ChemInform Abstract: Color Point Tuning for (Sr,Ca,Ba)Si2O2N2:Eu2+for White Light LEDs (original) (raw)
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Color Point Tuning for (Sr,Ca,Ba)Si2O2N2:Eu2+ for White Light LEDs
Chemistry of Materials, 2008
Color point tuning is an important challenge for improving white light LEDs. In this paper, the possibilities of color tuning with the efficient LED phosphor Sr 1-x-y-z Ca x Ba y Si 2 O 2 N 2 :Eu z 2+ (0 e x, y e 1; 0.005 e z e 0.16) are investigated. The emission color can be tuned in two ways: by changing Eu 2+ concentration and by substitution of the host lattice cation Sr 2+ by either Ca 2+ or Ba 2+. The variation in the Eu 2+ concentration shows a red shift of the emission upon increasing the Eu concentration above 2%. The red shift is explained by energy migration and energy transfer to Eu 2+ ions emitting at longer wavelengths. Along with this (desired) red shift there is an (undesired) lowering of the quantum efficiency and the thermal quenching temperature due to concentration quenching. Partial substitution of Sr 2+ by either Ca 2+ or Ba 2+ also results in a red-shifted Eu 2+ emission. For Ca 2+ this is expected and the red shift is explained by an increased crystal field splitting for Eu 2+ on the (smaller) Ca 2+ cation site. For Ba 2+ , the red shift is surprising. Often, a blue shift of the fd emission is observed in case of substitution of Sr 2+ by the larger Ba 2+ cation. The Eu 2+ emission in the pure BaSi 2 O 2 N 2 host lattice is indeed blue-shifted. Temperature dependent luminescence measurements show that the quenching temperature drops upon substitution of Sr by Ca, whereas for Ba substitution, the quenching temperature remains high. Color tuning by partial substitution of Sr 2+ by Ba 2+ is therefore the most promising way to shift the color point of LEDs while retaining the high quantum yield and high luminescence quenching temperature.
Journal of Solid State Chemistry, 2008
The influence of the replacement of Sr by Ca on structural and luminescence properties of Eu 2+-doped Sr 2 Si 5 N 8 is reported. The Rietveld refinement of the powder X-ray diffraction data shows that the Ca 2+ ion preferentially occupies the larger Sr site in Sr 2 Si 5 N 8 :Eu 2+. Although the excitation spectrum is hardly modified, the position of the emission band of Eu 2+ can be tailored through partial replacement of Sr by Ca in Sr 2 Si 5 N 8 :Eu 2+ , resulting in red-emission shifting from 620 to 643 nm. Furthermore, (Sr, Ca) 2 Si 5 N 8 :Eu 2+ shows high potential as a conversion phosphor for white-light LED applications due to similar absorption, conversion efficiency and thermal quenching behaviour for 465 nm excitation after the introduction of the Ca ion.
Host sensitized tunable luminescence of single phase white light emitting Ca2Sb2O7:Eu3+ phosphors
Journal of Materials Science: Materials in Electronics, 2019
A series of Eu 3+ doped calcium antimonate (Ca (2−x) Sb 2 O 7 :xEu 3+ , x = 0, 0.05, 0.07, 0.09, 0.1, 0.2 mol%) phosphors were synthesized via high-temperature solid-state reaction method. The structural and optical characterizations of the prepared samples were done using X-ray diffraction (XRD), scanning electron microscope (SEM), ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectroscopy, photoluminescence excitation and emission spectra, and luminescence decay measurements of the phosphors. X-ray diffraction spectrum confirmed the phase purity and orthorhombic weberite structure of the samples. Excitation spectrum suggests that the prepared phosphors can be effectively excited by UV (300 nm/330 nm), NUV (393 nm) and blue (464 nm) light-emitting diodes (LEDs). Under 330 nm ultraviolet excitation, calcium antimonate host exhibits a broad blue emission band, while Eu 3+ doped Ca 2 Sb 2 O 7 samples exhibit blue emission band of host and characteristic emission bands of Eu 3+ ions resulting in a tunable near white light emission. The energy transfer mechanism from host to activator ions is explained. Under rare earth excitations of 393 nm and 464 nm, the samples exhibit strong reddishorange emission. Concentration dependence of emission intensity was studied and the critical energy transfer distance of Eu 3+ ions in Ca (2−x) Sb 2 O 7 :xEu 3+ phosphors was calculated. The concentration quenching of emission intensity was found to be due to dipole-dipole interaction. The Commission International de L'Eclairage coordinates (CIE), color purity, correlated color temperature (CCT), and luminescence lifetimes of the samples were also evaluated. The results indicate that through careful engineering of the dopant concentration and also by changing the excitation wavelength, emission color can be tuned from red to white which envisages the prepared phosphors as a promising candidate in solid-state lighting and display fields.
Emission color variation of (Ba,Sr)_3BP_3O_12:Eu^2+ phosphors for white light LEDs
Optics Express, 2010
A series of alkaline earth borophosphate phosphors, (Ba,Sr) 3 BP 3 O 12 doped with Eu 2+ ions, were synthesized by a solid state reaction. Two emission bands at 465 nm and 520 nm were attributed to the f-d transitions of doped Eu 2+ ions occupying in two different cation sites in host lattices and emission color variation was observed by substituting the M 2+ sites, which was rationalized in terms of two competing factors of the crystal field strength and bond covalence. Green and bluish-white pc-LEDs were fabricated by combination of a 370 nm near-UV chip and composition-optimized Ba 3 BP 3 O 12 :Eu 2+ and (Ba,Sr) 3 BP 3 O 12 :Eu 2+ phosphors, respectively. The series of phosphors may serve as a promising green and bluish-white luminescent materials used in fabrication of near UV-based white pc-LEDs.
Study of Ba2Li2Si2O7:Eu 2+ phosphor for enhancing the luminous flux of white LEDs
TELKOMNIKA, 2023
The best spectrum characteristics and photometric productivities of white light emitting diode (WLED) device possessing light emitting diodes (LEDs) in red rather than phosphor pc/R-WLEDs with the hue fidelity index () > 97 for correlated color temperatures (CCTs) between 2700 K and 6500 K were attained using the illumination effectiveness (LE) model. We demonstrate four practical pc/R-WLEDs that have indices of and LE of 96-97 and 120-124 lm/W, respectively, under CCT values measured at 2969 K, 4468 K, 5682 K, as well as 6558 K. These LED packages use blue and red LEDs, also phosphors in green as well as yellow, with respective wavelengths of 448 nm, 650 nm, 507 nm, and 586 nm. In the comparison between phosphor-transformed WLED devices (with phosphor conversion) and quantum-dot WLED devices (QD-WLEDs), pc/R-WLEDs make an outstanding performance in competitiveness for high hue generation, particularly under small CCT values, and could eventually replace current pc-WLEDs.
Journal of the American Ceramic Society, 2010
In this paper, the (Ca, Ba) 3 (VO 4 ) 2 :Eu 31 red phosphors were prepared by the solid-state reaction method for the first time, and the preferable sintered condition was obtained at 10501C for 6 h. To improve the luminescence intensity of Ca 2.82 (VO 4 ) 2 :0.12Eu 31 , an attempt was made to replace Ca 21 by Ba 21 . It was found that the substitution of 6.7%-9.9% Ba 21 ions instead of the Ca 21 ions enhanced the emission intensity under 465 nm excitation. According to the changes of the lattice constants, this enhancement can originate from the lower site symmetry of the Eu 31 ion in the center with noninversion symmetry. And we observed the optimum value of the Ba 21 content (y) was at 9.9 mol% in (Ca 1Ày Ba y ) 2.82 (VO 4 ) 2 :0.12Eu 31 . Compared with commercial oxysulfide and sulfide red phosphors suitable for blue excitation, our synthesized phosphor (Ca, Ba) 3 (VO 4 ) 2 :Eu 31 has the advantages of no chemical instability or sulfur pollution. In addition, the emission peak at 614 nm and the CIE (International Commission on Illumination) chromaticity points of (0.644, 0.355) for the (Ca 0.901 Ba 0.099 ) 2.82 (VO 4 ) 2 :0.12Eu 31 phosphor indicate this phosphor can be used as a potential candidate for the phosphor-converted white light emitting diode with a blue chip (450-470 nm).
Journal of Alloys and Compounds, 2018
Red emitting Ba 2 Si (5-x) Al x N (8-x) O x :Eu 2+ phosphors were successfully produced by hightemperature solid state reaction method and their luminescence properties were experimentally measured. The analysis of the experimental results suggests that the partial substitution of Al-O for SiN in the host lattice improves the photoluminescence properties and the thermal stability of the produced phosphors. The phosphors exhibited a broad red emission band between 500 and 750 nm. A red shift of emission peak from 588 to 624 nm was recorded with the increase of Al-O content, attributed to the enhancement of stokes shift. The excitation spectrum of the produced phosphors ranged between 200 and 600 nm, covering the UV and the blue region, and suggesting these materials as potentially suitable for use as conversion phosphors for white LED applications in the field of solid state lighting.
Materials Chemistry and Physics, 2011
with a flux, by a conventional solid-state reaction. The optimized red phosphors converted 11.8% (Sc 3+) and 11.7% (Y 3+) of the absorbed blue light into luminescence. These quantum values are much higher than Q = 3.0% of CaS:Eu 2+. For the fabrication of light-emitting diodes (LEDs), the prepared phosphors were coated with MgO from non-aqueous solution to overcome their weakness against moisture. White LEDs were fabricated by pasting the prepared red phosphors and the yellow YAG:Ce 3+ phosphor on an InGaN blue chip (ems = 446.5 nm). The incorporation of the red phosphor to the YAG:Ce 3+ phosphor resulted in an improved color rendering index (Ra) from 70 to 80.
Journal of Luminescence, 2019
In this paper, a series of Bi 3+ and Eu 3+ single-doped as well as Bi 3+ ,Eu 3+ co-doped Ba 9 Y 2 Si 6 O 24 samples were synthesized through a simple high-temperature solid-state reaction method. Their crystal structures, morphologies, luminescent properties, temperature-dependent emission spectra, decay curves and quantum efficiencies were investigated in detail. Upon ultraviolet light excitation, Bi 3+ single-doped samples exhibited blue and green emissions peaking at 408 and 501 nm, corresponding to the 3 P 1-1 S 0 transition of Bi 3+ ions. The spectral analysis indicated that there were two different luminescent centers of Bi 3+ ions due to different occupancies in Ba 9 Y 2 Si 6 O 24 host lattice. And the highest quantum efficiency can reach 64.5% in Ba 9 Y 2 Si 6 O 24 :0.024Bi 3+ phosphor. The remarkable spectral overlap between the emission spectra of Bi 3+ ions and the excitation spectra of Eu 3+ ions indicated the exist of energy transfer from Bi 3+ to Eu 3+. The efficient energy transfer from Bi 3+ to Eu 3+ has been investigated in detail and resulted in that tunable and white-light emission can be obtained by modulating Eu 3+ doping concentration. White emission can be realized with the CIE coordinates of (0.357, 0.345) and quantum efficiency of 57.6% for Ba 9 Y 2 Si 6 O 24 :0.024Bi 3+ ,0.02Eu 3+. The above results demonstrate that Ba 9 Y 2 Si 6 O 24 :Bi 3+ ,Eu 3+ may be a potential candidate for ultraviolet (UV) driven white light-emitting diodes (w-LEDs).