Emission tunable of Mg0.695Si0.695Al1.39O3.65N0.35:Eu2+,Mn2+ oxynitride phosphors via energy transfer for WLEDs

doi:10.1016/j.jre.2020.06.021

Journal of Rare Earths

Volume 39, Issue 6, June 2021, Pages 643-650

https://doi.org/10.1016/j.jre.2020.06.021 Get rights and content

Abstract

A series of Eu²⁺ doped and Eu²⁺/Mn²⁺ co-doped Mg_0.695Si_0.695Al_1.39O_3.65N_0.35 (MSAON) phosphors were synthesized by solid-state reaction at a lower temperature of 1500 °C. The crystal morphology and structure of MSAON host were characterized by SEM, TEM and XRD. The quantum yield (QY) for Eu²⁺ doped MSAON phosphors was measured as high as 62%, indicating the excellent luminous efficiency. For the Eu²⁺/Mn²⁺ co-doped MSAON phosphor, the photoluminescence spectrum and delay curves reveal the efficient energy transfer (ET) process from Eu²⁺ to Mn²⁺ ions. Meanwhile, the corresponding energy transfer efficiency, critical distance and mechanism are discussed in detail. Temperature-dependent emission spectrum shows the thermal and color stabilities. The emission color of MSAON:Eu²⁺,Mn²⁺ phosphors could be tuned from blue through white to red via varying the concentration of Mn²⁺ ions. White-light-emitting diodes (WLEDs) were successfully fabricated by encapsulating the phosphors in n-UV LED (365 nm) devices obtaining white light with color rendering index (CRI) as high as 87.7. The results reveal that the MSAON:Eu²⁺,Mn²⁺ phosphors could have potential application in the field of n-UV WLEDs.

Graphical abstract

The color-tunable emission and energy transfer from Eu²⁺ to Mn²⁺ have been discussed for MSAON:Eu²⁺,Mn²⁺ phosphors. The phosphors were encapsulated into LED chips (365 nm) and the brightly white lights are obtained.

Introduction

White light-emitting diodes (LEDs) known as a new generation of solid-state lighting source are widely welcome. Compared with the traditional light source, it has better performances, such as high efficiency, low energy consumption, various color and environmentally friendly characteristics. Recently, there were two commonly used ways to prepare WLEDs.1, 2, 3, 4 The first one was to coat the commercial yellow phosphor Y₃Al₅O₁₂:Ce³⁺ on the blue InGaN LED chip. In the second, the mixture of tricolor phosphors (red, green, blue) was excited with n-UV LED chip to realize white-emitting. However, the disadvantage of the first method was low color rendering index (CRI < 80) and high color temperature (CCT > 4500 K) due to the lack of red component, which was not perfect in display effect.5, 6, 7 As for the second method, the stability of the light will be owing to the different properties of different phosphors. At present, rare earth activated nitrogen oxide phosphors, for instance, Ca-α-SiAlON:Eu²⁺/Mn²⁺,⁸^,⁹ BaSi₃O₄N₂:Eu²⁺/Mn²⁺,¹⁰ β-SiAlON:Eu²⁺,¹¹ γ-AlON,¹² were getting more and more attention owing to their excellent properties, such as strong absorption in the UV that is matched well with the n-UV LED devices, red shift of emission spectrum, and excellent thermal stability.

In recent years, the binary system of Al₂O₃–AlN is widely concerned. The reports about the polymorph of AlON such as Al₅O₃N₃,¹³ Al₁₀O₃N₈,¹⁴ Al₅O₆N¹⁵ show the excellent photoluminescence performance and thermal stability. However, the most phosphors doped with Eu²⁺ ions exhibit narrow band emission in the blue to green range. Thus, adding red emission components was needed for realizing the white light emission.

To overcome the above difficulties, we focused on the study of Al_2.78O_3.65N_0.35 phosphors. It has been reported that a novel AlON polymorph of Mg_1.25Si_1.25Al_2.5O₃N₃ phosphor has been synthesized by co-substituting Al³⁺ with Mg²⁺ and Si⁴⁺ ions.¹⁶ This method not only broadens the emission spectrum, but also effectively reduces the reaction temperature from 1650 to 1550 °C. Therefore, a novel AlON phosphor [Mg_0.695Si_0.695Al_1.39]O_3.65N_0.35 has been synthesized after sintering at 1500 °C and it can be reasonably speculated that it was formed by replacing Al³⁺ ions in Al_2.78O_3.65N_0.35 by Mg²⁺ and Si⁴⁺ ions. The MSAON:Eu²⁺ phosphor shows high quantum yield, which provides the possibility of white light emission by introducing activator ions. The non-rare earth Mn²⁺ ion was introduced for adding the red emission region, which was attributed to the cheap price and emitting red light in the octahedral environment. As is known to all, the luminescence color of Mn²⁺ ion is affected by the crystal field strength. Mn²⁺ ion emits red emission when it lies in an octahedral lattice with a large crystal field and emits green emission when it lies in tetrahedron lattice with a low crystal field strength. Besides, the weaker absorption in the n-UV band is due to the d–d parity and spin forbidden transition.¹⁷^,¹⁸ Thus, Eu²⁺ ions as sensitizers are introduced into the MSAON host to enhance the red emission intensity for realizing white-light-emission based on energy transfer. Many similar successfully prepared phosphors are as follows: BaAl₁₁O₁₆N:Eu²⁺Mn²⁺,¹⁹ Ca₅(PO₄)₃(F_0.8Cl_0.2):Eu²⁺,Mn²⁺²⁰ and Lu₂MgAl₄SiO₁₂:Eu²⁺,Ce³⁺,Mn²⁺.19, 20, 21

In the study, the phosphors doped with Eu²⁺ and Eu²⁺/Mn²⁺ have been investigated in detail. The crystal structure is discussed. The energy transfer mechanism between Eu²⁺/Mn²⁺ was verified by photoluminescence spectra and decay curves. Moreover, quantum yield, thermal stability and encapsulation performance also confirm their potential in WLEDs applications.

Section snippets

Materials and preparation

Mg_0.695-x-y-zSi_0.695Al_1.39O_3.65N_0.35:xEu²⁺,yMn²⁺ (0 ≤ x ≤ 0.10, 0 ≤ y ≤ 0.10) phosphors were prepared by high-temperature solid-state reaction. The crude materials were MgCO₃ (Aladdin, 99.9%), SiO₂ (Aladdin, 99.9%), Al₂O₃ (Aladdin, 99.9%), AlN (Aladdin, 99.9%), Eu₂O₃ (Aladdin, 99.99%), and MnCO₃ (Aladdin, 99.99%). The reactants were weighed in stoichiometric proportions and mixed with 2 wt% of MgF₂ (AR) acting as a flux agent. Then, the mixture was ground in an agate mortar and then put into an

Crystal structure analysis

The XRD patterns of MSAON:xEu²⁺ (0 ≤ x ≤ 0.10) and MSAON:0.06Eu²⁺,yMn²⁺ (0.02 ≤ y ≤ 0.10) samples with the standard diffraction peaks of Al_2.78O_3.65N_0.35 (PDF #80–2173) are exhibited in Fig. 1(a, b). All the observed diffraction peaks of the samples can be index to cubic phase of Al_2.78O_3.65N_0.35 and no significant impurity phases are observed, which indicates the synthesis of target compounds doped with Eu²⁺ and Mn²⁺ ions, and the successful co-substitution of Mg²⁺-Si⁴⁺ for Al³⁺-Al³⁺. In

Conclusions

A novel nitrogen-oxide phosphor MSAON:Eu²⁺,Mn²⁺ with color-tunable properties was designed and prepared. The crystal structure, diffuse reflection, photoluminescence spectrum, energy transfer mechanism and application were investigated in detail. The crystal structure with Fd-3m (227) space group was determined. MSAON:xEu²⁺ phosphor shows a blue-broadband emission with a peak at 464 nm and a strong broadband excitation peaked at around 365 nm, which matches well with n-UV WLEDs. Meanwhile, the

References (34)

X. Zhang et al.
First-principles study of the electronic structure and optical properties of Eu²⁺–M (M = Mn²⁺, Mg²⁺, Li⁺) co-doped γ-AlON phosphor
Ceram Int
(2019)
H.L. Li et al.
Rapid synthesis of AlON powders by low temperature solid-state reaction
Ceram Int
(2019)
Q.Y. Chen et al.
A contrast of carbothermal reduction synthesis of MgAlON and AlON powders fortransparent ceramics
J Alloys Compd
(2019)
Y.Q. Zhang et al.
Photoluminescence properties of Eu²⁺–Mn²⁺ codoped Ca-a-SiAlON phosphors
J Lumin
(2012)
W.J. Park et al.
Synthesis and luminescent properties of Eu²⁺ doped nitrogen-rich Ca-a-SiAlON phosphor for white light-emitting diodes
Solid State Sci
(2010)
D.C. Huang et al.
Photoluminescence properties and thermal stability of Eu²⁺ and Mn²⁺ co-doped BaSi₃O₄N₂ Phosphors
J Alloys Compd
(2015)
L.J. Yin et al.
Luminescent properties of a novel Al₁₀O₃N₈:Eu²⁺ phosphor by a mechanochemical activation route
Opt Mater
(2015)
W.W. Hu et al.
Luminescence properties and energy transfer in Al₅O₆N:Ce³⁺, Tb³⁺ phosphors
J Lumin
(2014)
J.S. Huo et al.
Effective assembly of a novel aluminum-oxynitride BaAl₁₁O₁₆N activated by Eu²⁺ and Mn²⁺ via salt-flux assistance and its photophysical investigation
J Alloys Compd
(2019)
J.S. Mao et al.
Luminescence of halophosphate solid-solution Ca₅(PO₄)₃(F_0.8Cl_0.2):Eu²⁺,Mn²⁺ for WLED
J Rare Earths
(2018)

Z.Q. Ming et al.

Luminescence and energy transfer of color-tunable Lu₂MgAl₄SiO₁₂:Eu²⁺,Ce³⁺,Mn²⁺ phosphors

J Rare Earths

(2020)

F.P. Ruan et al.

Multichannel luminescence properties and ultrahigh-sensitive optical temperature sensing of mixed-valent Eu²⁺/Eu³⁺ co-activated Ca₈ZrMg(PO₄)₆(SiO₄) phosphors

J Alloys Compd

(2019)

K. Li et al.

Phase transition and multicolor luminescence of Eu²⁺/Mn²⁺-activated Ca₃(PO₄)₂ phosphors

Mater Res Bull

(2014)

S.H. Wang et al.

A novel red phosphor Ba₂La₄Y₄(SiO₄)₆O₂:Eu³⁺ with high quantum yield and thermal stability for warm white LEDs

J Alloys Compd

(2019)

R. Zhao et al.

Luminescent properties of blue long-lasting phosphorescence phosphors Sr₆Al₁₈Si₂O₃₇:Eu²⁺,RE³⁺

J Rare Earths

(2014)

F. Wang et al.

Tunable luminescence of Na₃YSi₃O₉:Ce³⁺, Mn²⁺ via efficient energy transfer for white LEDs

J Lumin

(2019)

Y.F. Liu et al.

An excellent cyan-emitting orthosilicate phosphor for NUV-pumped white LED application

J Mater Chem C

(2017)

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The Ca₉MgNa(PO₄)₇: Eu²⁺, Mn²⁺ (CMNPO: Eu²⁺, Mn²⁺) phosphors were successfully prepared via high-temperature solid-phase method. Under near ultraviolet light (n-UV) excitation, CMNPO: Eu²⁺, Mn²⁺ phosphor exhibits blue and red double emissions centered at 419 nm and 642 nm due to Eu²⁺: 5d → 4f transition and Mn²⁺: ⁴T₁(⁴G) → ⁶A₁(⁶S) transition, respectively, which match well with the chlorophyll a and b absorption spectrum required for plant growth. The energy transfer (ET) efficiency between Eu²⁺ and Mn²⁺ ions was analyzed and is as high as 90.0%. Besides, the luminescence mechanism and ET process of the phosphors were explained according to the simple energy level diagram of Eu²⁺ and Mn²⁺ ions. In addition, it was also found that the phosphor has good thermal stability (the luminescence intensity maintains 77.4% at 423 K). Finally, a LED device was packaged with the obtained phosphor Ca₉MgNa(PO₄)₇: 0.03Eu²⁺, 0.23Mn²⁺ and a commercial 365 nm n-UV chip, and the corresponding color rendering index R_a and the correlated color temperature (CCT) is 83.6 and 1842 K, respectively. The results show that the optimized phosphor has good application potential in plant cultivation LEDs.
Structure, luminescence and energy transfer of Eu2+/Mn2+ co-doped SrO-MgO-B<inf>2</inf>O<inf>3</inf> glass for full-color emitting WLEDs
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A series of Eu²⁺/Mn²⁺ co-doped SrO-MgO-B₂O₃ glasses have been synthesized via the conventional melt-quenching technique. The DSC curve, XRD, FT-IR and photoluminescence properties were investigated in detail. Continuous tunable emission from blue to warm white light can be achieved by varying the doping content of Mn²⁺. The energy transfer is taken place from the 4f⁶5d state of Eu²⁺ to the ⁴T₂ (G) state of Mn²⁺ and was confirmed to be dipole–dipole interaction in nature. Furthermore, the simply assembled WLED lamp exhibits white light near standard with color coordinates of (0.3345, 0.3091) and CCT of 5369 K under 20 mA current.
Strong energy transfer and color tunable emission in Eu2+ and Mn2+ co-doped Na<inf>2</inf>BaSr(PO<inf>4</inf>)<inf>2</inf> phosphor
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The new dual-emitting and color tunable single phase of Na₂BaSr(PO₄)₂:0.03Eu²⁺, xMn²⁺ (NBSP:0.03Eu²⁺, xMn²⁺) phosphor are successful prepared in this work. The phase purity and photoluminescence properties are investigated. Regarding to the coordination, valence and cation radius, the Eu²⁺ ions occupy the Sr2 and Sr3 site and Mn²⁺ ions occupy the Sr3 site. According to the photoluminescence (PL) spectra of NBSP:0.03Eu²⁺, xMn²⁺ (x = 0–0.09), the strong energy transfer (ET) between Eu²⁺ and Mn²⁺ exists in these phosphors. The strong ET efficiency from Eu²⁺ to Mn²⁺ is as high as 92%, while the ET mechanism of Eu²⁺ and Mn²⁺ is quadrupole-quadrupole interaction. Moreover, the CIE coordinate of Eu²⁺ and Mn²⁺ co-doped Na₂BaSr(PO₄)₂ phosphors can realize the color tunable emission from blue to cold white. The temperature dependent photoluminescence intensity of NBSP:0.03Eu²⁺, 0.05Mn²⁺ phosphor still keeps 75.8% of that initial intensity when the temperature is 150 °C. In summary, the NBSP:0.03Eu²⁺, xMn²⁺ phosphors have a promising application in white light LED.
Luminescent ionic lattice occupation and wide tunable emission spectra of La<inf>2</inf>MgZrO<inf>6</inf>:Bi3+,Eu3+ double perovskite phosphors for white light LED
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Citation Excerpt :
Color-coordinated phosphors have recently received extensive attention due to their application-potential in temperature sensors, plasma display panels, light-emitting diodes, and other fields.1–4 As per previous reports, the color tunning-emission of phosphors was often achieved by adjusting the energy transfer between the activator and the sensitizer,5,6 such as Y4GeO8:Bi3+,Eu3+,7 Y3MgAl3SiO12:Ce3+,Mn2+8 and Ca2GdTaO6:Bi3+,Mn4+.9 At the same time, the current commercial pc-WLED technology is based on the “blue LED chip + Y3Al5O12:Ce3+ (YAG:Ce) yellow phosphor” method with good thermal stability, but its red emission defect results in a low color rendering index and a high color temperature of the packaged LED.10
La₂Mg_1–x/2Zr_1–x/2O₆:xBi³⁺ (x = 0.01–0.035, abbreviated as LMZ:Bi³⁺) and La_2–yMg_0.99Zr_0.99O₆:0.02Bi³⁺,yEu³⁺ (y = 0.1–0.11, abbreviated as LMZ:Bi³⁺,Eu³⁺) double-perovskite phosphors were prepared through high-temperature solid-phase method. The emission spectrum of LMZ:xBi³⁺ (x = 0.01–0.035) phosphors excited at 353 nm is asymmetric in the range between 375 and 650 nm, showing strong green light. There are two luminescent centers of [Mg1/Zr2–O₆] and [Mg2/Zr1–O₆] for Bi³⁺ occupation, which were analyzed through different excitation wavelengths, Gaussian fitting peaks, fluorescence decay curves and Rietveld refinement of powder X-ray diffraction data. Through deep study of the luminescent lattices in the LMZ matrix, the green to blue tunning-emission is observed by different excitation wavelengths. In addition, red emission is obtained by co-doping Bi³⁺/Eu³⁺, and adjustable emission was investigated by changing the content of Eu³⁺ in the co-doped phosphor formulation, so it is converted from green emission to red emission. The above results demonstrate how to tune emission color by co-doping rare earth ions in the double perovskite phosphor, which is attractive for future applications.
Emission-tunable Ba<inf>2</inf>Y<inf>1–x</inf>Sc<inf>x</inf>NbO<inf>6</inf>:Bi3+ (0 ≤ x ≤ 1.0) phosphors for white LEDs
2022, Journal of Rare Earths
Here, we report a series of Bi³⁺-doped Ba₂Y_1–xSc_xNbO₆ (0 ≤ x ≤ 1.0 mol) phosphors by using the traditional high temperature solid-state reaction. To achieve the structural and photoluminescent (PL) information, several experimental characterizations and theoretical calculations were carried out, including X-ray diffraction (XRD), Rietveld refinement, UV-visible diffuse reflectance and PL spectra, temperature dependent PL spectra, and density functional theoretical (DFT) calculations. The XRD results show that the Bi³⁺-doped Ba₂Y_1–xSc_xNbO₆ samples belong to the double-perovskite phase with a cubic space group of Fm3̅m, and the diffraction positions shift toward high diffraction angle when the larger Y³⁺ ions are gradually replaced by the smaller Sc³⁺ ions. In addition, the refined XRD findings show that the Bi³⁺ ions tend to substitute the Y³⁺ and Sc³⁺ sites in the Bi³⁺-doped Ba₂Y_1–xSc_xNbO₆ (0 < x < 1.0 mol) solid solutions. The PL spectra show that the emission positions of the solid solution samples tune from 446 to 497 nm with the increase of Sc³⁺ content, which can be attributed to the modification of crystal field strength around Bi³⁺ ions. Moreover, there is energy transfer from the Ba₂YNbO₆ host to Bi³⁺ ions, which is dominated by a resonant type via a dipole-quadrupole (d-q) interaction. The Ba₂Y_0.6Sc_0.4NbO₆:0.02 molBi³⁺ shows the strongest PL intensity under 365 nm excitation, with the best quantum efficiency (QE) of 68%, and it keeps 60% of the room temperature emission intensity when the temperature increases to 150 °C, meaning that the Ba₂Y_0.6Sc_0.4NbO₆:Bi³⁺ features excellent thermal quenching of luminescence. By combining this optimal sample with a commercial red-emitting Sr₂Si₅N₈:Eu²⁺ phosphor, and a commercial 365 nm UV LED chip, a white LED device, with the color temperature (CT) of 3678 K, color rendering index (CRI) of 67.9, and CIE coordinates at (0.371, 0.376), is achieved.
Tuning structural and optical characteristics with Mn2+ introduced into ZnAl<inf>2</inf>O<inf>4</inf>:Cr3+ nanophosphors: Energy transfer process and cations rearrangement
2021, Journal of Luminescence
Cr³⁺/Mn²⁺ co-doped ZnAl₂O₄ (ZAO) phosphors were synthesized by using common sol-gel method. The crystallinity and particle morphology of the product samples were analyzed by using X-ray diffraction and scanning electron microscope. The atomic occupation was characterized by using X-ray photoelectron spectroscopy, indicating that the inversion defects were absent with Mn²⁺ entering the spinel lattices. The characteristic red quintuplets of Cr³⁺ were observed in singly doped ZAO phosphors, and became dual emissions at 685 nm and 690 nm with 1 nm of full width at half maximum in Mn²⁺/Cr³⁺ co-doped ZAO phosphors. The energy transfer from Mn²⁺ to Cr³⁺ was present with 96% of energy transfer efficiency. Mn²⁺ ions reduced the inversion defects and enhanced the electrons transition probability related to R line. The maximum enhancement factor of red emission was about 70. The CIE suggested that the co-doped samples exhibited yellow emissions with blue light (427 nm) excitation. ZAO:Mn²⁺,Cr³⁺ phosphors are proved to be promising candidates for red laser and white LED driving with green light.

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^☆: Foundation item: Project supported by the Zhejiang Natural Science Foundation of China (LZ20F050001), Zhejiang Provincial Natural Science Foundation of China (LY19E020005), and National Key R&D Program of China (2017YFB0403705).

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Emission tunable of Mg0.695Si0.695Al1.39O3.65N0.35:Eu2+,Mn2+ oxynitride phosphors via energy transfer for WLEDs☆

Abstract

Graphical abstract

Introduction

Section snippets

Materials and preparation

Crystal structure analysis

Conclusions

Ceram Int

Ceram Int

J Alloys Compd

J Lumin

Solid State Sci

J Alloys Compd

Opt Mater

J Lumin

J Alloys Compd

J Rare Earths

J Rare Earths

J Alloys Compd

Mater Res Bull

J Alloys Compd

J Rare Earths

J Lumin

An excellent cyan-emitting orthosilicate phosphor for NUV-pumped white LED application

J Mater Chem C

Emission tunable of Mg_0.695Si_0.695Al_1.39O_3.65N_0.35:Eu²⁺,Mn²⁺ oxynitride phosphors via energy transfer for WLEDs☆