【作者】 符义兵；

【导师】 施朝淑； 张国斌；

【作者基本信息】 中国科学技术大学 ， 核技术及应用， 2007， 博士

【摘要】 本论文由两部分组成。第一部分，也是论文的主要部分，研究了Pr³⁺，Mn²⁺共激活的几种铝酸盐和硼酸盐材料中的量子剪裁现象，着重讨论了LaMgB₅O₁₀：Pr³⁺，Mn²⁺中Pr³⁺→Mn²⁺能量传递过程。第二部分，研究了长余辉材料Sr₂MgSi₂O₇：Eu²⁺及Sr₂MgSi₂O₇：Eu²⁺，Dy³⁺的发光及余辉性能，重点讨论了Eu²⁺，Dy³⁺在Sr₂MgSi₂O₇：Eu²⁺，Dy³⁺长余辉发光过程中的作用。在第一部分中，首先回顾了可见光量子剪裁研究的现状及存在的问题，指出目前量子效率较高的材料如：LiGdF₄：Eu³⁺、LiGdF₄：Er³⁺，Tb³⁺等，都采用了氟化物作为基质材料，从而限制了它们的应用前景。为此，我们将研究氧化物量子剪裁材料，并选用“Pr³⁺，Mn²⁺”对作为激活离子。第三章研究了Pr³⁺激活的SrA₁₂O₁₉，SrB₄O₇，LaB₃O₆及LaMgB₅O₁₀材料的低温光谱性质。从发射谱上看，在这四种材料中都存在量子剪裁现象（光子级联发射）。从激发谱上看在这四种材料中Pr³⁺能够直接有效的吸收VUV光子的能量，而不需要来自基质的能量传递。另外在SrA₁₂O₁₉：Pr³⁺，LaB₃O₆：Pr³⁺及LaMgB₅O₁₀：Pr³⁺的激发谱上观测到了Pr³⁺宇称禁戒的³H₄→¹S₀跃迁，从而确定了在这三种材料中Pr³⁺-¹S₀能级分别位于最低的4f5d能级下2052cm^-1，1815cm^-1和1348cm^-1。随后，研究了Mn²⁺激活的SrAl₁₂O₁₉，SrB₄O₇，LaB₃O₆以及LaMgB₅O₁₀的光谱性质。在LaB₃O₆中，由于Mn²⁺难以取代La³⁺或B³⁺的格位，所以在LaB₃O₆：Mn²⁺中没有观测到Mn²⁺的发光。而另外三种材料都有来自Mn²⁺的绿光或红光发射。在SrAl₁₂O₁₉和SrB₄O₇中，由于Mn²⁺取代的是半径较大的阳离子Sr²⁺从而处在较弱的晶场中，所以在这两个材料中Mn²⁺的发光为波长较短的绿光（515nm左右）。而在LaMgB₅O₁₀中，Mn²⁺取代的是半径较小的Mg²⁺从而处在较强的晶场中，导致Mn²⁺的发光为615nm红光。测量了SrAl₁₂O₁₉：Mn²⁺，SrB₄O₇：Mn²⁺以及LaMgB₅O₁₀：Mn²⁺VUV-VIS区的激发光谱，指出在300-550nm范围内一些分立的激发峰来自Mn²⁺-3d⁵→3d⁵跃迁，而VUV区的两个激发带分别来自基质吸收和“Mn²⁺-O^2-”的电荷迁移态吸收。第五章研究了Pr³⁺，Mn²⁺共掺杂的SrAl₁₂O₁₉，SrB₄O₇以及LaMgB₅O₁₀中Pr³⁺→Mn²⁺能量传递。由于SrAl₁₂O₁₉：Pr³⁺的发射光谱和SrAl₁₂O₁₉：Mn²⁺的激发光谱上并没有光谱重叠存在，所以SrAl₁₂O₁₉：Pr³⁺，Mn²⁺中并没有能量传递发生。而SrB₄O₇：Pr³⁺和LaMgB₅O₁₀：Pr³⁺的发射光谱分别与SrB₄O₇：Mn²⁺和LaMgB₅O₁₀：Mn²⁺的激发光谱存在较多光谱重叠，使得在SrB₄O₇：Pr³⁺，Mn²⁺以及LaMgB₅O₁₀：Pr³⁺，Mn²⁺中Pr³⁺→Mn²⁺的能量传递成为可能。通过Pr³⁺，Mn²⁺双掺样品的发射、激发光谱以及比较Pr³⁺单掺和Pr³⁺，Mn²⁺双掺样品中Pr³⁺-¹S₀发射的衰减时间，证实了上述能量传递过程。这种能量传递转化了部分Pr³⁺紫光或紫外光为Mn²⁺的绿光或红光发射，提高了量子剪裁过程中可见光发射的比例。以LaMgB₅O₁₀：Pr³⁺，Mn²⁺为例研究了LaMgB₅O₁₀中Pr³⁺→Mn²⁺能量传递的类型及途径。结果表明共振能量传递在材料中起主要作用。计算和讨论了LaMgB₅O₁₀：Pr³⁺，Mn²⁺中共振能量传递的临界传递距离，发现对于电偶极-电偶极相互作用，临界距离R_C^dd=4.78（?）；而电偶极-电四极相互作用，临界距离R_C^dq=9.46（?）；若是交换相互作用，临界传递距离R_C^ex也只有几个埃，都小于最大掺杂浓度下样品中Pr³⁺和Mn²⁺间的平均距离R_Pr-Mn～17（?）(Pr³⁺，Mn²⁺在样品中任意分布)。由于Pr³⁺，Mn²⁺离子半径分别小于和大于所替换的阳离子半径，所以我们认为：Pr³⁺，Mn²⁺在替换晶格阳离子的过程中可能成为近邻，从而降低系统的能量，这就使得LaMgB₅O₁₀：Pr³⁺，Mn²⁺中Pr³⁺→Mn²⁺能量传递的产生有了合理的解释。在第二部分中，研究了长余辉材料Sr₂MgSi₂O₇：Eu²⁺和Sr₂MgSi₂O₇：Eu²⁺，Dy³⁺的光谱性质和余辉性能。实验结果指出这两种长余辉材料的余辉发光主要来Eu²⁺-4f⁶5d→4f⁷允许跃迁产生的465nm蓝光。通过余辉光谱以及余辉衰减曲线的测量发现，Sr₂MgSi₂O₇：Eu²⁺，Dy³⁺余辉性能远优于Sr₂MgSi₂O₇：Eu²⁺。两种长余辉材料热释光曲线的拟合结果显示，这是因为Dy³⁺的加入在材料中产生了深度合适，浓度较高的陷阱能级所致。我们在真空紫外激发下Sr₂MgSi₂O₇：Eu²⁺，Dy³⁺的发射光谱上，同时测到了Eu²⁺和Dy³⁺的发光。并结合Sr₂MgSi₂O₇：Eu²⁺具有余辉性能的事实，说明Eu²⁺和Dy³⁺都既是陷阱也是发光中心。只不过UV激发下在Sr₂MgSi₂O₇：Eu²⁺，Dy³⁺中突显了Eu²⁺作为发光中心和Dy³⁺作为陷阱的作用。通过Sr₂MgSi₂O₇：Eu²⁺，Dy³⁺中余辉机理的讨论，认为Dy³⁺在这种长余辉材料中作为电子陷阱而不是目前普遍认为的空穴陷阱，而Eu²⁺可能是起空穴陷阱的作用。更多还原

【Abstract】 This dissertation included two parts. In the first part, we dealt with quantum cutting process in Pr³⁺, Mn²⁺ co-doped SrAl₁₂O₁₉, SrB₄O₇ and LaMgB₅O₁₀ systems. Main study was focused on the energy transfer process in LaMgB₅O₁₀: Pr³⁺,Mn²⁺. In the second part, the spectra and afterglow properties of long afterglow phosphor Sr₂MgSi₂O₇:Eu²⁺and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were investigated. Emphasis was made on the analyses of the roles of Eu²⁺ and Dy³⁺ in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺.In part one, firstly, we reviewed the present research states and remain problems in visible quantum cutting phosphors. In view of the fact that almost all the known quantum cutters with high efficiency are fluorides, like LiGdF4:Eu³⁺、LiGdF4:Er³⁺,Tb³⁺.While the practical phosphors are oxides, we decided to search for oxide based visible quantum cutters, and select "Pr³⁺Mn²⁺" as the prospective activaters.In chapter three, the low temperature spectra properties of Pr³⁺ doped SrA₁₂O₁₉, SrB₄O₇, LaB₃O₆ and LaMgB₅O₁₀ were investigated by synchrotron radiation VUV light. Under VUV excitation, photon cascade emission was found in these phosphors. From the excitation spectra study, we conculded that the excitation energy can be efficiently absorbed by Pr³⁺-4f5d levels directly, but the host absorption wasn’t very efficient. In the excitation spectra of SrA₁₂O₁₉:Pr³⁺, LaB₃O₆:Pr³⁺ and LaMgB₅O₁₀:Pr³⁺, along with the 4f5d absorption bands, a weak peak due to ³H₄→¹S₀ transition also was detected. From the position of ³H₄→¹S₀ transition and the absorption edge of 4f5d band, the position of Pr³⁺-¹S₀ state was determined at 2052 cm^-1, 1815 cm^-1 and 1348 cm^-1 below the lowest 4f5d state, respectively.In the following chapter, the spectra properties of Mn²⁺ doped SrAl₁₂O₁₉, SrB₄O₇, LaB₃O₆ and LaMgB₅O₁₀ were studied. In LaB₃O₆ matrix, due to the difficulty to substitute La³⁺ or B³⁺ by Mn²⁺, No emission from Mn²⁺ was found. Yet the other three phosphors showed efficient Mn²⁺ emission. In SrAl₁₂O₁₉: Mn²⁺ and SrB₄O₇: Mn²⁺, because Mn²⁺ substituted the Sr²⁺ with large ion radii which results in a weak crystal field, Mn²⁺ green emission （about 515 nm） was detected. While the emission of LaMgB₅O₁₀: Mn²⁺ was red, owing to the fact that the small ion radii site of Mg²⁺ was replaced by Mn²⁺. In the excitation spectra of SrAl₁₂O₁₉:Mn²⁺, SrB₄O₇:Mn²⁺ and LaMgB₅O₁₀: Mn²⁺, the peaks in the range of 300-550 nm were assigned to the transition of Mn²⁺-3d⁵→3d⁵, and the two bands in VUV range were attributed to host absorption and the absorption of "Mn²⁺-O^2- charge transfer states, respectively.Chapter five dealt with the Pr³⁺→Mn²⁺ energy transfer in Pr³⁺, Mn²⁺ co-doped SrAl₁₂O₁₉, SrB₄O₇ and LaMgB₅O₁₀. There wasn’t any spectra overlap between the emission spectra of SrAl₁₂O₁₉:Pr³⁺ and excitation spectra of SrAl₁₂O₁₉:Mn²⁺. So, energy transfer didn’t occur in SrAl₁₂O₁₉:Pr³⁺,Mn²⁺. While in the excitation spectra of SrB₄O₇:Mn²⁺ and LaMgB₅O₁₀:Mn²⁺, the ⁶A_1g→⁴E_g-⁴A_1g excitation band of Mn²⁺ had considerable spectra overlap with the Pr³⁺-¹S₀→¹I₆ emission in SrB₄O₇:Pr³⁺ and LaMgB₅O₁₀:Pr³⁺, which was favorable for energy transfer from Pr³⁺ to Mn²⁺ in Pr³⁺,Mn²⁺ co-doped sample. Such energy transfer was confirmed in SrB₄O₇: Pr³⁺,Mn²⁺ and LaMgB₅O₁₀:Pr³⁺,Mn²⁺, from the emission and excitation spectra study of the co-doped samples as well as comparing the decay curves of ¹S₀→¹I₆ transition of Pr³⁺ between Pr³⁺ singly doped and Pr³⁺,Mn²⁺ co-doped sample. The energy transfer processes converted the violet or UV emissions of Pr³⁺ into green or red emission of Mn²⁺, improved the ratio of visible emission in quantum cutting process.The Pr³⁺→Mn²⁺ energy transfer type and pathway were investigated in LaMgB₅O₁₀:Pr³⁺,Mn²⁺. The analyses showed that the energy transfer pathway was of resonant energy transfer. The critical distance of resonant energy transfer in LaMgB₅O₁₀:Pr³⁺,Mn²⁺ was calculated. As for electric dipole-dipole interaction and dipole-quadrupole interaction, the critical distance R_C was 4.78 （A|°） and 9.46（A|°）, respectively. For exchanged interaction, the critical distance also was several angstroms. All the values were less than the mean distance between Pr³⁺ and Mn²⁺ in the highest concentration doped sample (R_Pr-Mn～17 （A|°）), considering a random distribution of Pr³⁺ and Mn²⁺ in LaMgB₅O₁₀ matrix. Because the ion radii of Pr³⁺ and Mn²⁺ was lager and less than the ion radii of the cations in host matrix replaced by them, respectively. The replacement would lead to the formation of some near neighboring Pr-Mn clusters in the LaMgB₅O₁₀ host to reduce the system energy. And the short distance （less than R_C） between Pr³⁺ and Mn²⁺ can account for the occurrence of Pr³⁺→Mn²⁺ energy transfer in LaMgB₅O₁₀:Pr³⁺,Mn²⁺.In part two, the spectra and afterglow properties of long afterglow phosphors Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were investigated. The results showed that the afterglow luminescence of the two phosphors originates from the 465nm blue emission of Eu²⁺-4f⁶5d→4f⁷ allowed transition. The afterglow properties of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were better than that of Sr₂MgSi₂O₇:Eu²⁺, by the detection of afterglow spectra and the afterglow decay curves. The fitting results of the thermoluminescence curves of the two phosphors showed that, the defect levels arose from Dy³⁺ in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ had appropriate depth and high concentration, which resulted in the longer afterglow time in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ than that in Sr₂MgSi₂O₇:Eu²⁺.In the emission spectra of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ excited by VUV light, the Dy³⁺ emissions were detected along with the emission of Eu²⁺. Considering the long afterglow properties of Sr₂MgSi₂O₇:Eu²⁺, we can draw the conclusion that Eu²⁺ and Dy³⁺ both have duple roles, acting as not only the luminescence centers, but also trap centers. By analyzing the dynamics of the afterglow luminescence in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺, it was found that the Dy³⁺ acts as electron traps rather than hole traps which is accepted by many researchers, while the Eu²⁺ plays the role of hole traps.更多还原