Emission tunable of Mg0.695Si0.695Al1.39O3.65N0.35:Eu2+,Mn2+ oxynitride phosphors via energy transfer for 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 Al2.78O3.65N0.35 phosphors. It has been reported that a novel AlON polymorph of Mg1.25Si1.25Al2.5O3N3 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 [Mg0.695Si0.695Al1.39]O3.65N0.35 has been synthesized after sintering at 1500 °C and it can be reasonably speculated that it was formed by replacing Al3+ ions in Al2.78O3.65N0.35 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(F0.8Cl0.2):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
Mg0.695-x-y-zSi0.695Al1.39O3.65N0.35: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 Al2.78O3.65N0.35 (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 Al2.78O3.65N0.35 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
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2023, Journal of Rare EarthsCitation 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
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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).