The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Zhuhui Qiao - One of the best experts on this subject based on the ideXlab platform.
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the novel Sialon sn composite with high toughness and wear resistance prepared at a lower temperature
Tribology International, 2020Co-Authors: Qichun Sun, Jun Yang, Jun Cheng, Shengyu Zhu, Hui Tan, Zhuhui QiaoAbstract:Abstract In this study, SnO2 as a precursor of stannum was used to prepare a novel Sialon-Sn composite. The sintering behavior, fracture toughness and tribological properties were investigated. The results revealed that Sialon-Sn composite with high toughness and wear resistance can be prepared at a lower temperature. Using mixture with higher content of SnO2 makes it possible to perform the sintering under the temperature lower than in typical process. The fracture toughness can be improved by 19.6% compared with that of the composite without SnO2 at 25 °C. Moreover, the wear resistance can be enhanced by adding SnO2. Especially the wear rate of composite with 20% SnO2 is 20 times lower than the composite sintered without SnO2 at 800 °C.
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Sialon tailoring copper based composite to achieve high strength high strain integrated with excellent wear resistance
Tribology International, 2019Co-Authors: Qichun Sun, Zixi Wang, Jun Yang, Hui Tan, Zhuhui QiaoAbstract:Abstract In this study, Cu-Sialon composites were prepared, and their microstructure evolution, mechanical properties and tribological behaviors were thoroughly investigated. The experimental results show that the β-Sialon can play a significant role in grain refinement. Meanwhile, the composites can achieve the integration of high compressive strength, high strain and excellent wear resistance by doping Sialon. Especially for the CS3, the fracture strength and strain can reach 386 ± 12 MPa and 13.6 ± 2.2%, respectively. Meanwhile, its wear rate can be reduced by an order of magnitude. These are ascribed to the uniform distribution of Sialon particles, good interfacial bonding and grain refinement. Moreover, the wear mechanisms were also discussed.
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high performance tin reinforced Sialon matrix composites a good combination of excellent toughness and tribological properties at a wide temperature range
Ceramics International, 2018Co-Authors: Qichun Sun, Zixi Wang, Jun Yang, Jiongjie Liu, Yulin Liu, Zhuhui Qiao, Weimin LiuAbstract:Abstract TiN-doped Sialon matrix composites are potential candidates for high temperature applications due to their excellent mechanical and tribological properties. The objectives of this work are to thoroughly research the mechanical properties and tribological behaviors of the TiN reinforced Sialon composites and reveal their toughening and wear mechanisms. Results show that the fracture toughness can be obviously enhanced by doping TiN. The fracture toughness of the composite with 10 wt% TiN reaches the maximum value of 6.2 MPa m1/2 and 4.4 MPa m1/2 at 25 °C and 800 °C, respectively. Moreover, TiN reinforced Sialon composites exhibit excellent tribological properties at a wide temperature range. Especially for the composite with 30 wt% addition of TiN at 200–800 °C, the friction coefficient reduces to 0.46–0.60, and the wear rate decreases about 15–50 times as compared to the material without TiN. In addition, the toughening and wear mechanisms are revealed on the basis of the crack propagation behavior and tribological properties. The crack propagation behavior indicates that crack deflection is the principal toughening mechanism. The enhancement of heat-conducting property, mechanical properties, and the tribo-chemical reaction are the main friction-reducing and anti-wear mechanisms.
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the tribological properties and wear mechanism of copper coated graphite doped Sialon ceramic composites at wide range temperature from 25 to 800 c
Tribology International, 2018Co-Authors: Qichun Sun, Zixi Wang, Bing Yin, Jun Yang, Jiongjie Liu, Yulin Liu, Jun Cheng, Shengyu Zhu, Zhuhui QiaoAbstract:Abstract High-performance Sialon composites with excellent tribological properties were successfully fabricated by doped copper coated graphite. Results showed that Sialons have an excellent wear resistance (wear rate at 10−6 mm3/Nm) at 25 °C. When the temperature increases to 200–600 °C, the wear rate of β-Sialon composites decreases about 5–10 times compared to S0. Especially for S2 (the content of copper coated graphite is 30 wt%) at 600 °C, the wear rate decreases by an order of magnitude and the friction coefficient is reduced to 0.5, which is 37.5% lower than S0. The self-lubrication mechanism of Sialons ascribed to the synergistic effect of graphite and copper at wide range temperature.
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high toughness integrated with self lubricity of cu doped Sialon ceramics at elevated temperature
Journal of The European Ceramic Society, 2018Co-Authors: Qichun Sun, Bing Yin, Jun Yang, Jun Cheng, Shengyu Zhu, Zhuhui Qiao, Shuai Wang, Weimin LiuAbstract:Abstract High toughness integrated with self-lubricity of β-Sialon composites at elevated temperature containing second phase particles were successfully fabricated. It was found that the fracture toughness can be substantially improved by addition of Cu powder. The fracture toughness can be reached 6.75 MPa m1/2 and 4.42 MPa m1/2 at 25 and 900 °C, respectively. Meanwhile, the tribological properties of Cu-doped Sialons have a tremendous improvement at high temperature. Especially when the content of Cu powder is above 10 wt%, the wear rate decreases by two orders of magnitude and the friction coefficient reduces to 0.56–0.65 at 900 °C. In addition, the microstructure of composites was characterized, and crack propagation behavior and tribological behavior were discussed to clarify the toughening mechanisms and self-lubrication mechanisms. The results show that the principal toughening mechanisms are crack deflection and crack bridging. The tribo-chemical reaction and generated CuO films with lubricity are the main self-lubrication mechanisms.
Qichun Sun - One of the best experts on this subject based on the ideXlab platform.
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the novel Sialon sn composite with high toughness and wear resistance prepared at a lower temperature
Tribology International, 2020Co-Authors: Qichun Sun, Jun Yang, Jun Cheng, Shengyu Zhu, Hui Tan, Zhuhui QiaoAbstract:Abstract In this study, SnO2 as a precursor of stannum was used to prepare a novel Sialon-Sn composite. The sintering behavior, fracture toughness and tribological properties were investigated. The results revealed that Sialon-Sn composite with high toughness and wear resistance can be prepared at a lower temperature. Using mixture with higher content of SnO2 makes it possible to perform the sintering under the temperature lower than in typical process. The fracture toughness can be improved by 19.6% compared with that of the composite without SnO2 at 25 °C. Moreover, the wear resistance can be enhanced by adding SnO2. Especially the wear rate of composite with 20% SnO2 is 20 times lower than the composite sintered without SnO2 at 800 °C.
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Sialon tailoring copper based composite to achieve high strength high strain integrated with excellent wear resistance
Tribology International, 2019Co-Authors: Qichun Sun, Zixi Wang, Jun Yang, Hui Tan, Zhuhui QiaoAbstract:Abstract In this study, Cu-Sialon composites were prepared, and their microstructure evolution, mechanical properties and tribological behaviors were thoroughly investigated. The experimental results show that the β-Sialon can play a significant role in grain refinement. Meanwhile, the composites can achieve the integration of high compressive strength, high strain and excellent wear resistance by doping Sialon. Especially for the CS3, the fracture strength and strain can reach 386 ± 12 MPa and 13.6 ± 2.2%, respectively. Meanwhile, its wear rate can be reduced by an order of magnitude. These are ascribed to the uniform distribution of Sialon particles, good interfacial bonding and grain refinement. Moreover, the wear mechanisms were also discussed.
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high performance tin reinforced Sialon matrix composites a good combination of excellent toughness and tribological properties at a wide temperature range
Ceramics International, 2018Co-Authors: Qichun Sun, Zixi Wang, Jun Yang, Jiongjie Liu, Yulin Liu, Zhuhui Qiao, Weimin LiuAbstract:Abstract TiN-doped Sialon matrix composites are potential candidates for high temperature applications due to their excellent mechanical and tribological properties. The objectives of this work are to thoroughly research the mechanical properties and tribological behaviors of the TiN reinforced Sialon composites and reveal their toughening and wear mechanisms. Results show that the fracture toughness can be obviously enhanced by doping TiN. The fracture toughness of the composite with 10 wt% TiN reaches the maximum value of 6.2 MPa m1/2 and 4.4 MPa m1/2 at 25 °C and 800 °C, respectively. Moreover, TiN reinforced Sialon composites exhibit excellent tribological properties at a wide temperature range. Especially for the composite with 30 wt% addition of TiN at 200–800 °C, the friction coefficient reduces to 0.46–0.60, and the wear rate decreases about 15–50 times as compared to the material without TiN. In addition, the toughening and wear mechanisms are revealed on the basis of the crack propagation behavior and tribological properties. The crack propagation behavior indicates that crack deflection is the principal toughening mechanism. The enhancement of heat-conducting property, mechanical properties, and the tribo-chemical reaction are the main friction-reducing and anti-wear mechanisms.
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the tribological properties and wear mechanism of copper coated graphite doped Sialon ceramic composites at wide range temperature from 25 to 800 c
Tribology International, 2018Co-Authors: Qichun Sun, Zixi Wang, Bing Yin, Jun Yang, Jiongjie Liu, Yulin Liu, Jun Cheng, Shengyu Zhu, Zhuhui QiaoAbstract:Abstract High-performance Sialon composites with excellent tribological properties were successfully fabricated by doped copper coated graphite. Results showed that Sialons have an excellent wear resistance (wear rate at 10−6 mm3/Nm) at 25 °C. When the temperature increases to 200–600 °C, the wear rate of β-Sialon composites decreases about 5–10 times compared to S0. Especially for S2 (the content of copper coated graphite is 30 wt%) at 600 °C, the wear rate decreases by an order of magnitude and the friction coefficient is reduced to 0.5, which is 37.5% lower than S0. The self-lubrication mechanism of Sialons ascribed to the synergistic effect of graphite and copper at wide range temperature.
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high toughness integrated with self lubricity of cu doped Sialon ceramics at elevated temperature
Journal of The European Ceramic Society, 2018Co-Authors: Qichun Sun, Bing Yin, Jun Yang, Jun Cheng, Shengyu Zhu, Zhuhui Qiao, Shuai Wang, Weimin LiuAbstract:Abstract High toughness integrated with self-lubricity of β-Sialon composites at elevated temperature containing second phase particles were successfully fabricated. It was found that the fracture toughness can be substantially improved by addition of Cu powder. The fracture toughness can be reached 6.75 MPa m1/2 and 4.42 MPa m1/2 at 25 and 900 °C, respectively. Meanwhile, the tribological properties of Cu-doped Sialons have a tremendous improvement at high temperature. Especially when the content of Cu powder is above 10 wt%, the wear rate decreases by two orders of magnitude and the friction coefficient reduces to 0.56–0.65 at 900 °C. In addition, the microstructure of composites was characterized, and crack propagation behavior and tribological behavior were discussed to clarify the toughening mechanisms and self-lubrication mechanisms. The results show that the principal toughening mechanisms are crack deflection and crack bridging. The tribo-chemical reaction and generated CuO films with lubricity are the main self-lubrication mechanisms.
Weimin Liu - One of the best experts on this subject based on the ideXlab platform.
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high performance tin reinforced Sialon matrix composites a good combination of excellent toughness and tribological properties at a wide temperature range
Ceramics International, 2018Co-Authors: Qichun Sun, Zixi Wang, Jun Yang, Jiongjie Liu, Yulin Liu, Zhuhui Qiao, Weimin LiuAbstract:Abstract TiN-doped Sialon matrix composites are potential candidates for high temperature applications due to their excellent mechanical and tribological properties. The objectives of this work are to thoroughly research the mechanical properties and tribological behaviors of the TiN reinforced Sialon composites and reveal their toughening and wear mechanisms. Results show that the fracture toughness can be obviously enhanced by doping TiN. The fracture toughness of the composite with 10 wt% TiN reaches the maximum value of 6.2 MPa m1/2 and 4.4 MPa m1/2 at 25 °C and 800 °C, respectively. Moreover, TiN reinforced Sialon composites exhibit excellent tribological properties at a wide temperature range. Especially for the composite with 30 wt% addition of TiN at 200–800 °C, the friction coefficient reduces to 0.46–0.60, and the wear rate decreases about 15–50 times as compared to the material without TiN. In addition, the toughening and wear mechanisms are revealed on the basis of the crack propagation behavior and tribological properties. The crack propagation behavior indicates that crack deflection is the principal toughening mechanism. The enhancement of heat-conducting property, mechanical properties, and the tribo-chemical reaction are the main friction-reducing and anti-wear mechanisms.
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high toughness integrated with self lubricity of cu doped Sialon ceramics at elevated temperature
Journal of The European Ceramic Society, 2018Co-Authors: Qichun Sun, Bing Yin, Jun Yang, Jun Cheng, Shengyu Zhu, Zhuhui Qiao, Shuai Wang, Weimin LiuAbstract:Abstract High toughness integrated with self-lubricity of β-Sialon composites at elevated temperature containing second phase particles were successfully fabricated. It was found that the fracture toughness can be substantially improved by addition of Cu powder. The fracture toughness can be reached 6.75 MPa m1/2 and 4.42 MPa m1/2 at 25 and 900 °C, respectively. Meanwhile, the tribological properties of Cu-doped Sialons have a tremendous improvement at high temperature. Especially when the content of Cu powder is above 10 wt%, the wear rate decreases by two orders of magnitude and the friction coefficient reduces to 0.56–0.65 at 900 °C. In addition, the microstructure of composites was characterized, and crack propagation behavior and tribological behavior were discussed to clarify the toughening mechanisms and self-lubrication mechanisms. The results show that the principal toughening mechanisms are crack deflection and crack bridging. The tribo-chemical reaction and generated CuO films with lubricity are the main self-lubrication mechanisms.
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dry sliding wear behavior of β Sialon ceramics at wide range temperature from 25 to 800 c
Journal of The European Ceramic Society, 2017Co-Authors: Qichun Sun, Bing Yin, Jun Yang, Jiongjie Liu, Yulin Liu, Jun Cheng, Zhuhui Qiao, Hui Tan, Weimin LiuAbstract:Abstract The β-Sialons are potential candidates for high temperature application because of their excellent comprehensive performances. However, there is little research about dry sliding wear behavior of β-Sialons at wide range temperature. This study aims at revealing the mechanisms of how temperature, microstructure and mechanical properties affect the tribological properties of such composites. Four kinds of β-Sialons are prepared and their wear properties are characterized from 25 to 800 °C. Results show that β-Sialons have a preferable tribological property at 25 °C, which is ascribed to its excellent mechanical properties. Whereas, with temperature increasing, the wear rate increases two orders of magnitudes compared to 25 °C, owing to the reduced hardness and increased thermal stress of the sample. At 800 °C, the wear rate of composites decreases with z values increasing, which is attributed to the tribo-chemical reaction and generate more Al 2 O 3 in β-Sialons with higher z values during sliding process.
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friction and wear behaviors of a ca mg Sialon sae 52100 steel pair under the lubrication of various polyols as water based lubricating additives
Tribology International, 2000Co-Authors: Wenguang Zhang, Weimin LiuAbstract:The friction and wear behaviors of (Ca, Mg)-Sialon/SAE 52100 steel pair under the lubrication of water or various polyol aqueous solutions were investigated with an SRV friction and wear tester in a ball-on-disc configuration. This was conducted to simulate the effect of polyols as aqueous additive in machining Sialon ceramic. The morphologies of and elemental distributions in the worn surfaces of the lubricated Sialon ceramics and counterpart steel were observed and determined with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). All solutions of the tested polyols decreased the friction coefficient of (Ca, Mg)-Sialon/SAE 52100 steel effectively and increased the wear volume loss of (Ca, Mg)-Sialon to some extent as compared with dry sliding. The friction coefficients under the lubrication of distilled water and various polyols aqueous solutions of polyols showed almost no difference, and propanetriol was found to be the most effective for machining (Ca, Mg)-Sialon with the concentration of polyols in water fixed as 5 wt%. The friction coefficients under the lubrication of propanetriol aqueous solutions in varied concentrations are closely related with the concentration, which came to the lowest value of 0.04 at a concentration of 75%. The friction-reducing performance of the polyols as additives in water was roughly correlated with their wetting behaviors on the Sialon ceramic surface. In other words, the higher the wetting ability is, the lower the friction coefficients will be. Moreover, the wear volume losses of (Ca, Mg)-Sialon also varied with the variation in the concentration of propanetriol in water. Accounting for the friction-reduction and wear behavior, 20% concentration of propanetriol in water could be recommended for machining (Ca, Mg)-Sialon. Electron microscopic analysis indicates that polyols as additives in water enhanced the corrosive wear of Sialon ceramic, which could be beneficial for increasing the machining efficiency. There existed interactions among water, polyols and Sialon surfaces, which were dependent on the compositions of the lubricant solution. This accounts for the variations in the friction and wear behaviors with the concentration of polyols in water.
Rongjun Xie - One of the best experts on this subject based on the ideXlab platform.
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novel luminescent properties and thermal stability of non rare earth ca α Sialon mn2 phosphor
Journal of Luminescence, 2018Co-Authors: Qian Liu, Jieqiong Wan, Guanghui Liu, Zhenzhen Zhou, Xionghui Zeng, Rongjun XieAbstract:Abstract Recently, transition metal Mn 2+ ions emerged as a potent competitor of generally used rare-earth elements due to its abundant reserve and cheaper cost. In this work, the transition metal Mn 2+ doped Ca-α-Sialon phosphor with compositions of Ca 1-x Si 9 Al 3 ON 15 :xMn 2+ was designed and successfully prepared by high-temperature solid-state method. The produced Mn 2+ doped Ca-α-Sialon phosphor exhibits a dominant orange-red emission centered at ∼600 nm upon UV light excitation of 265 nm, which is ascribed to the characteristic 4 T1( 4 G)– 6 A1( 6 S) transition of Mn 2+ . The band gap energy (5.61 eV) of the phosphors was calculated based on UV–vis diffuse reflectance spectra. Spectroscopy of temperature-dependent emission demonstrates that the luminescence of the optimized Ca-α-Sialon:0.12Mn 2+ composition exhibits a good color stability against heat and excellent resistance to thermal impact, due to its high activation energy of 0.284 eV. Further, the Electron Paramagnetic Resonance (EPR) spectra were recorded to elucidate the structural characteristic of Mn 2+ and possible vacancy defects in phosphors. The internal quantum efficiency of the prepared product reaches up to ∼48.2%. All the results inform that this kind of phosphors may become a promising candidate as orange-red phosphor for W-LED application.
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optical properties of solid state laser lighting devices using Sialon phosphor glass composite films as wavelength converters
Japanese Journal of Applied Physics, 2016Co-Authors: Kenichi Yoshimura, Rongjun Xie, Kazunori Annen, Hiroshi Fukunaga, Masamichi Harada, Makoto Izumi, Kohsei Takahashi, Tetsuo Uchikoshi, Naoto HirosakiAbstract:In this work, Sialon phosphor–glass films were investigated as wavelength converters in solid-state laser lighting. The phosphor–glass composite films were prepared by dispersing phosphor powders into a silica precursor solution and sintering at 500 °C. Both simulation and experiment were carried out to evaluate the optical properties of solid-state lighting devices using Sialon:Eu or YAG:Ce–glass films. The device using Sialon:Eu phosphors initially has lower brightness than that of the device using YAG:Ce at lower laser powers, but the latter has an illuminance saturation at 1000 lx whereas the Sialon-based device is free of saturation even at higher laser powers. The device using Sialon phosphor–glass composite films has a maximum illuminance 15% higher than that of the device using YAG when the temperature exceeds 250 °C. These better optical properties are ascribed to the higher thermal stability of Sialon phosphors that are able to achieve high luminance and thermally robust solid-state lighting.
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synthesis crystal structure and photoluminescence of eu α Sialon
Journal of Alloys and Compounds, 2010Co-Authors: Kousuke Shioi, Rongjun Xie, Naoto Hirosaki, Takashi TakedaAbstract:Abstract Eu-α-Sialon (Eu m /2 Si 12− m − n Al m + n O n N 16− n ) was synthesized with nominal compositions having small m and n values, by firing the powder mixture of Eu 2 Si 5 N 8 , α-Si 3 N 4 , AlN, and Al 2 O 3 at 1900 °C for 6 h under 1 MPa nitrogen atmosphere. The ratio of the oxidation state of Eu 2+ /Eu 3+ was estimated from the X-ray absorption fine structure (XAFS) measurement. The observed X-ray absorption near edge spectrum (XANES) showed that the Eu ion in Eu-α-Sialon was mainly in divalent state but also coexisted with a small amount of Eu in the trivalent state. The crystal structure of Eu-α-Sialon was refined by the Rietveld analysis of the X-ray powder diffraction patterns. The lattice constants of the samples increased with increasing m and n values. The excitation band of Eu-α-Sialon ranged from the ultraviolet to the visible light region and a broad emission band centered at about 590 nm were observed. The emission intensity decreased significantly with increasing the ratio of trivalent Eu ion, suggesting that the trivalent Eu could be one of the luminescent killer centers.
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synthesis and photoluminescence properties of beta Sialon eu2 si6 zalzozn8 z eu2
Journal of The Electrochemical Society, 2007Co-Authors: Promising A Green, Rongjun Xie, N Hirosaki, M MitomoAbstract:Divalent europium-activated p-Sialon (Si 6-z Al z O z N 8-z , 0.1 ≤ S≤ S 2.0) phosphors with dopant concentration varying in the range of 0.02-1.5 mol % were synthesized by firing the powder mixture of α-Si 3 N 4 , AIN, Al 2 O 3 , and Eu 2 O 3 at 2000°C for 2 h under a nitrogen-gas pressure of 1.0 MPa. The phase purity, microstructure, luminescence spectra, and thermal quenching of the fired β-Sialon:Eu 2+ phosphors were investigated. The samples with lower z values (z≤ 1.0) showed higher phase purity, finer and more uniform particle size, and higher emission. Green luminescence of Eu 2+ (λ em = 528-550 nm) was achieved in p-Sialons upon near-ultraviolet (NUV) or blue-light excitations. Furthermore, the β-Sialon:Eu 2+ phosphors had small thermal quenching, the emission intensity of which attained 84-87% of that measured at room temperature. The experimental data clearly indicates that β-Sialon:Eu 2+ has great potentials as a down-conversion green phosphor for white light-emitting diodes (LEDs) utilizing NUV or blue LEDs as the primary light source.
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wavelength tunable and thermally stable li α Sialon eu2 oxynitride phosphors for white light emitting diodes
Applied Physics Letters, 2006Co-Authors: Rongjun Xie, Mamoru Mitomo, Naoto Hirosaki, Ken Sakuma, Naoki KimuraAbstract:Eu2+-activated Li-α-Sialon is a promising yellow phosphor for white light-emitting diodes (LEDs). This letter reports that the emission of Eu2+ in Li-α-Sialon can be tuned widely (563–586nm) by tailoring the composition or controlling the Eu2+ concentration. The thermal stability of Li-α-Sialon:Eu2+, relying a little on the composition and the Eu2+ concentration, remains high in a wide temperature range (25–200°C). Moreover, the chromaticity of Li-α-Sialon:Eu2+ does not shift with changes in temperature. Using a single Li-α-Sialon:Eu2+ phosphor, highly efficient white LEDs (46–55lm∕W) with different color temperatures (3000–5200K) can be fabricated.
Naoto Hirosaki - One of the best experts on this subject based on the ideXlab platform.
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optical properties of solid state laser lighting devices using Sialon phosphor glass composite films as wavelength converters
Japanese Journal of Applied Physics, 2016Co-Authors: Kenichi Yoshimura, Rongjun Xie, Kazunori Annen, Hiroshi Fukunaga, Masamichi Harada, Makoto Izumi, Kohsei Takahashi, Tetsuo Uchikoshi, Naoto HirosakiAbstract:In this work, Sialon phosphor–glass films were investigated as wavelength converters in solid-state laser lighting. The phosphor–glass composite films were prepared by dispersing phosphor powders into a silica precursor solution and sintering at 500 °C. Both simulation and experiment were carried out to evaluate the optical properties of solid-state lighting devices using Sialon:Eu or YAG:Ce–glass films. The device using Sialon:Eu phosphors initially has lower brightness than that of the device using YAG:Ce at lower laser powers, but the latter has an illuminance saturation at 1000 lx whereas the Sialon-based device is free of saturation even at higher laser powers. The device using Sialon phosphor–glass composite films has a maximum illuminance 15% higher than that of the device using YAG when the temperature exceeds 250 °C. These better optical properties are ascribed to the higher thermal stability of Sialon phosphors that are able to achieve high luminance and thermally robust solid-state lighting.
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properties of Sialon powder phosphors for white leds
Journal of The European Ceramic Society, 2012Co-Authors: Suzuya Yamada, Hideyuki Emoto, Masahiro Ibukiyama, Naoto HirosakiAbstract:Abstract Three kinds of Eu 2+ -doped oxynitride powder phosphors, including green β-Sialon, yellow Ca-α-Sialon and newly developed orange Ca-α-Sialon were prepared by gas pressure sintering, which emit the fluorescent light with emission peak at 540 nm, 585 nm and 597 nm, respectively. Emission intensity more than 90% can be kept in the range of temperature from 30 °C to 200 °C. Emission characteristics are stable after long-term exposure testing for 6000 h at temperature of 85 °C and in humidity of 85%. A white LED device composed of a blue LED chip, β-Sialon and orange Ca-α-Sialon phosphors exhibits a modest colour rendering index of 72.
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synthesis crystal structure and photoluminescence of eu α Sialon
Journal of Alloys and Compounds, 2010Co-Authors: Kousuke Shioi, Rongjun Xie, Naoto Hirosaki, Takashi TakedaAbstract:Abstract Eu-α-Sialon (Eu m /2 Si 12− m − n Al m + n O n N 16− n ) was synthesized with nominal compositions having small m and n values, by firing the powder mixture of Eu 2 Si 5 N 8 , α-Si 3 N 4 , AlN, and Al 2 O 3 at 1900 °C for 6 h under 1 MPa nitrogen atmosphere. The ratio of the oxidation state of Eu 2+ /Eu 3+ was estimated from the X-ray absorption fine structure (XAFS) measurement. The observed X-ray absorption near edge spectrum (XANES) showed that the Eu ion in Eu-α-Sialon was mainly in divalent state but also coexisted with a small amount of Eu in the trivalent state. The crystal structure of Eu-α-Sialon was refined by the Rietveld analysis of the X-ray powder diffraction patterns. The lattice constants of the samples increased with increasing m and n values. The excitation band of Eu-α-Sialon ranged from the ultraviolet to the visible light region and a broad emission band centered at about 590 nm were observed. The emission intensity decreased significantly with increasing the ratio of trivalent Eu ion, suggesting that the trivalent Eu could be one of the luminescent killer centers.
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wavelength tunable and thermally stable li α Sialon eu2 oxynitride phosphors for white light emitting diodes
Applied Physics Letters, 2006Co-Authors: Rongjun Xie, Mamoru Mitomo, Naoto Hirosaki, Ken Sakuma, Naoki KimuraAbstract:Eu2+-activated Li-α-Sialon is a promising yellow phosphor for white light-emitting diodes (LEDs). This letter reports that the emission of Eu2+ in Li-α-Sialon can be tuned widely (563–586nm) by tailoring the composition or controlling the Eu2+ concentration. The thermal stability of Li-α-Sialon:Eu2+, relying a little on the composition and the Eu2+ concentration, remains high in a wide temperature range (25–200°C). Moreover, the chromaticity of Li-α-Sialon:Eu2+ does not shift with changes in temperature. Using a single Li-α-Sialon:Eu2+ phosphor, highly efficient white LEDs (46–55lm∕W) with different color temperatures (3000–5200K) can be fabricated.
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strong green emission from α Sialon activated by divalent ytterbium under blue light irradiation
Journal of Physical Chemistry B, 2005Co-Authors: Rongjun Xie, Kyota Uheda, Naoto Hirosaki, Yoshinobu Yamamoto, Takayuki Suehiro, M Mitomo, Takashi SekiguchiAbstract:This contribution reports on luminescence properties of divalent ytterbium in α-Sialon at room temperature. Ytterbium-doped α-Sialon powders, with the compositions of (M1-2x/vYbx)m/vSi12-m-nAlm+nOnN16-n (M = Ca, Li, Mg, and Y, v is the valency of M, 0.002 ≤ x ≤ 0.10, 0.5 ≤ m = 2n ≤ 3.5), were synthesized by sintering at 1700 °C for 2 h under 0.5 MPa N2. A single, intense, broad emission band, centered at 549 nm, is observed due to the electronic transitions from the excited state 4f135d to the ground state 4f14 of Yb2+. The luminescence of Yb2+ in α-Sialon occurs at relatively low energy, which is attributable to the large crystal field splitting and nephelauxetic effect due to the nitrogen-rich coordination of Yb2+. The dependence of luminescence properties on the Yb2+ concentration, chemical composition, and annealing is discussed. It is suggested that this novel green phosphor could be applied in white light-emitting diodes (LEDs) when combined with a red phosphor and a blue LED.
