光谱学与光谱分析, 2020, 40 (6): 1895, 网络出版: 2020-12-08  

(Ca1-xBax)2SiO4∶Eu荧光粉相变和光谱调控

Cation Substitution-Dependent Phase Transition and Color-Tunable Emission in (Ca1-xBax)2SiO4∶Eu Phosphor Series
作者单位
1 南昌大学材料科学与工程学院, 江西 南昌 330001
2 南昌大学江西省轻质高强结构材料重点实验室, 江西 南昌 330001
摘要
采用高温固相法在1 170 ℃还原气氛下保温3.5 h制备了(Ca1-xBax)1.95SiO4∶0.05Eu(x=0, 0.1, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0)系列新型荧光粉, 并研究了其基体晶相、 Eu离子价态、 光谱性能。 随着x值增大, 粉末物相组成发生如下改变: γ-Ca2SiO4(x=0)→T相和γ-Ca2SiO4混合物(0≤x<0.7)→T相(0.7≤x<0.9)→Ba2SiO4相(x≥0.9), 即(Ca1-xBax)2SiO4粉末只在富Ba端形成有限置换型固溶体, 即T相和Ba2SiO4相粉末。 点阵参数精确分析表明: 随着Ba离子增加, T相荧光粉(0.7≤x<0.9) 处于M1, M2, M5点位碱土离子配位数增大进而晶格参数增大较为明显, 而Ba2SiO4相荧光粉(x≥0.9)中碱土离子配位数无变化晶格参数变化也较小; Eu离子以取代碱土离子方式进入晶格, 对晶格影响较小。 T相和Ba2SiO4相荧光粉XPS全谱分析结果类似, 均出现Ba(3p3/2), Ba(3d3/2), Ba(3d5/2), O(1s), Eu(4d), Si(2p3/2)电子结合特征峰; 其O(1s)核心电子结合能精细谱也类似, 有2个光电子峰组成, 分别对应晶格氧、 间隙氧缺陷(Eu3+取代+2碱土离子造成); 进一步Eu(4d)高分辨XPS分析表明, 随着x值增大, T相粉末Eu2+/Eu3+比值增大(Eu离子形成+2可能性增大), 而Ba2SiO4相粉末Eu2+/Eu3+比值变化不明显。 在254和365 nm紫外激发下Ca1.95SiO4∶0.05Eu(γ-Ca2SiO4相荧光粉)可用作红色荧光粉, 而(Ca1-xBax)1.95SiO4∶0.05Eu(x≥0.7, 即T相(其绿光宽谱发射峰中心在455 nm附近)或Ba2SiO4相荧光粉(其绿光宽谱发射峰中心在510 nm附近))可用作绿色荧光粉; T相荧光粉绿光发射比Ba2SiO4相荧光粉绿光发射对应波长更短; 随着x值增加T相和Ba2SiO4相荧光粉发射光谱发生蓝移(即T相粉末中(Ca0.3Ba0.7)1.95SiO4∶0.05Eu绿光发射波长最长, Ba2SiO4相粉末中(Ca0.1Ba0.9)1.95SiO4∶0.05Eu 绿光发射波长最长); 随着x值增加, T相荧光粉亮度提高, 而Ba2SiO4相荧光粉亮度降低, 即(Ca0.1Ba0.9)1.95SiO4∶0.05Eu粉末的绿色荧光最亮(荧光寿命571.8 ns、 量子效率55%)。 由绿色荧光粉(x≥0.7)精细发射光谱可知: x值会影响Ba2SiO4相Eu2+占位倾向, x值越大Eu2+在Ba2SiO4相荧光粉中进入高配位点几率越小(x值小, Ca离子占据9配位点位, 有促进Eu离子倾向进入10配位作用), 但在T相中的x值作用则不明显。 由此可见: 改变固溶度(即控制x值), 可实现该系列荧光粉物相组成、 晶格参数、 离子价态、 荧光颜色及亮度的调控。
Abstract
(Ca1-xBax)1.95SiO4∶0.05Eu (x=0, 0.1, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) new phosphor series were prepared by high temperature solid-state reaction at 1 170 ℃ under a reduction atmosphere for 3.5 hours in this paper. The matrix crystal structure, Eu ion valence, photoluminescence spectra and fluorescence lifetime and quantum efficiency had been investigated. The matrix phase constituents change as γ-Ca2SiO4 (x=0)→T phase and γ-Ca2SiO4 mixture (0<x<0.7) →T phase (0.7≤x<0.9)→Ba2SiO4(0.9≤x≤1) as Ba ion content increasing. By XRD analysis, it is known that (Ca1-xBax)2SiO4 powders form solid solution phases at the Ba-rich end, which are T-phase and Ba2SiO4-phase. Precision measurement of lattice parameters had been also done to T-phase (0.7≤x<0.9) and Ba2SiO4 phase (x≥0.9). For the former phase powder, the lattice parameters would increase because coordinated numbers for M1, M2, M5 sites are increasing as Ba ion content increasing, While, change from the latter one’s lattice parameters would be neglecting. Moreover, Eu ions enter into the crystal lattice by substituting for alkaline earth ions, with a minor impact. The surveys of X-ray photoelectron spectroscopy (XPS) spectra are similar, which all show characteristic electron binding energy peaks of Ba(3p3/2), Ba(3d3/2), Ba(3d5/2), O(1s), Eu(4d) and Si(2p3/2). The high-resolution spectrum of O(1s) has two peaks, corresponding to lattice oxygen and interstitial oxygen defects (caused by Eu3+ substitution to alkaline earth ion+2), respectively. Moreover, the high-resolution XPS spectrums of the Eu(4d5/2) shows that the Eu2+/Eu3+ ratio would increase as the increasing of Ba ions in the T-phase powders, while the Eu2+/Eu3+ ratio of Ba2SiO4-phase powders is not obviously changed. Ultraviolet photoluminescence photographs show that Ca1.95SiO4∶0.05Eu (γ-Ca2SiO4 phase phosphors) could be used as red phosphors, while (Ca1-xBax)1.95SiO4∶0.05Eu (x≥0.7, T-phase (green emission centered at 455 nm) or Ba2SiO4-phase phosphors (green emission peak centered at 510 nm) could green phosphors. T-phase phosphors emission is blue shift comparing with Ba2SiO4 phase phosphor. Both T-phase and Ba2SiO4-phase phosphors are blue-shifted with the increase of x value. The brightest phosphor is (Ca0.1Ba0.9)1.95SiO4∶0.05Eu (fluorescence lifetime 571.8 ns, quantum efficiency 55%, which is the shortest lifetime and highest efficiency among the green phosphors). The high-resolution photoluminescence emission spectra of green phosphor (x≥0.7) show that that Eu2+ prefers more the site with 10 coordination than the site with 9 coordination as x value decreasing in Ba2SiO4-phase crystal (the Eu2+ activators with 10-coordination contribute more in green emission), but the site preference phenomenon is vague in the case of T-phase crystal. Overall, cation substitution (i. e. controlling the x value) should be a valid way to adjust the phase constituent, lattice, ion valence, photoluminescence CIE value and intensity for the phosphor.

汪雨, 罗岚, 郭锐, 孙传耀, 高明远. (Ca1-xBax)2SiO4∶Eu荧光粉相变和光谱调控[J]. 光谱学与光谱分析, 2020, 40(6): 1895. WANG Yu, LUO Lan, GUO Rui, SUN Chuan-yao, GAO Ming-yuan. Cation Substitution-Dependent Phase Transition and Color-Tunable Emission in (Ca1-xBax)2SiO4∶Eu Phosphor Series[J]. Spectroscopy and Spectral Analysis, 2020, 40(6): 1895.

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