Salt-assisted combustion synthesis of Ca-α-SiAlON:Eu2+ phosphors

Saito, Genya; Niu, Jing; Yi, Xuemei; Kunisada, Yuji; Sakaguchi, Norihito; Akiyama, Tomohiro

doi:10.1016/j.jallcom.2016.04.211

Cited by 12 publications

(7 citation statements)

References 42 publications

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“…Because the nitridation of Si and Al is exothermic, combustion occurs continuously within a few tens of seconds of ignition, and external heating after ignition is not necessary. Previous studies of Ca-α-SiAlON:Eu 2+ combustion synthesis have clarified the effects of NaCl [15,16], NH 4 Cl [17] and initial composition [18]. These reports have demonstrated the efficiency of this method of Ca-α-SiAlON:Eu 2+ synthesis.…”

Section: Introductionmentioning

confidence: 75%

“…When only pure Al and Si are used as raw materials, the combustion temperature becomes extremely high, which causes particle sintering. In our previous work, NaCl was used as a diluent because the heat released from the nitridation of Al is reduced by the NaCl (solid) → NaCl (liquid) reaction (ΔH = 82.1 kJ/mol) [15,16,27]. Use of NaCl can decrease particle size by suppressing sintering.…”

Section: Effect Of Ca Concentrationmentioning

confidence: 99%

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Combustion synthesis of Ca-α-SiAlON:Eu2+ phosphors with different Ca concentrations and diluent ratios

Saito

Kunisada

Sakaguchi

et al. 2017

Ceramics International

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Yellow Ca-α-SiAlON:Eu 2+ phosphors for white light-emitting diodes (LEDs) were synthesized by a facile combustion synthesis method using CaO, Eu 2 O 3 , α-Si 3 N 4 , Si, and Al as raw materials. Ca concentrations and diluent ratios were optimized to improve their luminescence properties. The lattice constant and luminescence properties improved as x increased from 0.4 to 1.2 in Ca x Si 12−(m+n) Al m+n O n N 16−n :Eu 0.06 . The optimum value was x = 1.2. Scanning transmission electron microscopy combined with energy dispersive X-ray analysis detected segregation of Ca and Eu at grain boundaries, which decreased luminescence behavior in the x = 1.4 sample. The influence of Si and Si 3 N 4 diluents was investigated by varying the diluent ratio φ = ). Changes in temperature and flame propagation speed were measured during combustion synthesis using two thermocouples. When φ was less than 0.5, the combustion temperature exceeded 1600 °C and the synthesized material contained an amount of the high-temperature β-SiAlON phase. At φ > 0.7, the reaction temperature fell below 1200 °C, and unreacted raw materials remained. The optimum value of φ was 0.6. The internal quantum efficiency of the product synthesized at x = 1.2 and φ = 0.6 was approximately 35% under 450-nm excitation. According to electron probe X-ray microanalysis, composition varied within individual synthesized particles, which may explain the decrease in emission behavior relative to a commercial product.

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Section: Introductionmentioning

confidence: 75%

Section: Effect Of Ca Concentrationmentioning

confidence: 99%

Combustion synthesis of Ca-α-SiAlON:Eu2+ phosphors with different Ca concentrations and diluent ratios

Saito

Kunisada

Sakaguchi

et al. 2017

Ceramics International

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“…PL spectra shown in Figure 1a again support the current knowledge that the low electronegativity of N 3− and the high covalency of the Eu−N bond, i.e., nephelauxetic effect, result in the long-wavelength broad emission attributed to the allowed transition of 4f 6 5d−4f 7 ( 8 S) of Eu 2+ . 21,31 In order to confirm the nature of the sharp lines ranging 400−500 nm, we acquired excitation spectrum under monitoring 560 nm emission wavelength where the supposed Eu 3+ emission is not available (as shown in Figure S2). While similar sharp lines still appear in the same region, it indicates that these sharp lines should originate from a Xe lamp.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Most of the studies on Ca-α-SiAlON:Eu focused on the synthesis methods aimed at liberating the harsh synthetic conditions, such as gas pressure sintering, gas/carbothermic reduction nitrogen method, − and salt-assisted combustion. , However, two issues which are vital to understanding the actual luminescence mechanism and practical application have been paid less attention: First, the oxidation states of Eu in the low concentration doping system is pending, perhaps due to lack of fine testing instruments. Therefore, albeit band-shaped emission spectra , typical of 4f–5d transitions of Eu 2+ are found, one cannot exclude the possible coexistence of mixed valences of Eu, which may provoke interest in investigating the effects of Eu ions of different valences on photoluminescence properties.…”

Section: Introductionmentioning

confidence: 99%

Ca-α-SiAlON:Eu Phosphors: Oxidation States, Energy Transfer, and Emission Enhancement by Incorporation-Aimed Surface Engineering

Chen

Gan

Zhang

et al. 2017

ACS Appl. Mater. Interfaces

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Ca-α-SiAlON:Eu is one of the most promising phosphors exhibiting potential applications in high power LEDs owing to its excellent thermal stability and relatively high luminescence efficiency comparable to YAG:Ce commercial phosphors. The oxidation states of Eu ions in Ca-α-SiAlON:Eu are still questionable, and furthermore it exhibits lower luminescence intensity than commercial yellow phosphors. Therefore, in the present work, the valences of Eu ions in Ca-α-SiAlON have been examined, from which a mixture of divalence and trivalence is observed. Further improvement in emission intensity involves finding a way to increase the incorporation of larger Eu ions into the Ca-α-SiAlON. Here, we observed preferred doping of Eu around phosphor grain surface and then propose a surface engineering strategy involving HF pickling of glassy surface layer, formation of Eu-rich precursors, and finally post-annealing, aiming to increase surface incorporation of Eu ions. The surface engineered samples exhibit great enhancement in emission intensity with a maximum increment by 80%.

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“…Because the nitridation of Al is exothermic, combustion occurs continuously within a few tens of seconds of ignition, and thereafter, external heating is unnecessary. This method has the advantages of low energy consumption and short reaction times, and has been applied to produce a variety of advanced materials, including AlN, Ca–α–SiAlON, β–SiAlON, Si 3 N 4 , and YAG . In this study, we examine the effects of the Al and carbon ratios on the synthesized AlN.…”

Section: Introductionmentioning

confidence: 99%

Combustion synthesis of AlN doped with carbon and oxygen

et al. 2018

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Carbon-and-oxygen-doped AlN specimens were prepared by combustion synthesis using Al, graphite, and AlN. Graphite addition changed the product color from white to blue. By XRD, the lattice constant increased slightly with increasing carbon content. Blue AlN powder was synthesized with a molar ratio of the diluent AlN of 0.2-0.5 with a fixed graphite content of 0.05. At an AlN molar ratio exceeding 0.6, carbon was not successfully incorporated due to the lower reaction temperature. Calcination at 800°C in air removed residual graphite without changing the crystal structure or product color. Oxygen, nitrogen, and carbon analyses revealed that blue AlN powders contained 0.45-0.54 mass% carbon and 1.4-1.6 mass% oxygen, while the undoped AlN contained 0.021 mass% carbon and 0.94 mass% oxygen. The origin of the white-to-blue color change was investigated via reflection measurements. Blue AlN exhibits an absorption peak at 634 nm (1.96 eV). From first-principles electronic structure calculations, the C-doped AlN and carbon-and-oxygen-doped AlN with a 1:1 ratio could be classified as p-type, whereas the O-doped AlN and 1:3 carbon-and-oxygen-doped AlN were n-type.One reason for the absorption peak at 634 nm may be a transition from the conduction band to an upper unoccupied state. These results suggest the possible control of optical and electronic properties of AlN via carbon-and-oxygen doping. K E Y W O R D Saluminum nitride, combustion synthesis, dopants/doping

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Salt-assisted combustion synthesis of Ca-α-SiAlON:Eu2+ phosphors

Cited by 12 publications

References 42 publications

Combustion synthesis of Ca-α-SiAlON:Eu2+ phosphors with different Ca concentrations and diluent ratios

Combustion synthesis of Ca-α-SiAlON:Eu2+ phosphors with different Ca concentrations and diluent ratios

Ca-α-SiAlON:Eu Phosphors: Oxidation States, Energy Transfer, and Emission Enhancement by Incorporation-Aimed Surface Engineering

Combustion synthesis of AlN doped with carbon and oxygen

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