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1.
Inorg Chem ; 61(18): 6898-6909, 2022 May 09.
Article in English | MEDLINE | ID: mdl-35475349

ABSTRACT

Bright red-emitting phosphors with high color purity and high photoluminescence quantum yield (PLQY) are highly demanded for the fabrication of high-performance warm-white light-emitting diodes (LEDs). Herein, we demonstrated a novel efficient Eu3+-activated Ca2LaHf2Al3O12 garnet phosphor with excellent luminescence properties for near-ultraviolet (near-UV) excited warm-white LEDs. The Ca2LaHf2Al3O12:Eu3+ phosphors exhibited an intense excitation spectrum in the near-UV region with a maximum around 394 nm, and they produced dazzling red luminescence peaking at 592, 614, 659, and 711 nm due to the 5D0 → 7FJ (J = 1-4) transitions of Eu3+ ions when the excitation wavelength was set at 394 nm. Luminescent properties have been studied as a function of Eu3+ doping concentration, and the highest emission intensity was achieved at 50 mol % Eu3+, while the dipole-dipole interaction brought the concentration quenching effect. The Ca2LaHf2Al3O12:50%Eu3+ sample exhibited CIE chromaticity coordinates of (0.6419, 0.3575) with a color purity of 92.7%, and its PLQY was measured to be 64%. The thermal stability and activation energy of Ca2LaHf2Al3O12:50%Eu3+ phosphors were also discussed and analyzed. Finally, we made a near-UV chip-based white LED device in which the Ca2LaHf2Al3O12:50%Eu3+ phosphor was utilized as a red ingredient. A bright warm-white light emission was realized from this LED device under 80 mA driving current, accompanied by a high color rendering index (CRI) of 88.3, a low correlation color temperature of 3853 K, and good CIE chromaticity coordinates of (0.3909, 0.3934). These results revealed that these red-emitting Ca2LaHf2Al3O12:Eu3+ phosphors have promising application prospect in near-UV-excited warm-white LEDs with high a CRI.

2.
ACS Appl Mater Interfaces ; 14(4): 5643-5652, 2022 Feb 02.
Article in English | MEDLINE | ID: mdl-35075892

ABSTRACT

Phosphor-containing white light-emitting diodes (LEDs) with low color-correlated temperatures (CCTs) and high color rendering indexes (CRIs) are highly desirable for energy-efficient and environmentally friendly solid-state light sources. Here, we report a new and efficient blue light-excited, green-emitting Ce3+-activated CaY2ZrScAl3O12 phosphor, which underpins the fabrication of high-color quality and full-visible-spectrum warm-white LED devices with ultrahigh CRI values (Ra > 96 and R9 > 96). A family of CaY2ZrScAl3O12:Ce3+ phosphors with different Ce3+ dopant concentrations were prepared by high-temperature solid-state synthesis. X-ray diffraction and corresponding Rietveld refinement reveal a garnet structure with an Ia3̅d space group and crystallographic parameters a = b = c = 12.39645(8) Å, α = ß = γ = 90°, and V = 1904.99(4) Å3. Luminescence properties were studied in detail as a function of Ce3+ with the optimal concentration 1% mol. Impressively, CaY2ZrScAl3O12:1%Ce3+ exhibits a broad excitation band from 370 to 500 nm, peaking at ∼421 nm, which is well matched with emission from commercial blue LED chips. Under 421 nm excitation, the CaY2ZrScAl3O12:1%Ce3+ phosphor produces dazzling green light in a wide emission band from 435 to 750 nm (emission peak: 514 nm; full width at half-maximum: 113 nm), with a high internal quantum efficiency of 63.1% and good resistance to thermal quenching (activation energy of 0.28 eV). A white LED device combining a 450 nm blue LED chip with CaY2ZrScAl3O12:1%Ce3+ green phosphor and commercial CaAlSiN3:Eu2+ red phosphor as color converters demonstrates bright warm-white light with excellent CIE color coordinates of (0.3938, 0.3819), low CCT of 3696 K, high CRI (Ra = 96.9, R9 = 98.2), and high luminous efficacy of 45.04 lm W-1 under a 20 mA driving current. New green phosphors enable the design and implementation of efficient luminescent materials for healthy solid-state lighting.

3.
J Colloid Interface Sci ; 601: 365-377, 2021 Nov.
Article in English | MEDLINE | ID: mdl-34087597

ABSTRACT

White light-emitting diodes (LEDs) are widely used in lighting and display devices, and the exploration of phosphors with excellent luminescence performance and good stability is the key to the development of white LEDs. In this work, we reported novel near-UV-excited green-emitting Ca2LuHf2(AlO4)3:Ce3+,Tb3+ garnet phosphors with efficient Ce3+ â†’ Tb3+ energy transfer. The CLHA:Ce3+,Tb3+ green phosphors were successfully synthesized by a high-temperature solid-state method, and the phosphors were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence excitation and photoluminescence spectra, the Commission International de I'Eclairage (CIE) chromaticity coordinates, quantum efficiency and temperature-dependent emission spectra. Due to the spin-allowed 4f â†’ 5d transition of Ce3+ ions, the CLHA:Ce3+,Tb3+ phosphors exhibited a strong broad excitation band in the 300-470 nm near-ultraviolet (near-UV) range. Under 408 nm excitation, the CLHA:Ce3+,Tb3+ phosphors showed strong green light with emission center at 543 nm. The mechanism of energy transfer from Ce3+ to Tb3+ ions was attributed to quadruple-quadruple interaction. Impressively, the internal quantum efficiency and external quantum efficiency of the optimal CLHA:0.02Ce3+,0.5Tb3+ green phosphors were measured to be 77.1% and 55.8%, respectively. Finally, using the CLHA:0.02Ce3+,0.5Tb3+ phosphors as green-emitting color converter, a near-UV-pumped white LED device was fabricated, and under 80 mA driving current the LED device demonstrated bright warm-white light with high color rendering index (93.7), low correlated color temperature (3574 K), CIE chromaticity coordinates (0.3922, 0.3633), and high luminous efficacy (29.35 lm/W).

4.
ACS Omega ; 4(8): 13474-13480, 2019 Aug 20.
Article in English | MEDLINE | ID: mdl-31460476

ABSTRACT

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.

5.
RSC Adv ; 9(6): 3429-3435, 2019 Jan 22.
Article in English | MEDLINE | ID: mdl-35518958

ABSTRACT

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).

6.
RSC Adv ; 9(6): 3303-3310, 2019 Jan 22.
Article in English | MEDLINE | ID: mdl-35518995

ABSTRACT

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.

7.
RSC Adv ; 8(48): 27144-27151, 2018 Jul 30.
Article in English | MEDLINE | ID: mdl-35539995

ABSTRACT

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.

8.
RSC Adv ; 8(41): 23323-23331, 2018 Jun 21.
Article in English | MEDLINE | ID: mdl-35540142

ABSTRACT

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.

9.
RSC Adv ; 8(41): 23284-23293, 2018 Jun 21.
Article in English | MEDLINE | ID: mdl-35540160

ABSTRACT

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.

10.
RSC Adv ; 8(53): 30223-30229, 2018 Aug 24.
Article in English | MEDLINE | ID: mdl-35546816

ABSTRACT

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.

11.
RSC Adv ; 8(53): 30191-30200, 2018 Aug 24.
Article in English | MEDLINE | ID: mdl-35546826

ABSTRACT

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.

12.
RSC Adv ; 8(53): 30396-30403, 2018 Aug 24.
Article in English | MEDLINE | ID: mdl-35546862

ABSTRACT

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.

13.
RSC Adv ; 8(61): 35187-35194, 2018 Oct 10.
Article in English | MEDLINE | ID: mdl-35547070

ABSTRACT

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.

14.
RSC Adv ; 8(56): 31835-31842, 2018 Sep 12.
Article in English | MEDLINE | ID: mdl-35547514

ABSTRACT

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.

15.
RSC Adv ; 8(56): 32111-32118, 2018 Sep 12.
Article in English | MEDLINE | ID: mdl-35547519

ABSTRACT

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.

16.
RSC Adv ; 8(57): 32948-32955, 2018 Sep 18.
Article in English | MEDLINE | ID: mdl-35547713

ABSTRACT

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.

17.
RSC Adv ; 8(58): 33035-33041, 2018 Sep 24.
Article in English | MEDLINE | ID: mdl-35548111

ABSTRACT

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.

18.
RSC Adv ; 8(58): 33403-33413, 2018 Sep 24.
Article in English | MEDLINE | ID: mdl-35548130

ABSTRACT

The Sm3+ ion singly doped LiCa3ZnV3O12 (LCZV) phosphors were synthesized by a traditional high-temperature solid-state method. The luminescence characteristics of the as-prepared samples were studied by photoluminescence excitation and emission spectra. Under 343 nm excitation, the synthesized phosphors exhibited color controllable emission induced by the efficient energy transfer from VO4 3- groups to Sm3+ ions. Besides, the energy transfer efficiency was revealed to be about 58.4% when the dopant concentration was 4 mol%. By utilizing the as-prepared LCZV:Sm3+ phosphors, commercial BaMgAl10O7:Eu2+ blue-emitting phosphors and a near-ultraviolet light-emitting diode (LED) chip, a white LED device was fabricated. Under an injection current of 100 mA, the packaged LED device emitted pure white light with high color rendering index (88.4) and proper correlated color temperature (4320 K). By analyzing the thermal quenching behavior of the VO4 3- groups and Sm3+ ions, the optical thermometric behavior of the Sm3+-doped LCZV compounds was investigated. The maximum absolute sensor sensitivity and relative sensor sensitivity were found to be 0.25 K-1 and 1.8% K-1, respectively. Additionally, the emitting color of the studied samples was dependent on the temperature. Ultimately, the Sm3+-doped LCZV phosphors were potential candidates for indoor illumination, optical thermometry and safety signals in high temperature environments.

19.
RSC Adv ; 8(55): 31666-31672, 2018 Sep 05.
Article in English | MEDLINE | ID: mdl-35548243

ABSTRACT

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.

20.
RSC Adv ; 8(50): 28538-28545, 2018 Aug 07.
Article in English | MEDLINE | ID: mdl-35548391

ABSTRACT

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.

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