 :Eu2+ phosphor and the reliability of the wLEDs indicate that the ALD approach could be a feasible route to produce uniform and nano layers on phosphors and enhance their stability. [ABSTRACT FROM AUTHOR]

Single-component white phosphor is highly desirable to obtain efficient and stable white light-emitting diodes (w-LED). In this paper, a series of Bi3+, Tb3+, and Eu3+ doped Ca 3 LuAl 3 B 4 O 15 (CLAB) luminescent materials were successfully prepared. The structure, morphology, and optical properties of samples were characterized by X-ray diffractometer, scanning electronic microscopy, and fluorescence spectroscopy, respectively. The synthesized phosphor exhibits strong blue band emission from Bi3+ and intense characteristics line emission from Tb3+ and Eu3+ under ultraviolet (UV) light excitation. The emission color can fine be adjusted by changing the doping content of the three activators. The warm white light of CLAB:0.5%Bi3+,2%Tb3+,0.75%Eu3+ with CIE chromaticity coordinates of (0.3728,0.3166), a CCT of 3671 K, and a Ra index of 87 could be realized under UV light excitation. The fabricated w-LED by combining UV chip with CLAB:0.5%Bi3+,2%Tb3+,0.75%Eu3+ shows excellent thermal stability after high-temperature aging test, implying its promising application in single-phosphor-converted warm w-LEDs. A single-phosphor-converted warm w-LED fabricated by UV chip with CLAB:Bi3+,Tb3+,Eu3+ shows thermally robust properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Joining of Al 2 O 3 ceramic to Cu has been conducted with Ag-26.7Cu-4.5Ti braze and refractory metal (W or Ta) foil. The interfacial microstructure in the joint with W foil is similar to that with Ta foil. The joining region in the joint consists of a reaction zone, braze zone I, refractory metal layer and braze zone II. The reaction zone of Cu 3 Ti 3 O with a thickness of about 5 μm develops close to Al 2 O 3 side due to the reactions of Ti and Cu in the braze with Al 2 O 3 substrate. The braze zones I and II are mainly composed of Ag- and Cu-based solid solutions. For the joint with W foil, the adsorption of Ti at the braze/W interfaces followed by the Ti diffusion into W foil occurs, whilst slight dissolution and diffusion of Ta into the brazes take place in the joint with Ta foil. The average shear strengths of joints with W and Ta foils are much higher than those without refractory metal foil, indicating the contribution of the refractory metal foil to the improvement of joint mechanical strength. Introduction of refractory metal foil in Al 2 O 3 /Cu joining is beneficial for the shift of joint residual stress distribution and the decrease of stress concentration in the joint since the coefficient of thermal expansion (CTE) of refractory metal layer approximately approaches that of Al 2 O 3. Furthermore, a slight thickness increase of the Cu 3 Ti 3 O reaction zone in the joint with refractory metal foil may also give rise to the joint strength promotion. [ABSTRACT FROM AUTHOR]

Chemical stability of phosphors is critical to the efficiency and lifetime of the white light-emitting diodes. Therefore, many strategies have been adopted to improve the stability of phosphors. However, it is still lack of report on the improvement of thermal stability and hydrolysis resistance of phosphors by a single layer coating. Due to the high transmittance and high chemical inertness of graphene, it was coated on the surface of Sr 2 Si 5 N 8 :Eu2+ phosphor by chemical vapor deposition, aiming to improve its thermal stability and hydrolysis resistance. The chemical composition and microstructure of the coating were characterized and analyzed. A nanoscale carbon layer was attached on the surface of Sr 2 Si 5 N 8 :Eu2+ phosphor particles in an amorphous state. In coated Sr 2 Si 5 N 8 :Eu2+ phosphor, the oxidation degree of Eu2+ to Eu3+ was significantly suppressed. At the same time, the surface of Sr 2 Si 5 N 8 :Eu2+ particle turned from hydrophilic to hydrophobic after carbon coating, and consequently the hydrolysis resistance of Sr 2 Si 5 N 8 :Eu2+ phosphor was greatly improved. After tests at 85 °C and 85% humidity for 200 h, the carbon coated Sr 2 Si 5 N 8 :Eu2+ phosphor still maintained about 95% of its initial luminous intensity as compared with 35% of the uncoated. By observing the in-situ microstructure evolution of coated phosphor in air-water vapor environment, remained presence of the carbon layer even at 500 °C explained the excellent chemical stability of carbon coated Sr 2 Si 5 N 8 :Eu2+ phosphor in complex environment. These results indicate that a nanoscale carbon layer can be used to provide superior thermal stability and hydrolysis resistance of (oxy) nitrides phosphors. [ABSTRACT FROM AUTHOR]

Low infrared emissivity in 3–5 μm or 8–14 μm band has been realized in different host materials. Realizing the low infrared emissivity in single material covering the entire band is rarely achieved. This research explores a binary system of ultra-high temperature ceramic ZrB 2 –CeO 2 composites prepared by solid state sintering. their phase composition, microstructure evolution, reaction mechanism and infrared emissivity performance were discussed in detail. It was found that CeO 2 , ZrB 2 , ZrO 2 , and Zr n Ce 1-n O 2 existed in the sample in addition to the coated glass phase of CeO 2 on the surface of the sample. In-situ HRTEM results clearly revealed a series of reaction mechanism of CeO 2 and ZrB 2. With the increase of sintering temperature, the CeO 2 particles gradually transformed into a glass phase, and were distributed on the surface of ZrB 2 particles, and ZrO 2 was formed on the surface of ZrB 2 , simultaneously. Consequently, Zr n Ce 1-n O 2 is formed as the reaction of ZrO 2 and CeO 2. Compared with the infrared emissivity spectra of pure CeO 2 and ZrB 2 , a low infrared emissivity less than 0.2 in a wider coverage band of 3–5 and 8–14 μm in ZrB 2 –CeO 2 compounds was achieved as a result of synergistic interaction between CeO 2 and ZrB 2. The obtained information about the phase composition and microstructure evolution helps to realize low infrared emissivity in a wider coverage band in compounds via composition and microstructure modification. [ABSTRACT FROM AUTHOR]