Na1-xMxCaEu(WO4)3 (M=Li, K)红色荧光粉的微观结构与热猝灭特性研究

doi:10.15541/jim20210426

摘要/Abstract

摘要：

红色荧光粉对改善白光LED(w-LEDs)发光性能具有至关重要的作用。为制备与商用LED芯片相符的、高效和稳定性好的红色荧光粉, 本研究采用传统高温固相法合成了系列四方白钨矿结构的Na_1-_xM_xCaEu(WO₄)₃ (M= Li, K)红色荧光粉, 并系统研究了Li⁺和K⁺的掺杂对NaCaEu(WO₄)₃荧光粉晶体结构、发光性能以及热猝灭特性的影响。Rietveld精修结果显示, 掺杂Li⁺和K⁺没有改变NaCaEu(WO₄)₃基质的四方白钨矿结构, 而是形成了固溶体, 并且导致晶格常数呈现规律性的变化。光致发光光谱表明, 在近紫外光395 nm激发下, 荧光粉呈现典型的红色发射, 其最强发射峰位于617 nm处, 对应于Eu³⁺离子的⁵D₀→⁷F₂跃迁, 这表明Eu³⁺处于非对称中心格位。更值得注意的是掺杂Li⁺和K⁺有效改善了NaCaEu(WO₄)₃荧光粉的发光强度, 当Li⁺和K⁺的掺杂浓度(物质的量分数)分别为100%和30%时, 荧光粉的发光强度和色纯度达到最佳。此外, 还对Na_1-_xM_xCaEu(WO₄)₃ (M=Li, K)荧光粉的热猝灭特性机理进行了研究。结果显示, 掺杂Li⁺和K⁺荧光粉均表现出卓越的热猝灭特性, 其中当Li⁺掺杂浓度(物质的量)为100%时, LiCaEu(WO₄)₃荧光粉的热猝灭特性最佳。以上研究结果均表明Na_1-_xM_xCaEu(WO₄)₃ (M= Li, K)红色荧光粉在大功率近紫外激发的白光发光二极管中具有潜在的应用价值。

关键词: 荧光粉, 白钨矿结构, 热猝灭特性, 光致发光特性

Abstract:

Red phosphors play a vital role in improving the photoluminescence properties of white LEDs (w-LEDs). In order to prepare high efficiency and stability red phosphor for commercial LED chips, a series of tetragonal scheelite structure Na_1-_xM_xCaEu(WO₄)₃ (M=Li, K) red phosphors were synthesized by a solid state reaction method. The effect of Li⁺ and K⁺ doping on the crystal structure, photoluminescence properties and thermal quenching characteristics of NaCaEu(WO₄)₃ phosphor were investigated systematically. Rietveld refinement results show that the doping of Li⁺ and K⁺ exerts change on the tetragonal scheelite structure of the NaCaEu(WO₄)₃ host, but forms the solid solution, and results in the regular change in the lattice constant. The photoluminescence spectra show that under the excitation of near ultraviolet light at 395 nm, the phosphors exhibit a typical red emission, with the strongest emission peak at 617 nm, corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ ion, which indicates that Eu³⁺ is situated in non-central symmetric lattices in NaCaEu(WO₄)₃ host. It is noteworthy that the doping of Li⁺ and K⁺ effectively improves the emission intensity of the NaCaEu(WO₄)₃ phosphor. When the doping concentration (molar percent) of Li⁺ and K⁺ is 100% and 30%, respectively, both the emission intensity and the color purity realize optimum. In addition, thermal stability and thermal quenching characteristics of Na_1-_xM_xCaEu(WO₄)₃ (M=Li, K) phosphors were studied. The results show that both Li⁺ and K⁺ doped phosphors display excellent thermal quenching, and when the Li⁺ doping concentration (molar percent) is 100%, LiCaEu(WO₄)₃ phosphor processes the best thermal quenching. All results demonstrate that Na_1-_xM_xCaEu(WO₄)₃ (M= Li, K) red phosphors can be applied to high-power NUV (Near ultraviolet) excited white light emitting diodes potentially.

Key words: phosphor, scheelite structure, thermal quenching characteristics, photoluminescence property

中图分类号:

TQ174

关旭峰, 李桂芳, 卫云鸽. Na_1-_xM_xCaEu(WO₄)₃ (M=Li, K)红色荧光粉的微观结构与热猝灭特性研究[J]. 无机材料学报, 2022, 37(6): 676-682.

GUAN Xufeng, LI Guifang, WEI Yunge. Microstructure and Thermal Quenching Characteristics of Na_1-_xM_xCaEu(WO₄)₃ (M=Li, K) Red Phosphor[J]. Journal of Inorganic Materials, 2022, 37(6): 676-682.

图/表 9

图1 荧光粉的XRD谱图

Fig. 1 XRD patterns of phosphors (a) Na1-xLixCaEu(WO4)3; (b) Na1-xKxCaEu(WO4)3

图2 荧光粉的XRD Rietveld精修谱图

Fig. 2 Rietveld refinement XRD patterns of phosphors (a) LiCaEu(WO4)3; (b) NaCaEu(WO4)3; (c) KCaEu(WO4)3

表1 LiCaEu(WO4)3、NaCaEu(WO4)3和KCaEu(WO4)3荧光粉的Rietveld精修结构参数

Table 1 Structure parameters of LiCaEu(WO4)3, NaCaEu(WO4)3 and KCaEu(WO4)3

Materials	Crystal system	Space group	a=b/nm	c/nm	V/nm³	α=β=γ	R_wp/%	R/%_p	χ²
LiCaEu(WO₄)₃	Tetragonal	I4₁/a	0.5230570(26)	1.1319686(43)	0.309694(8)	90°	8.61	7.66	2.438
NaCaEu(WO₄)₃	Tetragonal	I4₁/a	0.5255477(32)	1.1393990(48)	0.314702(5)	90°	7.68	5.95	1.468
KCaEu(WO₄)₃	Tetragonal	I4₁/a	0.5273337(35)	1.1479226(52)	0.319357(6)	90°	7.94	6.17	1.315

图3 617 nm监测下LiCaEu(WO4)3、NaCaEu(WO4)3和KCaEu(WO4)3荧光粉的激发光谱图

Fig. 3 Excitation spectra of LiCaEu(WO4)3, NaCaEu(WO4)3 and KCaEu(WO4)3 phosphors monitored at 617 nm Colourful figures are available on website

图4 荧光粉的发射光谱和荧光粉发光强度对比图

Fig. 4 Emission spectra of phosphors and intensity contrast diagram of phosphors (a) Emission spectra of Na1-xLixCaEu(WO4)3; (b) Emission spectra of Na1-xKxCaEu(WO4)3; (c) Intensity contrast diagram of NaCaEu(WO4)3, Na0.7K0.3CaEu(WO4)3 and LiCaEu(WO4)3 phosphors Colorful figures are available on website

表2 NaCaEu(WO4)3、Na0.7K0.3CaEu(WO4)3和LiCaEu(WO4)3荧光粉色坐标和色纯度

Table 2 CIE chromaticity coordinates and color purities of NaCaEu(WO4)3, Na0.7K0.3CaEu(WO4)3 and LiCaEu(WO4)3 phosphors

Material	CIE chromaticity coordinate		Color purity/%
Material	x	y	Color purity/%
NaCaEu(WO₄)₃	0.6580	0.341	96.07
Na_0.7K_0.3CaEu(WO₄)₃	0.661	0.338	96.83
LiCaEu(WO₄)₃	0.665	0.334	97.87

图5 NaCaEu(WO4)3、Na0.7K0.3CaEu(WO4)3和LiCaEu(WO4)3 荧光粉的色坐标图

Fig. 5 CIE chromaticity diagram of NaCaEu(WO4)3, Na0.7K0.3CaEu(WO4)3 and LiCaEu(WO4)3 phosphors

图6 NaCaEu(WO4)3、Na0.7K0.3CaEu(WO4)3和LiCaEu(WO4)3荧光粉荧光寿命衰减曲线(λex=395 nm, λem=617 nm)

Fig. 6 Decay curves of NaCaEu(WO4)3, Na0.7K0.3CaEu(WO4)3 and LiCaEu(WO4)3 phosphors (λex=395 nm, λem=617 nm)

图7 不同温度下荧光粉的发射光谱图(λex=395 nm)(a~c)、ln(I0/IT-1)与1/(kT)的关系曲线(d)和热猝灭过程的能级位形坐标图(e)

Fig. 7 Emission spectra of phosphors at different temperatures (λex=395 nm) (a-c), plot of ln(I0/IT-1) versus 1/(kT) (d) and schematic illustration of a configuration coordinate diagram of the thermal quenching process (e) (a) NaCaEu(WO4)3; (b) Na0.7K0.3CaEu(WO4)3; (c) LiCaEu(WO4)3

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Na_1-_xM_xCaEu(WO₄)₃ (M=Li, K)红色荧光粉的微观结构与热猝灭特性研究

Microstructure and Thermal Quenching Characteristics of Na_1-_xM_xCaEu(WO₄)₃ (M=Li, K) Red Phosphor

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