Synthesis, Crystal Structure, and Photoluminescence Characteristics of High-Efficiency Deep-Red Emitting Ba2GdTaO6:Mn4+ Phosphors.

In this article, a series of novel Mn4+-doped Ba2GdTaO6 (BGT) red-emitting phosphors were successfully synthesized via a high-temperature solid-state method. The crystal structure, morphology, and luminescent performance of the samples were investigated in detail with X-ray diffraction, field emission scanning electron microscopy, photoluminescence (PL) spectra, decay curves, and internal quantum efficiency (IQE). Excited at 358 nm, these samples showed an intense deep-red emission band peaking at 688 nm in the wavelength region of 620-800 nm. The excitation spectra of these samples monitored at 688 nm exhibited two broad excitation bands from 250 to 600 nm with peaks at 358 and 469 nm. The systematic investigation of the concentration-dependent PL properties of BGT:Mn4+ phosphors revealed that the deep-red emission intensity reached the maximum when the Mn4+ doping concentration was 0.6 mol %. The critical distance (R c) between Mn4+ ions for concentration quenching was 36.57 Å, and the major mechanism of energy transfer among Mn4+ activators in BGT:Mn4+ was dipole-dipole interaction. The decay lifetimes decreased from 0.285 to 0.248 ms with the increasing Mn4+ doping concentration from 0.2 to 1.2 mol %. The Commission Internationale de l'Éclairage coordinates of the optimal BGT:0.6%Mn4+ sample were (0.7294, 0.2706). The values of the IQE for all BGT:Mn4+ samples were measured, and the highest value could reach up to 62%. The above results revealed that these high-efficiency BGT:Mn4+ deep-red-emitting phosphors had promising potential for application in indoor plant growth lighting.

Mn4+-activated Li3Mg2SbO6 as an ultrabright fluoride-free red-emitting phosphor for warm white light-emitting diodes.

In this paper, we report on highly efficient Mn4+-activated double perovskite Li3Mg2SbO6 (LMS) red-emitting phosphors. These LMS:Mn4+ phosphors can be efficiently excited over a broad wavelength band from 235 nm to 600 nm peaking at 344 nm and 469 nm, and exhibited an intense red emission band with a range from 600 nm to 800 nm centered around 651 nm. The optimal Mn4+ doping concentration of LMS:Mn4+ was 0.6 mol% and its internal quantum efficiency can reach as high as 83%. Besides, the thermal quenching effect on the optical property was also analyzed. Finally, a warm white light-emitting diode (WLED) lamp was fabricated by using a 454 nm InGaN blue LED chip combined with a blend of YAG:Ce3+ yellow phosphors and the as-prepared LMS:0.6% Mn4+ red phosphors, which showed bright white light with CIE chromaticity coordinates (0.4093, 0.3725), correlated color temperature (CCT = 3254 K), color rendering index (CRI = 81) and luminous efficacy (LE = 87 lm/W).

Mn4+-activated BaLaMgSbO6 double-perovskite phosphor: a novel high-efficiency far-red-emitting luminescent material for indoor plant growth lighting.

In the present work, novel high-efficiency Mn4+-activated BaLaMgSbO6 (BLMS) far-red-emitting phosphors used for plant growth LEDs were successfully synthesized via a solid-state reaction method. X-ray diffraction (XRD), photoluminescence (PL), temperature-dependent PL, CIE color coordinates, and lifetimes as well as internal quantum efficiency (IQE) were used to characterize the phosphor samples. The excitation spectrum of the as-obtained BLMS:Mn4+ phosphors presented two wide bands covering 250-550 nm and the emission spectrum exhibited a far-red emission band in the range of 650-800 nm peaked at 700 nm. Concentration-dependent PL properties of BLMS:Mn4+ phosphors were studied. The optimal doping concentration of Mn4+ ions was 0.6 mol%, and the concentration quenching mechanism was determined to be the nonradiative energy transfer among the nearest-neighbor Mn4+ activators. Impressively, the BLMS:0.6%Mn4+ sample showed an outstanding IQE of 83%. In addition, luminescence thermal quenching characteristics were also analyzed. Furthermore, the PL spectrum of BLMS:0.6%Mn4+ sample was compared with the absorption spectrum of phytochrome PFR. Finally, after combining BLMS:0.6%Mn4+ phosphors with a 365 nm near-UV LED chip, a far-red light-emitting diode (LED) device was successfully achieved to demonstrate its possible applications in plant growth LEDs.

High-efficiency cubic-phased blue-emitting Ba3Lu2B6O15:Ce3+ phosphors for ultraviolet-excited white-light-emitting diodes.

In this work, Ce3+-activated Ba3Lu2B6O15 (BLBO) blue-emitting phosphors were prepared, and their photoluminescence properties were studied. It was found that these phosphors can be excited over a broad excitation band range from 300 nm to 430 nm and generated a blue emission band in the 400-550 nm range with a maximum peak at 443 nm. The full width at half maximum of the blue emission band was about 68 nm. The optimal doping concentration of Ce3+ ions was determined to be 3 mol. %, and the BLBO:0.03Ce3+ phosphors possessed an internal quantum efficiency as high as 71%. Finally, by coating the phosphors with a blend of commercial CaAlSiN3:Eu2+ red-emitting phosphors, (Ba,Sr)2SiO4:Eu2+ green-emitting phosphors, and BLBO:0.03Ce3+ blue-emitting phosphors on a 380 nm ultraviolet light-emitting diode (LED) chip, a white LED device with a color-rendering index of ∼94 and correlated color temperature of 4952 K was obtained.

High-efficiency and thermally stable far-red-emitting NaLaMgWO6:Mn4+ phosphorsfor indoor plant growth light-emitting diodes.

In this Letter, we report a novel NaLaMgWO6:Mn4+ double-perovskite phosphor. Under the excitation at 342 nm, this phosphor showed a high-efficiency far-red emission at approximately 700 nm with internal quantum efficiency of up to 60%. Moreover, it exhibited a high thermal stability; the emission intensity at 423 k was approximately 57% of that at room temperature. Finally, a prototype light-emitting diode (LED) device was fabricated using the combination of a NaLaMgWO6:Mn4+ far-red-emitting phosphor and 365-nm LED chip.

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 P FR 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.

Novel Eu3+-activated Ba2Y5B5O17 red-emitting phosphors for white LEDs: high color purity, high quantum efficiency and excellent thermal stability.

Eu3+-activated Ba2Y5B5O17 (Ba2Y5-x Eu x B5O17; x = 0.1-1) red-emitting phosphors were synthesized by the conventional high temperature solid-state reaction method in an air atmosphere. Powder X-ray diffraction (XRD) analysis confirmed the pure phase formation of the as-synthesized phosphors. Morphological studies were performed using field emission-scanning electron microscopy (FE-SEM). The photoluminescence spectra, lifetimes, color coordinates and internal quantum efficiency (IQE) as well as the temperature-dependent emission spectra were investigated systematically. Upon 396 nm excitation, Ba2Y5-x Eu x B5O17 showed red emission peaking at 616 nm which was attributed to the 5D0 → 7F2 electric dipole transition of Eu3+ ions. Meanwhile, the influences of different concentrations of Eu3+ ions on the PL intensity were also discussed. The optimum concentration of Eu3+ ions in the Ba2Y5-x Eu x B5O17 phosphors was found to be x = 0.8. The concentration quenching mechanism was attributed to the dipole-dipole interaction and the critical distance (R c) for energy transfer among Eu3+ ions was determined to be 5.64 Å. The asymmetry ratio [(5D0 → 7F2)/(5D0 → 7F1)] of Ba2Y4.2Eu0.8B5O17 phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba2Y5-x Eu x B5O17 phosphors. In addition, the CIE color coordinates of the Ba2Y4.2Eu0.8B5O17 phosphors (x = 0.653, y = 0.345) were found to be very close to the National Television System Committee (NTSC) standard values (x = 0.670, y = 0.330) of red emission and also showed high color purity (∼94.3%). The corresponding internal quantum efficiency of the Ba2Y4.2Eu0.8B5O17 sample was measured to be 47.2%. Furthermore, the as-synthesized phosphors exhibited good thermal stability with an activation energy of 0.282 eV. The above results revealed that the red emitting Ba2Y4.2Eu0.8B5O17 phosphors could be potential candidates for application in near-UV excited white light emitting diodes.

Synthesis and characterization of Ca3Lu(GaO)3(BO3)4:Ce3+,Tb3+ phosphors: tunable-color emissions, energy transfer, and thermal stability.

Blue-green dual-emitting phosphors Ca3Lu(GaO)3(BO3)4:Ce3+,Tb3+ (CLGB:Ce3+,Tb3+) were synthesized via a traditional solid-state reaction method. The phase of the phosphors was characterized by X-ray diffraction and the luminescence properties were investigated using the excitation and emission spectra, decay curves, temperature-dependent emission spectra, CIE chromaticity coordinates, and the internal quantum efficiency. Under 345 nm UV light excitation, Ce3+ singly doped CLGB phosphors presented intense blue light in the 350-550 nm wavelength region with a maximum peak at 400 nm. In sharp contrast, CLGB:Ce3+,Tb3+ phosphors showed both the blue and green emission wavelengths of Ce3+ and Tb3+ ions, respectively. The overall emission colors can be tuned from blue (0.164, 0.042) to green (0.331, 0.485) via increasing the concentration of Tb3+ ions, due to the energy transfer (ET) from Ce3+ ions to Tb3+ ions. The optimal doping concentration of Tb3+ ions in CLGB:Ce3+,Tb3+ phosphors was found to be 40 mol%. The mechanism of the ET from the Ce3+ to Tb3+ ions was demonstrated to be electric quadrupole-quadrupole interaction. The CLGB:0.04Ce3+,0.40Tb3+ sample possessed a high IQE of 54.2% and excellent thermal stability with an activation energy of 0.3142 eV when excited at 345 nm. The integrated emission intensity of CLGB:0.04Ce3+,0.40Tb3+ at 423 K was found to be about 74% of that at 303 K. Finally, under 300 mA driven current, the fabricated prototype white light-emitting diode showed CIE chromaticity coordinates of (0.3996, 0.3856) and high color rending index of 81.2. Considering all the above characteristics, the obtained CLGB:Ce3+,Tb3+ phosphors can be a type of multicolor emitting phosphor for application in white light-emitting diodes.

Novel SrLaAlO4:Mn4+ deep-red emitting phosphors with excellent responsiveness to phytochrome PFR for plant cultivation LEDs: synthesis, photoluminescence properties, and thermal stability.

Herein, novel rare-earth-free Mn4+-doped SrLaAlO4 deep-red emitting phosphors were successfully synthesized via a traditional solid-state reaction method. The crystal structure and phase purity of the as-prepared samples were confirmed by XRD Rietveld refinement. Photoluminescence properties of SrLaAlO4:Mn4+ phosphors were examined in detail using photoluminescence spectra, decay lifetimes, temperature-dependent emission spectra and internal quantum efficiency measurements. The excitation spectrum obtained by monitoring at 730 nm contained two excitation bands centered at 364 and 520 nm within the range of 200-550 nm due to the Mn4+-O2- charge-transfer band and the 4A2g → 4T1g, 4T2g transitions of the Mn4+ ions. Under the 364 nm excitation, the SrLaAlO4:Mn4+ phosphors exhibited an intense deep-red emission band in 610-790 nm wavelength range peaking at 730 nm, which was assigned to the 2Eg → 4A2g transition of Mn4+ ions. The deep red emission showed excellent responsiveness to phytochrome PFR, revealing that the SrLaAlO4:0.4% Mn4+ phosphors possessed a possible application in deep-red light-emitting diodes (LEDs) for plant cultivation. The optimal doping concentration of Mn4+ ions was found to be 0.4 mol%. The critical distance R c for energy transfer among Mn4+ ions was determined to be 5.86 Šand the concentration quenching mechanism was confirmed to be the electric dipole-dipole interaction. In addition, the Commission International de I'Eclairage (CIE) colour coordinates of the SrLaAlO4:0.4% Mn4+ phosphors (0.734, 0.266) were located in the deep red region and the corresponding internal quantum efficiency was measured to be about 29%. The above results confirmed that the as-prepared SrLaAlO4:0.4% Mn4+ deep red emitting phosphors might be a potential candidate for plant cultivation LEDs.

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 novel Ba2Lu5B5O17:Eu3+ red emitting phosphors with high color purity for near-UV excited white light emitting diodes.

A series of new red-emitting Ba2Lu4.98-x Eu x La0.02B5O17 (0.1 ≤ x ≤ 1.0) phosphors were synthesized via the high-temperature solid-state reaction method. The phase formation of the as-synthesized Ba2Lu4.48Eu0.5La0.02B5O17 phosphor was confirmed by powder X-ray diffraction analysis. It was found that La3+ doping resulted in the reduction of LuBO3 impurities and thus pure phase Ba2Lu5B5O17 was realised. The morphology of Ba2Lu4.48Eu0.5La0.02B5O17 phosphors was studied by field emission scanning electron microscopy (FE-SEM). As a function of Eu3+ concentration the photoluminescence spectra and decay lifetimes were investigated in detail. Under excitation at 396 nm, a dominant red emission peak located at 616 nm (5D0 → 7F2) indicated that Eu3+ ions mainly occupied low symmetry sites with a non-inversion center in Ba2Lu4.48Eu0.5La0.02B5O17. The optimal Eu3+ ion concentration was found to be x = 0.5 and the critical distance of Eu3+ was determined to be 6.55 Å. In addition, the concentration quenching takes place via dipole-dipole interactions. The phosphors exhibited good CIE (Commission International de I'Eclairage) color coordinates (x = 0.643, y = 0.356) situated in the red region and a high color purity of 97.8%. Furthermore, the internal quantum efficiency and the thermal stability of Ba2Lu4.48Eu0.5La0.02B5O17 phosphors were also investigated systematically. The results suggest that Ba2Lu4.48Eu0.5La0.02B5O17 may be a potential red phosphor for white light-emitting diodes.

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 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-x Eu x )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-x Eu x )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-x Eu x )4O9 was found to be x = 0.25. Furthermore, the critical distance was calculated to be 12.78 Šand the energy transfer mechanism for the concentration quenching effect was determined to be quadrupole-quadrupole interaction. In addition, the Commission Internationale de I'Eclairage (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.

Novel high-efficiency Eu3+-activated Na2Gd2B2O7 red-emitting phosphors with high color purity.

In this study, a series of Na2(Gd1-x Eu x )2B2O7 (abbreviated as: Na2Gd2B2O7:xEu3+; x = 0, 0.05, 0.15, 0.35, 0.45, and 0.50) phosphors were synthesized by conventional solid state reaction approach. The structure and morphology of the as-prepared phosphors were studied by X-ray diffraction, scanning electron microscopy and elemental mapping. The results indicated that the phosphors had micro-size particles with monoclinic phases. The photoluminescence excitation and emission study indicated that the as-prepared phosphors could give rise to efficient red emissions under near-ultraviolet excitation. The optimal doping concentration of Eu3+ ions was x = 0.35, and the corresponding deduced critical distance (R c) was about 9.4 Å. The concentration quenching mechanism was dominated by energy-transfer among the Eu3+ ions through dipole-dipole interactions. The calculated internal quantum efficiency of the Na2Gd2B2O7:0.35Eu3+ red phosphor was 70.8% and the color purity was as high as 99%. Furthermore, decay dynamics revealed that with the increase in the content of Eu3+, the lifetimes decreased due to the increase in non-radiative transition. Importantly, the present Na2Gd2B2O7:0.35Eu3+ phosphors also exhibited good thermal stability, and the emission intensity at 150 °C was about 56% of that at 30 °C. Furthermore, a warm white light-emitting diode (WLED) device was fabricated with commercial BaMgAl10O17:Eu2+ blue phosphors, (Ba,Sr)2(SiO4):Eu2+ green phosphors, and the as-prepared Na2Gd2B2O7:0.35Eu3+ red phosphors as well as a 395 nm LED chip. The device exhibited CIE coordinates of (0.4367, 0.3987), a high color rendering index (CRI = 92.2), a low correlated color temperature (CCT = 2960 K), and a luminous efficacy of 40.65 lm W-1. The observed results strongly indicate that the as-prepared Na2Gd2B2O7:Eu3+ phosphors may be used as the red emitting component in pc-WLEDs.

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 (14 225 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.

Far-red-emitting double-perovskite CaLaMgSbO6:Mn4+ phosphors with high photoluminescence efficiency and thermal stability for indoor plant cultivation LEDs.

A series of Mn4+-activated CaLaMgSbO6 far-red-emitting phosphors were synthesized by a solid-state reaction route and the microstructure and optical characterizations were investigated in detail. Upon excitation at 370 and 469 nm, the samples showed intense far-red emission at about 708 nm originating from the 2Eg → 4A2g transition and the optimal Mn4+ concentration was 0.7 mol%. The as-prepared phosphors also exhibited excellent internal quantum efficiency (88%) and high thermal stability. The emission intensity at room temperature dropped to 54% when the temperature rose to 423 K and the activation energy was 0.34 eV. The outstanding optical properties and the fact that the emission band of the obtained phosphors had a broad overlap with the absorption band of phytochrome P FR demonstrated that the CaLaMgSbO6:Mn4+ phosphors may be promising potential spectral converters for applying to indoor plant cultivation light-emitting diodes.

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.

Lu3+ doping induced photoluminescence enhancement in novel high-efficiency Ba3Eu(BO3)3 red phosphors for near-UV-excited warm-white LEDs.

Ba3Eu(BO3)3 (BEB) and Lu3+ doped BEB red phosphors were successfully synthesized by a high-temperature solid-state reaction method. X-ray diffraction (XRD) patterns, excitation and emission spectra, decay lifetimes, CIE coordinates, internal quantum efficiency, and thermal stability of these phosphors were systematically studied. Under 395 nm excitation, these phosphors exhibited high-brightness red emissions centred at 611 nm. In addition, it was found that doping appropriate amounts of Lu3+ ions into BEB phosphors can improve their photoluminescence intensity and internal quantum efficiency. The integrated emission intensity of BEB:0.3Lu3+ phosphor was about 1.34 times that of BEB phosphor. Compared with commercial red phosphor Y2O2S:Eu3+, BEB:0.3Lu3+ phosphor showed better color purity (91.4%) and higher emission intensity (about 3.25 times). Surprisingly, the BEB:0.3Lu3+ phosphor had a high internal quantum efficiency of almost 87%, which was higher than that of 83% for BEB phosphors. Meanwhile, the BEB:0.3Lu3+ phosphors also exhibited good thermal stability with activation energy around 0.14 eV, and the integrated emission intensity at 423 K remained about 52% of that at 303 K. Finally, by using commercial BaMgAl10O17:Eu2+ blue phosphors, commercial (Ba,Sr)2SiO4:Eu2+ green phosphors, as-prepared BEB:0.3Lu3+ red phosphors and a 395 nm near-ultraviolet-emitting light-emitting diode (LED) chip, a prototype warm white LED device was fabricated, which showed good color rendering index (CRI = 84.7) and low correlated color temperature (CCT = 3377 K).

Novel far-red-emitting SrGdAlO4:Mn4+ phosphors with excellent responsiveness to phytochrome PFR for plant growth lighting.

In this work, we reported on novel far-red-emitting SrGdAlO4:Mn4+ (SGA:Mn4+) phosphors towards application in plant growth lighting. The crystal structure and luminescence properties were investigated on the basis of X-ray diffraction, excitation and emission spectra, luminescence decay curves and temperature-dependent photoluminescence spectra. When excited by 353 nm, the SGA:Mn4+ phosphors showed a far-red emission band in the 650-800 nm wavelength range with peaks at 709 and 725 nm, which was due to the 2Eg → 4A2g electron transition of Mn4+ ion. The optimal Mn4+ doping concentration was about 0.1 mol%. The CIE chromaticity coordinates of the SGA:0.1%Mn4+ sample were (0.7064, 0.2934). The luminescence decay lifetimes decreased gradually from 1.263 to 0.868 ms with the increasing Mn4+ concentrations. Notably, the emission band of SGA:0.1%Mn4+ sample was well-matched with the absorption spectrum of phytochrome PFR, which indicated the SGA:Mn4+ were potential far-red-emitting phosphors for plant growth applications.