【作者】 王义飞；

【导师】 徐鑫；

【作者基本信息】 中国科学技术大学 ， 材料学， 2011， 博士

【摘要】 随着照明、显示技术的迅速发展,作为大部分照明、显示器件关键之一的荧光材料科学和技术又步入一个新的活跃期。新型器件对荧光粉提出了新的要求,如等离子平板显示器件（Plasma Display Panels,PDPs）已成为高清晰度大屏幕显示的佼佼者,具有易于实现大屏幕、厚度薄、重量轻、视角宽、图像质量高和工作在全数字化模式等优点,是发达国家竞相发展的高新技术产业,其要求荧光粉在真空紫外激发下发光效率高、色纯度好、热稳定性强、荧光寿命适当,对荧光粉的粒度、颗粒形貌及分散性也有比传统荧光粉更高的要求。白光LED（Light Emitting Diode,简称LED）具有体积小、发热量低、无热辐射、耗电量少、寿命长、反应速度快、环保无污染等优点,因此被认为将成为在全球半导体和照明领域的第四代固态照明光源。目前实现白光LED的主流方法是利用发光LED和相关荧光粉组合产生白光,需要荧光粉能够被近紫外-可见光有效激发产生高效的可见光发射和优良的温度淬灭特性。铝酸盐基发光材料已得到了广泛应用,但大部分存在很多不足,特别是在新型照明、显示器件上。如目前性能最好的BaMgAl₁₀O₁₇:Eu²⁺（BAM）蓝粉的稳定性较差,而PDP优良候选绿粉BaAl₁₂O₁₉:Mn²⁺（BHA）的发光效率与余辉时间有待改进。针对PDP与LED等照明显示器件的发展需要,本论文实现了通过Si-N键取代来优化铝酸盐荧光粉的光学性能和稳定性能。选取了两种典型的铝酸盐荧光粉BAM蓝粉和BHA绿粉,对Si-N掺杂前后的性质展开了一系列的分析,进一步深入分析其合成工艺、材料的晶体结构、光学性能、稳定性以及机理的优化,希望在研究其光学性能的基础上,以推动它在PDP与LED等新型照明、显示器件上的应用。本文第一章主要介绍了照明发展的历史,并简短介绍了相关文献,如固体发光材料、稀土离子光学特性、白光LED和PDP的原理和应用,并对常用荧光粉,特别是铝酸盐荧光粉的晶体结构、光学特性、优缺点等进行了介绍,最后提出了本论文的主要思路。第二章为实验部分。介绍起始原料、合成设备、合成工艺流程、性能表征方法等。第三章中通过高温固相反应合成Eu²⁺掺杂的BaMgAl₁₀O₁₇蓝粉（BAM）,并研究其光学性能和稳定性能,结果表明:在紫外-可见光谱中,BAM的激发主要来源于Eu²⁺离子中4f-5d的电子跃迁,波段位于220-450nm;在真空紫外光谱中,BAM的激发主要来源于基质晶格的吸收,有两个主要吸收波段,分别对应于晶体结构中的尖晶石层和镜面层,然后发生能量从基质晶格向Eu²⁺离子的转移。两种激发下的发射光谱范围都为400nm⁶00nm,发射峰值约为450nm,对应于激发态的5d能级向4f能级的电子跃迁。第四章探讨了首先通过一般的高温固相反应实现了Si-N在BAM荧光粉中的少量掺杂,少量的掺杂不影响晶体结构,只是小幅降低了晶胞参数;Si-N掺杂后,不管是真空紫外激发,还是紫外-可见激发,BAM的激发-发射峰形基本没有变化,除了峰位发生少量红移;最有意义的一点是,少量掺杂后,不管是原位荧光粉,还是高温热处理后的发光强度都得到了大幅度的提高。利用XANES图谱等发现,原位性能的提高是由于Si-N掺杂降低了发光离子周围的缺陷密度,而热处理后稳定性能的提高则是因为Si-N掺杂稳定了Eu²⁺离子。同时,我们发现,利用一般的高温固相反应所能实现的Si-N掺杂量很小,如果用分子式BaMgAl_10-xSi_xO_17-xN_x:Eu²⁺表示,获得最佳光学性能和稳定性能时的x=0.03,认为是由于热力学和动力学的影响,取代可能只是在表面发生,因而引入了高能球磨工艺,希望借助于高能球磨工艺实现较大量的Si-N键掺杂。通过对起始粉料进行高能球磨,实现了起始粉末的均匀非晶化,达到了原子级别的混合,从而将最佳光学性能和稳定性能时的x=0.25,说明高能球磨可以有效地提高固熔度,所得荧光粉具有更好的长期稳定性。最后,通过理论计算,发现Mg更容易取代尖晶石层中四面体位置的Al,而且分布在不同的尖晶石层中,而Si趋向于掺在导电层旁边的四面体位置,而N则趋向于掺在与Si相连的尖晶石层边缘的位置。同时发现,在最稳定取代情况下,金属离子和N之间的配位距离下降,说明取代的N和金属离子间的键能增加,可以有效抑制金属离子在镜面层中的移动,进而解释了少量的掺杂可以有效地稳定低价的Eu²⁺离子。第五章中通过高温固相反应合成BaAl₁₂O₁₉:Mn²⁺。研究紫外-可见光谱发现,样品的发射主峰位于517nm,归属Mn²⁺的⁴T₁→⁶A₁跃迁发射;而Mn²⁺的激发光谱则由多个谱峰组成,其峰值各为505nm,453nm,427nm,386nm,361nm,和280 nm,分别归属于⁶A₁→⁴T₁ （⁴G）,⁶A₁→⁴T₂ （⁴G）,⁶A₁→⁴E, ⁴A₁（⁴G）,⁶A₁→⁴T₂ （4D）,⁶A₁→⁴E（4D）和⁶A₁→⁴A₂（4F）的跃迁吸收。BHA中Mn²⁺的发光与Mn²⁺所处晶体场有关:当其处于八面体场中时发红光,处于四面体场中时发绿光。Mn²⁺在此只发绿光,由此可以推测Mn²⁺处于四面体场中。在真空紫外波段,BaAl₁₂O₁₉晶格可以有效地吸收能量,并转移给Mn²⁺,发射出明亮的绿光。第六章与第四章一样,分别通过高能球磨和固相反应法制备得到BaAl12-xSixO19-xNx:Mn²⁺荧光材料,高能球磨也可以有效地增加Si-N的取代浓度。利用光谱研究了基质中Mn²⁺的发光特性以及Si-N取代Al-O掺杂对其发光特性的影响。BaAl12-xSixO19-xNx:Mn²⁺样品的发射光谱为宽谱,最强发射峰位于517nm,归属Mn²⁺离子的⁴T₁→⁶A₁跃迁发射。而Mn²⁺的激发光谱则由多个谱峰组成,其中两个强峰峰值为453nm和427nm的可见光区,归属于Mn²⁺的⁶A₁→⁴T₂ （⁴G）和⁶A₁→⁴E, ⁴A₁（⁴G）的电子跃迁。Si-N掺杂后的发光强度明显高于未掺杂的BHA,并引起发射波长的红移。在荧光粉BaAl_12-xSi_xO_19-xN_x: Mn²⁺中,Mn²⁺都占据四配位的Al3+格位,在BaAl_12-xSi_xO_19-xN_x:Mn²⁺中配体N3-的电负性为3.04小于Mn²⁺在BHA中配体O2-的电负性3.44。根据电子云扩散效应, Mn²⁺在BaAl_12-xSi_xO_19-xN_x:Mn²⁺中的共价性大于BHA中的共价性,且晶体场能量强于BHA,故掺杂Si-N后BHA的发光性能得到了有效的提高。第七章通过对全文进行总结,对利用Si-N取代铝酸盐荧光粉中的部分Al-O来优化铝酸盐荧光粉的前景进行了展望。更多还原

【Abstract】 With the appearance of novel kinds of displays and lighting devices, such as plasma display panel （PDP）, light emitting diodes （LED）, field emission display （FED）, inorganic solid-state fluorescent materials are still very promising and therefore in the focus of current research activities. The phosphors should meet the requirement of the different devices. For example, thanks to its many advantages, including large screen, high definition, light weight and thin wall, plasma display panels （PDPs） are promising for large screen size displays. The phosphors for PDPs should have good color purity, high luminescent efficiency under vacuum ultraviolet （VUV） excitation, moderate decay time and high thermal stability. They still have high requirement on the particle size, size distribution and particle morphology. White light-emitting diodes （pc-WLEDs） are emerging as an indispensable solid-state light source for the forth generation lighting industry and display systems due to their unique properties including small volume, low heat radiation, energy savings, long persistence, short response time and environment-friendliness. The white light is often produced by the combination of phosphors and light emitting diodes. The phosphors should be efficiently excitated by near ultraviolet or blue lights and have high thermal quenching temperature.Aluminate-based phosphors have been widely used, but most of them could not be directly used in the new lighting and display devices. For example, the most widely used blue BaMgAl10O17:Eu²⁺（BAM） phosphors suffer from bad stability under thermal treatment or vacuum ultraviolet excitation. The PDP green phosphor candidate BaAl₁₀O₁₇:Mn²⁺（BHA） phosphors have low luminous efficiency and long decay time. To meet the requirements of PDPs and LEDs, we tried to optimize aluminate phosphors by substituting Si-N bonds for some Al-O bonds in aluminate phosphors. Systematical research has been done on the synthesis methods, crystal structure, photoluminescence properties, stabilities and optimization mechanisms of the aluminate phosphors before and after Si-N doping. After in-depth study on their luminescent properties, the aluminate phosphors are expected to find wide applications in novel lighting and display devices including PDP and LED.Chapter 1 starts with a brief description of the lighting history, followed by some related topics, such as solid state luminescent material, the optical properties of rare earth ions, the pricinples, the applications of white light LEDs and PDPs and some conventional phosphors. Then we especially reviewed the crystal structure, photoluminescence, advantages and disadvantages of aluminate phosphors. Finally, the main ideas of this doctoral dissertation were proposed. Chapter 2 is the experimental procedure, including the starting materials, synthesis equipments, the process synthesis, characterization methods, et al.In chapter 3, the Eu²⁺ doped BaMgAl10O17 （BAM） blue phosphors were prepared by high temperature solid state reaction method. The stability and optical properties of the obtained phosphors were studied. The results are shown as following: In the UV-visible spectrum, the excitation bands between 220 nm and 450 nm are orginted from the 4f-5d electronic transition of Eu²⁺ ions. In the vacuum ultraviolet spectrum, the energy was adsorbed by the BAM crystal lattice and transformed to Eu²⁺ ions, two excitation bands could be observed, which corresponding to the spinel crystal structure layers and mirror layers. The emission spectrum under either UV-visible or VUV lights consists of a broad emission band ranging from 400 nm to 600 nm with maximum at about 450 nm, which is characteristic of the 4f⁶5d¹→4f⁷ transition of Eu²⁺.In chapter 4, first of all, a small amount of Si-N has been introduced into the the BAM crystal lattice through high temperature solid state reaction. A small amount of doping did not affect the crystal structure, only slightly reduced cell parameters. Excitation-emission bands of BAM phosphors did not change after the incorporation of Si-N bonds, except a small redshift of emission bands under the excitation of either VUV excitation or UV-visible excitation. It should be emphasized that Si-N incorporated BAM （SiN-BAM） phosphors have significantly increased photoluminescence intensities compared with that of pure BAM phosphors before and after heat treatment in air at 600oC. According the XANES spectra et al, the improvements were due to the lower defect density for as-received SiN-BAM phosphors and due to the stability of Eu²⁺ ions for thermal treated SiN-BAM phosphors. However, we found that the Si-N concentration was very small by the high temperature solid state reaction. If the formula of SiN-BAM is BaMgAl_10-xSi_xO_17-xN_x:Eu²⁺, then the optimized photoluminescence properties and thermal stability were achieved when x equaled to 0.03. This suggests that the substitution occurs only in the surface of the BAM phosphors due to the thermodynamic and kinetic effects, so we tried high-energy ball milling to achieve high Si-N incorporation. Mechanical milling mostly transformed the starting powder mixture into an amorphous phase and homogeneity of elements at atomic level was achieved in amorphous phase. Thus, the optimized photoluminescence properties and thermal stability with a better long-term stability were achieved when x equaled to 0.25, Finally, a theoretical calculation has been done to search the preferential site for Si-N doping and Mg²⁺ ions. Mg²⁺ ions prefer to occupy the tetrahedral Al position of the spinel layer, and locate in different spinel layer of one cell. Si tends to occupy the tetrahedral Al position and link to the O in the conductive layer, N tends to link to the Si and lie at the edge of the spinel layer. The coordination distance between the metal ions and N in the most stable SiN-BAM crystal decreased, indicating that the N could effectively inhibit the movement of metallic ions in the mirror layer. This could explain that why the Eu²⁺ ions were stabilized with the small amount of Si-N incorporation.In chapter 5, the BaAl₁₀O₁₇:Mn²⁺ green phosphors were prepared by a high temperature solid state reaction method. Under UV-Visible excitation, each excitation spectrum consists of several narrow bands ranged from 270 to 515 nm. These bands are due to the spin-forbidden transitions in the 3d5 electron configuration of the Mn²⁺ ions. According to the Orgel diagram for divalent manganese, these bands peaking at about 505, 453, 427, 386, 361, and 280 nm are attributed to the transitions of ⁶A₁→⁴T₁ （⁴G）, ⁶A₁→⁴T₂ （⁴G）, ⁶A₁→⁴E, ⁴A₁（⁴G）, ⁶A₁→⁴T₂ （⁴D）, ⁶A₁→⁴E（⁴D）, and ⁶A₁→⁴A₂（⁴F）, respectively. Each emission spectrum consists of a broad green emission band ranging from 480 nm to 620 nm with maximum at about 515⁵18 nm, which is characteristic of the transition from the lowest excited state to the ground state of the Mn²⁺ ions, i.e., the ⁴T₁（⁴G）→⁶A₁（⁶S） transition. The emission of Mn²⁺ ions is related to the coordinating environment of Mn²⁺ ions. They show green emission in tetrahedral sites, but red emission in octahedral sites, incating Mn²⁺ in BHA locate in tetrahedral sites. Under VUV excitation, BaAl₁₀O₁₇ crystal lattice could efficiently adsorb energy and transfer to to Mn²⁺, and emit a bright green light.In Chapter 6, Si-N doped BHA （SiN-BHA） was obtained by high energy ball milling and solid state reaction, and the concentration of Si-N substitution could effectively increase by high-energy ball milling. The luminescence properties of Mn²⁺ were studied in terms of the Si-N incorporation. The emission spectra are dominated by a green emission band at about 517 nm, which is assigned to the transition from the lowest excited state to the ground state （⁴T₁（⁴G）→⁶A₁（⁶S）） of the Mn²⁺ ions. Each excitation spectrum consists of several narrow bands in the UV and visible regions, the two strong peaks of 453 and 427nm were attributed to the electronic transition from the ground state to the excited state （ ⁶A₁→⁴T₂ （⁴G）和⁶A₁→⁴E, ⁴A₁（⁴G） ） of the Mn²⁺ ions. The emission intensity of SiN-BHA phosphor is higher than that of the BHA phosphor and the emission wavelength had a little red shift. Mn²⁺ in SiN-BHA is tetrahedrally coordinated with mixed O^2- and N^3- ions. Because nitrogen has a lower electronegativity （χ（N）≈3.04） than oxygen （χ（O）≈3.44）, according to the electron diffusion effect, the covalence of Mn²⁺ in BaAl_12-xSi_xO_19-xN_x:Mn²⁺ was greater than that in BHA, and the crystal field energy was stronger than BHA, so the luminous performance of Si-N doped BHA was effectively improved.In chapter 7, a short conclusion has been made.更多还原