low-energy-cathodoluminescence-for-oxy-nitride-phosphors

Low-energy Cathodoluminescence for (Oxy)Nitride Phosphors

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and ...

National Institute for Materials Science (NIMS)

A warm-white light-emitting diode (LED) without blending of different kinds of phosphors is demonstrated. An approach that consists of a blue LED chip and a wavelength-conversion phosphor is carried out. The phosphor is a newly developed yellowish orange CaEuSiAlON ceramic phosphor with high efficiency. The CIE1931 chromaticity coordinates (x, y) are (0.458, 0.414), the color temperature is 2750 K, and the luminous efficacy of this LED is 25.9 lm/W at room temperature and with a forward-bias current of 20 mA. The chromaticity of the assembled LED is more thermally stable than that of a LED with a conventional oxide phosphor (YAG:Ce) because of the better thermal stability of the oxynitride phosphor.

Warm-white light-emitting diode with yellowish orange SiALON ceramic phosphor.

We have developed a new Ce(3+)-activated nitride phosphor, (La,Ca)(3)Si(6)N(11):Ce(3+), using the gas-reduction-nitridation method. The synthesized (La,Ca)(3)Si(6)N(11):Ce(3+) possesses tunable yellow broadband emission with the dominant wavelength of 577-581 nm and the external quantum efficiency up to ∼42%, under an excitation of 450 nm. Precise steady-state and time-resolved photoluminescence analyses revealed that the only one type of Ce(3+) center is active under the blue-light excitation. By combining the synthesized (La,Ca)(3)Si(6)N(11):Ce(3+) phosphors with the 450-nm InGaN chip, a broad range of white light with the correlated color temperatures of ∼2600-3800 K can be created, demonstrating their promising applicability to the warm-white light-emitting diodes.

Synthesis and photoluminescent properties of (La,Ca)₃Si₆N₁₁:Ce³+ fine powder phosphors for solid-state lighting.

Mn(2+) doped-AlN red phosphors were prepared by the solid-state reaction method. X-ray diffraction, SEM-EDS, photoluminescence and cathodoluminescence were utilized to characterize the prepared phosphor. Under UV light or electron beam excitation, the AlN:Mn(2+) phosphors exhibit a strong red emission centered at 600 nm, which is ascribed to the characteristic (4)T1((4)G)-(6)A1((6)S) transition of Mn(2+). Energy level diagrams were constructed to discuss the photoluminescence and cathodoluminescence processes of the AlN:1% Mn(2+) phosphor. The oxygen-related defects in AlN have great influence on the photoluminescence and cathodoluminescence properties of the AlN:1% Mn(2+) phosphor. The dependence of brightness on accelerating voltage or electric current, the decay behavior of CL intensity under the electron bombardment, and the stability of CIE chromaticity coordinates were investigated in detail. The results indicate that the AlN:Mn(2+) phosphor exhibits a higher brightness, higher color purity, and lower saturation compared to the red Y2O3:Eu(3+) phosphor, which gives the AlN:Mn(2+) phosphor great potential as a red phosphor for full color FEDs.

A novel and high brightness AlN:Mn2+ red phosphor for field emission displays.

Knowing the physicochemical properties of a material is of great importance to design and utilize it in a suitable way. In this paper, we conduct a comprehensive survey of photoluminescence spectra, localized cathodoluminescence, temperature-dependent luminescence efficiency, and applications of Eu(2+)-doped Sr0.5Ba0.5Si2O2N2 in solid-state lighting. This phosphor exhibits a broad emission band with a maximum at 560-580 nm and a full-width at half maximum of 92-103 nm upon blue light excitation, whereas a dual-band emission (i.e., 470 nm and 550 nm) is observed under electron beam irradiation due to perhaps the intergrowth of BaSi2O2N2:Eu(2+) and Sr0.5+σBa0.5-σSi2O2N2:Eu(2+) in each phosphor particle. Under 450 nm blue light irradiation, this yellow phosphor exhibits excellent luminescence properties with absorption, internal and external efficiencies of 83.2, 87.7 and 72.6%, respectively. Furthermore, it also possesses high thermal stability, with the quantum efficiency being decreased by only 4.2% at 150 °C and a high quenching temperature of 450 °C. High-efficiency white LEDs using the title phosphor have a luminous efficacy, color temperature and color rendition of ∼120 lm W(-1), 6000 K and 61, respectively, validating its suitability for use in solid-state white lighting.

Europium(ii)-activated oxonitridosilicate yellow phosphor with excellent quantum efficiency and thermal stability - a robust spectral conversion material for highly efficient and reliable white LEDs.

We demonstrated, for the first time, formation of the Na-α'-GeGaON (NamGe12-(m+n)Gam+nOnN16-n) solid solution, an analogue of the well-established α'-SiAlON system. We successfully synthesized single-phase powder samples by reduction-nitridation of Na2CO3-GeO2-Ga2O3, in the solubility range of m ≈ 0.8-1.7 with n ≈ 0.2-0.3. The Rietveld refinement of powder X-ray diffraction data for Na-α'-GeGaON was conducted on the basis of the space group P31c of α'-SiAlON, and the refinement converged with RB = 1.78% and RF = 1.02% for the composition of Na1.26(1)Ge10.50Ga1.50O0.24(1)N15.76(1), indicating reliably the isomorphism between the SiAlON and GeGaON systems. The results of (23)Na solid-state nuclear magnetic resonance (NMR) spectroscopy clearly showed a single peak at the chemical shift of ∼ 16 ppm, further proving the accommodation of Na in the α'-GeGaON matrix with the expected coordination environment. The synthesized Na-α'-GeGaON exhibited stable photocatalytic activity for the evolution of H2 from water under ultraviolet irradiation, which was comparable to that attained by β-Ge3N4.

Article	Year
Warm-white light-emitting diode with yellowish orange SiALON ceramic phosphor. Optics letters\| PubMed ID: 15455760	2004
Synthesis and photoluminescent properties of (La,Ca)₃Si₆N₁₁:Ce³+ fine powder phosphors for solid-state lighting. ACS applied materials & interfaces\| PubMed ID: 21370831	2011
A novel and high brightness AlN:Mn2+ red phosphor for field emission displays. Dalton transactions (Cambridge, England : 2003)\| PubMed ID: 24526132	2014
Europium(ii)-activated oxonitridosilicate yellow phosphor with excellent quantum efficiency and thermal stability - a robust spectral conversion material for highly efficient and reliable wh... Physical chemistry chemical physics : PCCP\| PubMed ID: 26016417	2015
Na-α'-GeGaON Solid Solution Analogous to α'-SiAlON: Synthesis, Crystal Structure, and Potentiality as a Photocatalyst. Inorganic chemistry\| PubMed ID: 26859045	2016

Takayuki Suehiro

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