(Sr1-xMex)2SiO4:Eu荧光粉光谱调控机制

Luminescent spetra regulation mechnism of (Sr1-xMex)2SiO4:Eu

摘要:

采用高温固相法制备(Sr1-xMex)1.95SiO4:0.05Eu系列荧光粉，研究不同大(Ba2+)、小(Mg2+)半径离子基体固溶对其物相、发光中心配位结构、Eu离子价态的影响，探究其光谱精细调控机制。Sr2SiO4粉末中随着温度升高α-Sr2SiO4相增加、β-Sr2SiO4相减少；Mg2+ (小半径离子)掺杂可以提高α-Sr2SiO4相稳定性，但容易出现Mg2SiO4，粉末中始终为混合物；Ba2+ (大半径离子) 掺杂可以提高α-Sr2SiO4相稳定性，粉体发生β-Sr2SiO4+α-Sr2SiO4→α-Sr2SiO4→α-Sr2SiO4+Ba2SiO4→Ba2SiO4转变，且β-Sr2SiO4、α-Sr2SiO4、Ba2SiO4的顺序其Si–O–Me(I)–O–Me(II)链逐渐由锯齿状变为平直状、Me-O键长拉长。Eu离子激活的β-Sr2SiO4、α-Sr2SiO4、Ba2SiO4粉体在254nm(365nm) 激发下有明亮的绿色荧光发射（且依序强度增强、光谱整体略微蓝移）和微弱的红光发射；当光学基体发生β-Sr2SiO4→α-Sr2SiO4转变时，发射光谱中Eu2+(I)蓝移Eu2+(II)红移（Si–O–Sr(I)–O–Sr(II)由锯齿形链成为平链，且Sr-O键拉长），发生α-Sr2SiO4→Ba2SiO4转变则Eu2+(I)、Eu2+(II)均发生蓝移（仅发生Me-O键拉长）；三种粉体热释光谱中均存在Eu2+和Eu3+缺陷能级，且Eu2+缺陷浓度更高。Eu3d的精细x射线光电子谱表明随着β-Sr2SiO4→α-Sr2SiO4→Ba2SiO4转变其Eu离子以Eu2+存在的可能性增大，对应的电子顺磁共振也证实这一结果。由此可见，采用Ba2+离子固溶掺杂Sr2SiO4，可在一定浓度范围得到单相粉末，实现光学基体的β-Sr2SiO4→α-Sr2SiO4→Ba2SiO4相变，调控Si–O–Me(I)–O–Me(II)链型及Me-O键长，调节Eu离子价态和配位场，进而实现其绿色荧光粉荧光强度、发射波段精确调控。

Abstract:

The (Sr1-xMex)1.95SiO4：0.05Eu phosphor powders were synthesized by high temperature solid-state reaction. The effects of solid solution of different large (Ba2+) and small (Mg2+) ionic on the phase, the coordination crystal structure and the valence state of Eu ions were investigated firsly, and then regulation mechanism in the luminscent spectra was disccused. With increasing temperature, α-Sr2SiO4 increases and β-Sr2SiO4 phase decreases in Sr2SiO4 powder. Mg2+ ion dopant would increase the stability of α-Sr2SiO4 phase. Ba2+ ion dopant would lead the phase tranformation as β-Sr2SiO4+α-Sr2SiO4→α-Sr2SiO4→α-Sr2SiO4+Ba2SiO4→Ba2SiO4, in the sequence as β-Sr2SiO4, α-Sr2SiO4, Ba2SiO4, the Si–O–Me(I)–O–Me(II) chain changes from zigzag to straight chain, and the Me-O length increases. Under the excitation of 254nm (365nm), Eu-activated β-Sr2SiO4, α-Sr2SiO4, and Ba2SiO4 powders have bright green fluorescence emission (in the same sequence, the intensity increases and the overall spectrum is slightly blue shifted) and weak red light emission. For β-Sr2SiO4 →α-Sr2SiO4, Eu (I) emission peak is blue-shifted while the one of Eu (II) is red-shifted (Si–O–Me(I)–O–Me(II) chain changes from zigzag to straight, Me-O length increases). For α -Sr2SiO4 →Ba2SiO4, both emission peaks of Eu (I) and Eu (II) are blue-shifted (Me-O bond is enlonged). In the thermoluminescence spectra, there exit Eu2+ and Eu3+ defect energy levels in all these phosphors, and Eu2+ concentration looks larger. The high resolution XPS spectrum of Eu3d indicates that there are higher possibilities for Eu2+ in the sequence as β-Sr2SiO4 → α-Sr2SiO4 → Ba2SiO4, which is confirmed by Eu ion ESR spetra. By Ba2+ ions solid solution into Sr2SiO4 crystal, phase transforamtion as β-Sr2SiO4 → α-Sr2SiO4 → Ba2SiO4 would occurs, which would means the adjustmens in Si–O–Me(I)–O–Me(II) chain type and Me-O bond length. These would lead to the regulation in the coordination environment and valence state (Eu2+/ Eu3+ ratio) of Eu ion, and result to regular in emission wavelength and intensity.