Qi Sun

High-brightness and high-color purity red-emitting Ca 3 Lu(AlO) 3 (BO 3 ) 4 :Eu 3+ phosphors with internal quantum efficiency close to unity for near-ultraviolet-based white-light-emitting diodes

In this work, we reported on high-brightness Eu3+-activated Ca3Lu(AlO)3(BO3)4 (CLAB) red-emitting phosphors. Under 397xa0nm excitation, the CLAB:Eu3+ phosphors showed intense red emissions at around 621xa0nm with CIE coordinates of (0.657, 0.343). The optimal doping concentration of Eu3+ ions was found to be 30xa0mol. %, and the CLAB:0.3Eu3+ sample possessed high-color purity of 93% and ultra-high internal quantum efficiency as great as 98.5%. Importantly, the CLAB:0.3Eu3+ also had good thermal stability. Finally, a white-light-emitting diode (WLED) lamp with good color-rendering index was fabricated by using a 365xa0nm ultraviolet chip and the phosphor blends of CLAB:0.3Eu3+ red-emitting phosphors, (Ba,Sr)2SiO4:Eu2+ green-emitting phosphors, and BaMgAl10O7:Eu2+ blue-emitting phosphors.

Ce3+ and Tb3+ doped Ca3Gd(AlO)3(BO3)4 phosphors: synthesis, tunable photoluminescence, thermal stability, and potential application in white LEDs

Novel blue-green-emitting Ca3Gd(AlO)3(BO3)4:Ce3+,Tb3+ phosphors were successfully synthesized via traditional high temperature solid reaction method. X-ray diffraction, luminescence spectroscopy, fluorescence decay time and fluorescent thermal stability tests have been used to characterize the as-prepared samples. The energy transfer from Ce3+ to Tb3+ ions in the Ca3Gd(AlO)3(BO3)4 host has been demonstrated to be by dipole–dipole interaction, and the energy transfer efficiency reached as high as 83.6% for Ca3Gd0.39(AlO)3(BO3)4:0.01Ce3+,0.6Tb3+. The critical distance was calculated to be 9.44 A according to the concentration quenching method. The emission colour of the obtained phosphors can be tuned appropriately from deep blue (0.169, 0.067) to green (0.347, 0.494) through increasing the doping concentrations of Tb3+. Moreover, the Ca3Gd0.39(AlO)3(BO3)4:0.01Ce3+,0.6Tb3+ phosphor possessed excellent thermal stability at high temperature, and the emission intensity at 423 K was about 87% of that at 303 K. Finally, the fabricated prototype LED device with a BaMgAl10O7:Eu2+ blue phosphor, CaAlSiN3:Eu2+ red phosphor, Ca3Gd0.39(AlO)3(BO3)4:0.01Ce3+,0.6Tb3+ green phosphor and 365 nm-emitting InGaN chip exhibited bright warm white light. The current study shows that Ca3Gd0.39(AlO)3(BO3)4:0.01Ce3+,0.6Tb3+ can be used as a potential green phosphor for white LEDs.

Novel Mn4+-activated LiLaMgWO6 far-red emitting phosphors: high photoluminescence efficiency, good thermal stability, and potential applications in plant cultivation LEDs

Double perovskite-based LiLaMgWO6:Mn4+ (LLMW:Mn4+) red phosphors were synthesized by traditional solid-state route under high temperature, and they showed bright far-red emission under excitation of 344 nm. The crystal structure, luminescence performance, internal quantum efficiency, fluorescence decay lifetimes, and thermal stability were investigated in detail. All samples exhibited far-red emissions around 713 nm due to the 2Eg → 4A2g transition of Mn4+ under excitation of near-ultraviolet and blue light, and the optimal doping concentration of Mn4+ was about 0.7 mol%. The CIE chromaticity coordinates of the LLMW:0.7% Mn4+ sample were (0.7253, 0.2746), and they were located at the border of the chromaticity diagram, indicating that the phosphors had high color purity. Furthermore, the internal quantum efficiency of LLMW:0.7% Mn4+ phosphors reached up to 69.1%, which was relatively higher than those of the reported Mn4+-doped red phosphors. Moreover, the sample displayed good thermal stability; the emission intensity of LLMW:0.7% Mn4+ phosphors at 423 K was 49% of the initial value at 303 K, while the activation energy was 0.39 eV. Importantly, there was a broad spectral overlap between the emission band of LLMW:Mn4+ phosphors and the absorption band of phytochrome PFR under near-ultraviolet light. All of these properties and phenomena illustrate that the LLMW:Mn4+ phosphors are potential far-red phosphors for applications in plant cultivation LEDs.

Synthesis and photoluminescence properties of novel far-red-emitting BaLaMgNbO6:Mn4+ phosphors for plant growth LEDs

A series of far-red-emitting BaLaMgNbO6:Mn4+ (BLMN:Mn4+) phosphors were successfully synthesized by a high-temperature solid-state reaction method. Crystal structure and luminescence properties of the obtained samples were systematically investigated. The emission spectra exhibited a strong narrow far-red emission band peaking at 700 nm with a full width at half-maximum (FWHM) of ∼36 nm under 360 nm excitation. The optimal Mn4+ concentration was about 0.4 mol%. The internal quantum efficiency and CIE chromaticity coordinates of the BLMN:0.4% Mn4+ phosphor were 52% and (0.7222, 0.2777), respectively. In addition, the luminescence mechanism has been analyzed using a Tanabe–Sugano energy level diagram. Finally, by using a 365 nm near-ultraviolet InGaN chip combined with BLMN:0.4% Mn4+ phosphors, a far-red LED device was fabricated.

Novel SrMg2La2W2O12:Mn4+ far-red phosphors with high quantum efficiency and thermal stability towards applications in indoor plant cultivation LEDs

Novel Mn4+-activated far-red emitting SrMg2La2W2O12 (SMLW) phosphors were prepared by a conventional high-temperature solid-state reaction method. The SMLW:Mn4+ phosphors showed a broad excitation band peaking at around 344 nm and 469 nm in the range of 300–550 nm. Under 344 nm near-ultraviolet light or 469 nm blue light, the phosphors exhibited a far-red emission band in the 650–780 nm range centered at about 708 nm. The optimal Mn4+ doping concentration in the SMLW host was 0.2 mol% and the CIE chromaticity coordinates of SMLW:0.2% Mn4+ phosphors were calculated to be (0.7322, 0.2678). In addition, the influences of crystal field strength and nephelauxetic effect on the emission energy of Mn4+ ions were also investigated. Moreover, the internal quantum efficiency of SMLW:0.2% Mn4+ phosphors reached as high as 88% and they also possessed good thermal stability. Specifically, the emission intensity at 423 K still maintained about 57.5% of the initial value at 303 K. Finally, a far-red light-emitting diode (LED) lamp was fabricated by using a 365 nm near-ultraviolet emitting LED chip combined with the as-obtained SMLW:0.2% Mn4+ far-red phosphors.

Photoluminescence properties of a novel rare-earth-free red-emitting Ca 3 Y(AlO) 3 (BO 3 ) 4 :Mn 4+ phosphor for white LEDs application

Novel red-emitting phosphors of Ca3Y(AlO)3(BO3)4 doped with different concentrations of Mn4+ were successfully synthesized by a high-temperature solid-state reaction method. Crystal composition, microstructure, and luminescence properties of samples were characterized by X-ray diffraction, scanning electron microscope, excitation and emission spectra, decay lifetimes and temperature-dependent photoluminescence spectra. The emission spectra exhibited a strong deep-red emission band in the wavelength range of 625–750xa0nm with a maximum at 678xa0nm. The optimal doping concentration of Mn4+ was about 0.1xa0mol%. Under 325xa0nm excitation, the CIE chromaticity coordinates of Ca3Y(AlO)3(BO3)4:0.1%Mn4+ sample were (0.704, 0.296). In addition, the concentration quenching mechanism was dominated by a dipole–dipole interaction for the Mn4+ activators. The value of the activation energy Ea was calculated to explain thermal quenching.

Synthesis and photoluminescence characteristics of high color purity Ba3Y4O9:Eu3+ red-emitting phosphors with excellent thermal stability for warm W-LED application

Single phase Eu3+-activated Ba3Y4O9 (Ba3(Y1−xEux)4O9) red-emitting phosphors with different Eu3+ doping concentrations were synthesized by a high temperature solid-state reaction method. The phase purity, crystal structure, photoluminescence properties, internal quantum efficiency, decay lifetimes, and thermal stability were investigated. Upon excitation at 396 nm near-ultraviolet light and 469 nm blue light, the Ba3(Y1−xEux)4O9 phosphors exhibited a strong red emission at 614 nm due to the 5D0 → 7F2 transition of Eu3+ ions. The optimal doping concentration of Eu3+ ions in Ba3(Y1−xEux)4O9 was found to be x = 0.25. Furthermore, the critical distance was calculated to be 12.78 A and the energy transfer mechanism for the concentration quenching effect was determined to be quadrupole–quadrupole interaction. In addition, the Commission Internationale de IEclairage (CIE) chromaticity coordinates of Ba3(Y0.75Eu0.25)4O9 phosphors were measured to be (0.6695, 0.3302) which located at the red region, and significantly, the high color purity was about 97.9%. The as-synthesized phosphors also possessed excellent thermal stability and the activation energy was determined to be 0.29 eV. Therefore, the investigated results indicated that the Ba3Y4O9:Eu3+ phosphor may be a suitable candidate as a red phosphor for white light-emitting diodes under effective excitation at near-ultraviolet and blue light.

Preparation, characterization, and luminescence properties of double perovskite SrLaMgSbO6:Mn4+ far-red emitting phosphors for indoor plant growth lighting

Mn4+-activated SrLaMgSbO6 far-red emitting phosphors with double perovskite structure were prepared by traditional solid-state reaction. The research on the crystal structure of the SrLaMgSbO6:0.8%Mn4+ (SLMS:0.8%Mn4+) phosphors showed that the as-prepared sample was made up of two polyhedrons, [SbO6] and [MgO6]. Under the excitation of 333 nm, the SLMS:0.8%Mn4+ phosphors exhibited an intense far-red emission in the 625–800 nm wavelength range with CIE chromaticity coordinates of (0.733, 0.268), which could match well with the absorption spectrum of phytochrome PFR. The optimal concentration of Mn4+ ions in the SLMS:Mn4+ phosphors was 0.8 mol%. Importantly, the as-prepared SLMS:0.8%Mn4+ phosphors had an internal quantum efficiency of 35%. The thermal stability of SLMS:0.8%Mn4+ phosphors was also investigated, and the activation energy was found to be 0.3 eV. Thus, the Mn4+-activated SLMS phosphors have great potential to serve as far-red emitting phosphors in indoor plant growth lighting.

Thermally stable La2LiSbO6:Mn4+,Mg2+ far-red emitting phosphors with over 90% internal quantum efficiency for plant growth LEDs

In this paper, we reported on the high-efficiency and thermally-stable La2LiSbO6:Mn4+,Mg2+ (LLS:Mn4+,Mg2+) far-red emitting phosphors. Under 338 nm excitation, the composition-optimized LLS:0.3%Mn4+,1.6%Mg2+ phosphors which were made up of [SbO6], [LiO6], and [LaO8] polyhedrons, showed intense far-red emissions peaking at 712 nm (2Eg → 4A2g transition) with internal quantum efficiency as high as 92%. The LLS:0.3%Mn4+,1.6%Mg2+ phosphors also exhibited high thermal stability, and the emission intensity at 423 K only reduced by 42% compared with its initial value at 303 K. The far-red light-emitting device has also been made by using the LLS:0.3%Mn4+,1.6%Mg2+ phosphors and a 365 nm emitting InGaN chip, which can emit far-red light that is visible to the naked eye. Importantly, the emission spectrum of the LLS:0.3%Mn4+,1.6%Mg2+ phosphors can match well with the absorption spectrum of phytochrome PFR, indicating the potential of these phosphors to be used in plant growth light-emitting diodes.

Synthesis, structure, and luminescence characteristics of far-red emitting Mn4+-activated LaScO3 perovskite phosphors for plant growth

Far-red emitting phosphors LaScO3:Mn4+ were successfully synthesized via a high-temperature solid-state reaction method. The X-ray powder diffraction confirmed that the pure-phase LaScO3:Mn4+ phosphors had formed. Under 398 nm excitation, the LaScO3:Mn4+ phosphors emitted far red light within the range of 650–800 nm peaking at 703 nm (14u2006225 cm−1) due to the 2Eg → 4A2g transition, which was close to the spectral absorption center of phytochrome PFR located at around 730 nm. The optimal doping concentration and luminescence concentration quenching mechanism of LaScO3:Mn4+ phosphors was found to be 0.001 and electric dipole–dipole interaction, respectively. And the CIE chromaticity coordinates of the LaScO3:0.001Mn4+ phosphor were (0.7324, 0.2676). The decay lifetimes of the LaScO3:Mn4+ phosphors gradually decreased from 0.149 to 0.126 ms when the Mn4+ doping concentration increased from 0.05 to 0.9 mol%. Crystal field analysis showed that the Mn4+ ions experienced a strong crystal field in the LaScO3 host. The research conducted on the LaScO3:Mn4+ phosphors illustrated their potential application in plant lighting to control or regulate plant growth.