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复相硅酸盐荧光粉的设计、合成及其稀土离子的自还原发光机理
中文摘要

硅酸盐荧光粉因其原料易得、价格便宜、稳定性好、有丰富多样的晶体结构等优点,在荧光粉领域受到广泛地关注与研究。本论文围绕硅酸盐荧光粉的设计、合成和掺杂的稀土离子自还原发光机理进行研究,制备了一系列基于碱土硅酸盐基质的荧光粉。 1.采用高温固相法制备了一系列Eu/Tm/Sm/Yb单掺杂的BaZnSiO₄荧光粉并讨论了稀土离子自还原发光的机理。详细地解释了Eu/Tm/Yb掺杂的BaZnSiO₄样品具有自还原发光现象,而Sm掺杂的样品没有自还原发光。对比空气中合成Eu/Tm/Yb掺杂的BaZnSiO₄荧光粉样品与还原气氛条件下合成样品的光谱数据,计算得到三种离子的自还原百分数分别为21%,15%,35%;通过电离能、电势、电负性,离子半径和晶体结构等分析了自还原程度不同的内在原因。在近紫外激发下,空气中合成的BaZnSiO₄:Eu〓和BaZnSiO₄:Tm〓荧光粉,都在500 am处有一个宽的发射带,这表明它们在紫外LED芯片激发方面具有潜在应用价值。在空气中成功合成BaZnSiO₄:RE(RE=Eu,Tm,Sm,Yb)荧光粉为获得新型正硅酸盐基质材料提供了一种新的途径。 2.在空气中,采用高温固相法制备了一系列复相荧光粉(1-x)BaMSiO₄·xBa₂MSi₂O₇:Eu〓(M=Zn,Mg)。分析了基质物相组成对低价Eu²⁺离子光谱的影响。实验结果表明,Eu³⁺离子在四种纯硅酸盐基质BaMSiO₄、Ba₂MSi₂O₇(M=Zn,Mg)中的自还原率并不是最高的,当复相基质中的两种物相约为1:1时,Eu³⁺离子可以达到最大自还原率。该现象的产生机理由缺陷理论进行了解释,基质两相间的异质结效应促进了自还原过程。 3.采用高温固相法制备了Eu、Ce共掺的白光发射复相(1-m)BaZnSiO₄·mBa₂ZnSi₂O₇荧光粉。调节复相荧光粉的物相比以及Ce³⁺的掺杂比例,能够实现可控调节荧光粉的发光,并讨论了Ce³⁺-Eu〓之间的能量传递过程与机理。 4.使用高温固相法制备了光谱可精细调控的蓝光发射Ca〓Sr〓B〓SiO〓:Ce〓,Li〓固溶体荧光粉。通过Ca₂SiO₄,Sr₂SO₄, Ba₂SiO₄荧光粉的实验光谱数据计算得到5d能级的晶体场分裂能和质心位移的近似值。随着掺杂离子半径的增加,所合成的Ca〓Sr〓Ba〓SiO₄:Ce³⁺,Li⁺固溶体荧光粉随着基质阳离子半径的增大,先从417 nm(Ca₂SiO₄)红移至438 nm(Sr₀.₃Ca₁.₆SiO₄),最后蓝移到401 nm(Ba₂SiO₄)。 5.采用高温固相法制备了Ce³⁺、Tb³⁺、Eu³⁺三掺杂硅酸盐固溶体荧光粉Sr〓Ca₂SiO₄。在基质Sr含量为65%-90%,稀土离子掺杂量分别为0.6%Ce³⁺、0.15%Tb³⁺、0.8%Eu³⁺时,该固溶体荧光粉能实现全光谱发射,其发射带与太阳光的发射十分吻合。该荧光粉可用于全光谱LEDs照明以及植物生长灯。 关键词:硅酸盐荧光粉,自还原,复相,全光谱发射,发光机理

英文摘要

The silicate phosphor has been widely studied in the field of phosphor because of easy availability of raw materials, the low manufacturing cost, chemical and thermal stability as well as many kinds of crystal structures. This work investigated the synthesis method and luminescence mechanism of silicate phosphors and prepared a series of phosphors based on alkaline earth silicates. 1.A series of Eu/Tm/Sm/Yb doped BaZnSiO₄ phosphors were prepared by high temperature solid-state method and the mechanism of self-reduction was discussed. Self-reduction phenomenon were observed in the samples of Eu/Tm/Yb-doped BaZnSiO₄ but have not observed in Sm-doped samples. Compared with RA condition, the ca. percent of the reductive concentration of Eu/Tm/Yb in the phosphors BaZnSiO₄ prepared in oxidizing atmosphere (OA) condition are 21%, 15% and 35%, respectively. Self-reduction ratio of rare earth ions in BaZnSiO₄ have been explained by ionization energy, potential, electronegativity, radii of ions and crystal structure. It was found that both BaZnSiO₄:Eu〓 and BaZnSiO₄:Tm〓 prepared in air shown greatly broad band emission peak at 500 nm under the excitation of ultraviolet (UV), which indicated they are potential phosphors for UV-based LED. The factors related to self-reduction degree have been also discussed. The successful synthesis of BaZnSiO₄:RE〓 (RE = Eu, Tm, Sm, Yb) phosphors in air provides a new route to obtain other novel orthosilicate-based materials. 2.We synthesized a series of (1-x)BaMSiO₄:xBa₂MSi₂O₇:Eu〓 (M = Zn, Mg) diphase phosphors by a high temperature solid-state reaction in air condition. Then we analyzed the change of luminescence property of low-valence Eu²⁺ related to the phase transform from BaMSiO₄ to Ba₂MSi₂O₇. These results show that when the four compounds are pure phases respectively, the self-reduction ability of Eu³⁺ is not the best. When two phases are in a proper ratio in the matrix, Eu³⁺ ions will get the highest reduction ability. This phenomenon was explained by the defect theory, and the heterostructure between the two matrix phases BaMSiO₄ and Ba₂MSi₂O₇ improves the self-reduction process. 3.Eu, Ce co-doped BaZnSiO₄·Ba₂MSi₂O₇ diphase phosphors with white emission were prepared by a high temperature solid-state reaction. Controlling the phase ratio in diphase phosphors and Ce³⁺ doping can adjust the luminescence property, and we discussed the energy transfer process and mechanism between Ce³⁺ and Eu〓 ions. 4.Fine controllable blue emission Ca〓Sr〓Ba〓SiO〓:Ce³⁺,Li⁺ solid solution phosphors were synthesized by a high temperature solid-state reaction. The approximation of the crystal field splitting and the centroid shift of 5d energy level were obtained from the spectrum for Ca₂SiO₄, Sr₂SiO₄ and Ba₂SiO₄ phosphors. With the increase of the doped ion radius, the emission peak wavelength red shift firstly from 417 nm of Ca₂SiO₄ to 438 nm of Sr₀.₃Ca₁.₆SiO₄ then blue shift to 401 nm of Ba₂SiO₄. 5.A series of solid solution phosphors Sr〓Ca〓SiO₄ codoped with Ce³⁺, Tb³⁺, Eu³⁺ were synthesized by traditional high temperature solid-state reaction. Within a certain Sr/Ca ratio and rare-earth ion doping amount, the solid-solution phosphor can realize full spectra emission, and the emission band is close to the sunlight emission. This phosphor has a potential application value for white phosphor for LED-based UV-chip using in illumination and plant growth light. Key Words: silicate phosphors, self-reduction, diphase, full spectra emission, luminescence mechanism

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