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Elucidating the structure and optimising the photoluminescence properties of Sr2Al3O6F: Eu3+ oxyfluorides for cool white-LEDs
摘要： Herein, Sr2Al3O6F in hexagonal symmetry was synthesized via a solid-state methodology. The X-ray diffraction pattern of Sr2Al3O6F was refined by the Rietveld refinement with lattice parameters a = 17.8232(1) ? and c = 7.2168(0) ?. The stability of the crystal structure is further confirmed from the results of bond valence sums and the global instability index. The theoretical calculations of the electronic and optical behaviors of the Sr2Al3O6F were analyzed by density functional theory and the obtained results of the lattice parameters and direct bandgap were found close to the experimental data. The chemical states and elemental composition of Sr2Al3O6F were also authenticated by X-ray photoelectron spectroscopy (XPS). To evaluate the suitability of the Sr2Al3O6F structure as high efficient red phosphor, a series of Eu3+ doped Sr2-xEuxAl3O6F (x = 0.0 to 0.10) were synthesized, which showed intense red-orange emission (5D0→7F1,2) at UV and blue excitations. The photoluminescence intensity corresponding to 5D0→7F2 transition decreased significantly for x = 0.10 due to the luminescence quenching. Nevertheless, further enhancement in photoluminescence of Sr1.9Al3O6F: Eu0.1 sample was realized with the substitution of 0.1 mol Ba2+ ion for 0.1 mol Sr2+ ion. The various radiative properties of the emission bands were also analyzed through the Judd-Ofelt theory. The optimized Sr1.8Al3O6F: Ba0.1/Eu0.1 phosphor showed high red color purity (> 95%), and moderate thermal stability of around 72% at 150 oC, suggesting that it could be an ideal red component for white-LEDs. A white-LED comprising the commercial yellow phosphor and the optimized sample showed bright white light having the CRI of 80.5%, CCT of 5510 K, and CIE of (0.33, 0.36) indicating that Sr1.8Al3O6F: Ba0.1/Eu0.1 phosphor is an appropriate red component for cool white-LEDs.
关键词： Eu3+-doping,Rietveld refinement,Hexagonal Sr2Al3O6F,density functional theory,white-LEDs,red phosphors
更新于2025-09-19 17:13:59
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Ultrafast preparation of Europium(III) and Terbium(III) activated LaSr2F7 nanoparticles for white LEDs and anti-counterfeiting mark
摘要： Tunable color-emitting LaSr2F7 nanoparticle-based phosphor materials with single- or co-doped trivalent rare-earth ions (Eu3t/Tb3t) were synthesized via an ultrafast chemical precipitation technique. When Eu3t and Tb3t ions were doped into the LaSr2F7 nanoparticles, the photoluminescence behaviors were investigated and showed characteristic red and green emissions in their respective regions. Under 393 nm excitation, the LaSr2F7:xEu3t nanoparticles revealed the dominant red emission band (5D0 / 7F1) of Eu3t ions while the optimum doping concentration was obtained at 0.4 mol, indicating a quantum yield (QY) of 24.5%. Likewise, the LaSr2F7:yTb3t nanoparticles showed the f-f transition of Tb3t ions and an intense green-emission peak at 543 nm (5D4 / 7F5) was observed under 352 nm of excitation wavelength and the predominant doping concentration was 0.5 mol and the QY was estimated to be about 33.4%. By increasing the Eu3t ion concentration in the optimized LaSr2F7:Tb3t phosphors, the color emissions were turned from yellow to red under 365 nm excitation and the existed energy transfer ef?ciency in between the Tb3t and Eu3t ions was analyzed. Furthermore, the red-, green- and warm white-emitting devices were also fabricated by utilizing the optimal single- and co-doped samples for covering NUV chips. Ultimately, the LaSr2F7:Eu3t and LaSr2F7:Tb3t nanoparticles were further applied to a high-security ink for stabile anti-counterfeiting mark.
关键词： White LEDs,Ultrafast synthesis,Anti-counterfeiting mark,Energy transfer
更新于2025-09-19 17:13:59
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Recorded color rendering index in single Ce,(Pr,Mn):YAG transparent ceramics for high-power white LEDs/LDs
摘要： Transparent ceramic (TC) is an incredibly promising color converter for high-power white LEDs/LDs. However, the preparation process of multiple structured TC with high color rendering index (CRI) is complicated and of technical challenge, and the inability of a single structured TC to achieve a high CRI significantly limits its real application. In this study, high quality single structured Ce,(Pr,Mn):YAG TCs with the 'wide peak' and 'narrow peak' red light emission were designed and fabricated by the solid-state reaction and vacuum sintering method. Compared with the emission spectra of the Ce:YAG TC, synchronous doping Pr3+ and Mn2+ ions into Ce:YAG TCs resulted in an inhomogeneous broaden of the full width at half maximum (FWHM) from 91.7 nm to 102.2 nm. Impressively, the CRI of the single Ce,(Pr,Mn):YAG TC based high-power white LEDs was as high as 84.8, and the correlated-color temperature (CCT) of the white LEDs/LDs were 5450 K and 3550 K, respectively. Furthermore, when the addition amounts of Pr3+ and Mn2+ were 0.2 at.% and 0.8 at.%, respectively, the prepared Ce,(Pr,Mn):YAG TC displayed a high quantum efficiency (IQE=48.14%) and an excellent color stability (only 5% fluctuation). Therefore, this work not only shows how to overcome the spectrum deficiencies of single structured TCs that restrains the intrinsic CRI improvement, but also provides a reference for the pursuit of a high luminescent property. It significantly reinforces the understanding of CRI problems of TC based high-power lighting, which is crucial for the real application of white LEDs/LDs.
关键词： color rendering index,Ce,(Pr,Mn):YAG,synchronous doping,high-power white LEDs/LDs,Transparent ceramic
更新于2025-09-19 17:13:59
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Highly efficient near-UV-excitable Ca2YHf2Al3O12:Ce3+,Tb3+ green-emitting garnet phosphors with potential application in high color rendering warm-white LEDs
摘要： Inorganic phosphors with broadband near-ultraviolet (near-UV) excitation and efficient visible emissions are highly important for fabricating high-performance near-UV-pumped white light-emitting diodes (LEDs). Herein, we reported on novel efficient near-UV-excitable Ce3+/Tb3+ ions co-activated Ca2YHf2Al3O12 (CYHA) green-emitting garnet phosphors, which were successfully prepared through a high-temperature solid-state reaction process. X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence, CIE color coordinates, internal and external quantum efficiency, and temperature-dependent emission spectra were used to characterize the samples. Interestingly, due to the efficient energy transfer from Ce3+ to Tb3+ ions in CYHA, the CYHA:Ce3+,Tb3+ samples presented a wide excitation band in the 370-470 nm region peaking around 408 nm owing to the 4f-5d transition of Ce3+ ions, and under 408 nm excitation they showed intense characteristic sharp green emissions around 543 nm corresponding to the 5D4→7F0-6 transitions of Tb3+ ions. The energy transfer mechanism from Ce3+ to Tb3+ ions was ascribed to the quadruple-quadruple interaction, and the energy transfer efficiency reached as high as 93.2%. Notably, the composition-optimized CYHA:0.03Ce3+,0.6Tb3+ sample exhibited high internal quantum efficiency (IQE) of 78.5% and external quantum efficiency (EQE) of 56%, which were much higher than those of the Tb3+ singly-activated CYHA:0.6Tb3+ sample (IQE = 8%, EQE = 2.2%). Finally, a prototype white LED device was made by combining a 400 nm near-UV-emitting LED chip with the phosphor blend of the as-prepared CYHA:0.03Ce3+,0.6Tb3+ green phosphors, commercial BaMgAl10O17:Eu2+ blue phosphors and commercial CaAlSiN3:Eu2+ red phosphors, which emitted bright warm-white light with good CIE chromaticity coordinates of (0.391, 0.356), low correlated color temperature of 3528 K and high color rendering index of 92.3 under 120 mA driven current. This work opens up new opportunities for the development of efficient color converters toward near-UV-pumped warm-white LEDs with high color rendering index.
关键词： white LEDs,green-emitting garnet phosphors,Ce3+/Tb3+ co-activated,near-UV-excitable,energy transfer
更新于2025-09-19 17:13:59
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Efficient green-emitting Ca2GdZr2Al3O12:Ce3+,Tb3+ phosphors for near-UV-pumped high-CRI warm-white LEDs
摘要： In this work, we reported novel efficient Ce3+/Tb3+ co-doped Ca2GdZr2Al3O12 (CGZA) green-emitting phosphors by traditional solid state method. The phase purity, crystal structure, morphology, photoluminescence properties, internal quantum efficiencies (IQEs), and thermal stability of the samples were systematically investigated. The obtained results revealed that there was an obvious spectral overlap between the emission spectrum of Ce3+ singly doped CGZA phosphors and excitation spectrum of Tb3+ singly doped CGZA phosphors, and efficient energy transfer from Ce3+ to Tb3+ ions existed in Ce3+ and Tb3+ co-doped CGZA phosphors. The Ce3+→Tb3+ energy transfer mechanism was ascribed to the dipole-dipole interaction. The CGZA:Ce3+,Tb3+ phosphors exhibited a broad excitation spectrum in the wavelength range of 370-470 nm with a maximum at 408 nm corresponding to the spin-allowed 4f-5d transition of Ce3+ ions. Upon near-ultraviolet (near-UV) excitation at 408 nm, the composition-optimized CGZA:0.02Ce3+,0.8Tb3+ sample showed intense sharp narrow-line emissions at 485, 543, 591, 629, 643, 663, and 679 nm due to the 5D4→7FJ (J = 6-0) transitions of Tb3+ ions, along with a good IQE of 51%. Lastly, a white LED device was fabricated by using as-prepared CGZA:0.02Ce3+,0.8Tb3+ green phosphors, commercial BaMgAl10O17:Eu2+ blue phosphors, and CaAlSiN3:Eu2+ red phosphors, and under 300 mA driven current it gave bright warm-white light with a low correlated color temperature of 3969 K and a high color rendering index (Ra = 91.2). Our work provides a new perspective for the design and fabrication of efficient color conversion materials toward near-UV LED-based warm-white LEDs.
关键词： Garnet,Ce3+ ions,White LEDs,Phosphors,Tb3+ ions,Photoluminescence
更新于2025-09-16 10:30:52
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Lithium ion doping triggered splendid quantum efficiency and thermal stability in Li <sub/>2</sub> SrSiO <sub/>4</sub> : <i>x</i> Eu <sup>2+</sup> phosphors for optical thermometry and high luminous efficiency white-LED
摘要： Eu2+/Li+-Codoped Li2SrSiO4 orange-yellow phosphors were developed for the applications of white light-emitting diodes (white-LEDs) and optical thermometry. Under near-ultraviolet and blue light excitation, the resultant phosphors exhibited the emissions of Eu2+ ions with an optimal doping concentration of 5 mol% and the concentration quenching mechanism was prevailed to be the dipole–quadrupole interaction. Through the incorporation of Li+ ions into the host lattices, the thermal stability and internal quantum efficiency of the synthesized phosphors were boosted. When the excitation wavelengths were 419 and 449 nm, the internal quantum efficiencies of the Eu2+/Li+-codoped Li2SrSiO4 phosphors were increased to 73% and 69%, respectively. The temperature dependent emission spectra were employed to characterize the thermal stability of the studied samples. The white-LED lamps utilizing the Eu2+/Li+-codoped Li2SrSiO4 phosphors as the orange-yellow component exhibited enhanced photoelectric properties. Furthermore, based on the temperature dependent bandwidth of Eu2+ ions, the thermometric performance of the resultant compounds was studied in detail and the maximum sensitivity was 0.049 K?1. The phosphors with multi-excitation wavelengths were suitable for high luminous efficiency white-LEDs and optical thermometers.
关键词： Li2SrSiO4,Eu2+/Li+-codoped,thermal stability,quantum efficiency,phosphors,white-LEDs,optical thermometry
更新于2025-09-16 10:30:52
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Novel multi-wavelength excitable single-component phosphor system for application in white-LEDs
摘要： A novel color-tunable phosphor of BaZnO2:xEu3+ (x=0 to 20 mol%) has been sucessfully prepared via high-temperature calcination method using alkaline earth metal as the charge compensator. Uncommonly, BaZnO2:Eu3+ is a multi-wavelength excitable phosphor due to its wide absorption spectrum ranging 250-550 nm. It shows broad white (400-700 nm), orange (~580 nm) and red (~611 nm) photoluminescence (PL) under 370 nm, 395 nm and 467 nm excitations, respectively and were assigned to one or more 5D0→7FJ (J =1 to 4) transitions of Eu3+ ion. An efficient energy transfer between Zn2+ and Eu3+ has been observed upon systematically increasing the concentration of Eu3+ ion. Scanning Electron Microscopy images indicated elongated rod-like structures with an average diameter of ~20 nm. The chromaticity coordinates (x, y) were found to be positioned at white (0.33, 0.42), orange (0.51, 0.42) and red (0.65, 0.34) regions correspond to 370 nm, 395 nm and 467 nm excitations, respectively. The temperature-dependent luminescence spectrum of BaZnO2:Eu3+ under the excitation of 467 nm was also studied. It exhibited good thermal stability and a marginal drop in photoluminescence intensity by 4.29% at 150oC was observed. The mathematical calculation of the activation energy was approximately 0.20 eV. The results indicate the suitability of the phosphor for LEDs applications, which is otherwise difficult to obtain in single-component system.
关键词： white LEDs,Phosphor,color tunability,photoluminescence
更新于2025-09-16 10:30:52
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Luminescence varied by selective excitation in Eu3+,Tb3+-doped LiSrPO4 phosphors for W-LEDs applications
摘要： Tb3+ and Eu3+-doped LiSrPO4 (LSPO) were produced via a modified sol-gel route. Structural and optical characterization was performed by X-ray diffraction (XRD) and photoluminescence spectroscopy (PL), respectively. The results reveal that the presence of dopants has an effect on the LSPO structure. PL spectra of the LSPO:Tb, Eu (LSPOTE) phosphor consisted of major emission lines associated with 5D3,4-7FJ (J = 3, 4, 5 and 6) and 5D0-7FJ (J = 0, 1, 2, 3 and 4) transitions of Tb3+ and Eu3+ ions, respectively. A change in emission spectra was observed when the excitation wavelength was changed. Under middle-ultraviolet excitation (227 nm), the Tb3+ and Eu3+-doped LiSrPO4 phosphor exhibited white emission. The results suggest that the LiSr0.97PO4:Tb0.01,Eu0.02 phosphors prepared in the present work could be used in combination with AlGaN chips to fabricate white LEDs.
关键词： Terbium,Lithium strontium orthophosphate,Europium,White LEDs
更新于2025-09-16 10:30:52
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Transition metal ion Co-Doped MgO–MgF2-GeO2:Mn4+ red phosphors for white LEDs with wider color reproduction gamut
摘要： Mn4+-activated non-rare-earth based red phosphors are excellent down conversion materials for phosphor-converted light-emitting diode (pc-LEDs) based solid-state lighting applications. However, the low quantum efficiency of Mn4+ activated red phosphors under InGaN based blue LED excitation hinders their use in phosphor-converted LEDs. To enhance the absorption at an excitation wavelength of around 420 nm in Mn4+-doped MgO-MgF2-GeO2 (MGF: Mn4+), which is a conventional red-emitting lamp phosphor, we doped MGF: Mn4+ phosphors with transition metal oxides (Sc2O3, Lu2O3, Y2O3, and La2O3) replacing MgO. When excited using 420 nm light, the absorption ratio of the synthesized phosphors with Sc2O3 (Sc-MGF:Mn4+) was 58% with an internal quantum efficiency (IQE) of 55% as compared to the 35% IQE of the pristine MGF-Mn4+ phosphor. White LEDs were fabricated using Sc-MGF-Mn4+ (red), and β-SiAlON:Eu2+ (green) on InGaN chips (λem = 450 nm) and their performance was compared to the optical performance of LEDs fabricated using K2SiF6:Mn4+ as the red phosphor. According to the National Television System Committee (NTSC) standard, the color reproduction coverage with an Sc-MGF:Mn4+ phosphor-loaded white LED was 121% by the International Commission on Illumination (CIE) 1976, and 80% by the BT.2020 standard. The coverages are 9% and 6% higher than the coverages of LEDs fabricated using K2SiF6:Mn4+ as the red phosphor according to the NTSC and BT.2020 standards, respectively. Our simple approach to enhance the IQE of Mn4+ activated phosphors by co-doping transition metal oxides can be extended to other Mn4+ activated phosphor systems for applications that require enhanced absorption, higher luminescent emission intensity, and a wider gamut of color reproduction.
关键词： MgO-MgF2-GeO2,Mn4+ activated red phosphors,Solid-state lighting,White LEDs,BT.2020
更新于2025-09-12 10:27:22
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Energy transfer and tunable photoluminescence of Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors for near-UV white LEDs
摘要： A series of apatite-type Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors have been successfully synthesized by the high-temperature solid-state reaction method. Phase structures were examined based on X-ray diffraction, the results indicated that the obtained Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ samples were well crystallized without impurity phase. The photoluminescence emission and excitation spectra and the decay curves were investigated in detail. The main energy transfer from Tb3+ to Eu3+ was verified to compliance with the dipole-quadrupole mechanism. The luminescence colors of the Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors can be easily tuned from green light (0.2570, 0.3766) to white light (0.3674, 0.2813) by adjusting the proportion of Tb3+ and Eu3+ ions. The investigations indicated that the Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors can be used as a qualified candidate for application in white light-emitting diodes.
关键词： Near-UV white LEDs,Phosphors,Sr6Gd2Na2(PO4)6F2:Tb3+,Energy transfer,Photoluminescence,Eu3+
更新于2025-09-12 10:27:22