【作者】 陆青山；

【导师】 李建功；

【作者基本信息】 兰州大学 ， 材料物理与化学， 2010， 博士

【摘要】 介孔氧化硅具有独特的结构,比如有序的孔道、均一的孔径分布、大的比表面积和非晶态的无机骨架。这些特性可以使它作为功能性客体材料如金属、氧化物和有机基团的主体材料,利用孔道空间限域效应,起到控制这些客体材料的尺寸大小,达到客体材料的分散。在过去的十年时间,基于介孔氧化硅的功能性杂化材料被广泛研究。这种杂化材料的制备是基于将介孔材料作为硬模板在其孔道内引入前驱物的思想,使客体材料在介孔材料孔道中限域生长,所以前驱物溶液的浸渍过程是至关重要的步骤。此外,当客体材料颗粒尺寸降到纳米尺度,尤其是性能受量子尺寸效应影响明显的半导体材料在光电方面具有优异的性能。因此,开发一种简单、有效的组装法将半导体材料组装到介孔材料孔道中,实现其不同于块体材料的性能,是非常有理论和现实意义的。另外,硅酸盐材料具有高的热稳定性和化学稳定性、高的发光效率以及可见光范围的光学透明性,是理想的稀土离子和过渡族金属离子发光中心的基质材料。传统高温固相法是制备硅酸盐发光材料的主要方法,但这种方法存在一些缺点：比如高的反应温度容易使颗粒结块,形成大颗粒,后续的研磨过程会引入一些缺陷,使发光性能降低。介孔材料具有高的孔隙率和大的比表面积,这将增加氧化硅的吉布斯自由能以及与反应物之间的接触面积。因此,可以把介孔氧化硅作为反应物来合成新材料。将不同的氧化物组装到介孔氧化硅孔道内,原则上可以通过煅烧得到相应的硅酸盐材料。到目前,利用介孔氧化硅作为反应物来制备硅酸盐材料,进而作为稀土离子或过渡族金属离子的基质材料的研究报道很少。此外,Eu3+的发光特性对所处格点的对称性非常敏感,介孔氧化硅材料具有不同于溶胶凝胶氧化硅的独特结构,可以将介孔氧化硅作为Eu3+的基质材料。本工作中,我们利用介孔氧化硅的孔道、孔壁和表面积等特性,制备出具有分立中心发光和复合中心发光的发光材料,并对其结构和发光特性进行了研究,具体的研究内容如下：利用两溶剂法在介孔材料SBA-15中组装ZnO团簇,得到ZnO/SBA-15纳米复合材料。ZnO含量高的ZnO/SBA-15纳米复合材料保持有序的二维六方介孔结构。ZnO以非晶态或团簇的形式稳定存在于SBA-15的孔道中。室温下的发射峰经高斯拟合成三个峰：位于367 nm的发射峰归属于ZnO的近带边发射,420 nm处的紫光发射是由局域在SBA-15和团簇ZnO界面耗尽层中的缺陷态与价带之间的辐射跃迁导致的,457 nm处的蓝光发射是ZnO中的氧空位或间隙锌引起的。由于受SBA-15孔道限域空间作用,ZnO表现出量子尺寸效应,禁带宽度变宽,近带边发射向短波长方向移动,发生了显著的蓝移。这对于开发短波长发光材料具有重要的意义。以萃取介孔材料SBA-15为硅源,在800℃下煅烧2 h得到锰掺杂硅酸锌(Zn2SiO4：Mn2+)发光材料,该煅烧温度明显低于传统固相反应的煅烧温度,同时也低于以退火SBA-15为硅源时的煅烧温度。这主要是由于萃取SBA-15具有丰富的孔道、大的比表面积、非晶态孔壁和内表面高密度的羟基,这些因素可增加氧化硅的吉布斯自由能,增大反应物之间的接触面积,提高反应动力学,进而降低反应温度。紫外光245 nm激发下,发光中心Mn2+直接被激发；在真空紫外147 nm激发下,激发能量被基质晶格吸收并通过交换作用传递到发光中心Mn2+,伴随着Mn2+从激发态跃迁到基态,产生527 nm的绿光发射。在245 nm激发下,发射强度最强的掺杂浓度为0.06即样品Zn1.94Mn0.06SiO4。在147 nm激发下,样品Zn1.94Mn0.06SiO4的衰减曲线呈双指数函数关系,经拟合得到的平均寿命为8.87ms,这一数值与报道的8-16 ms相一致。采用介孔氧化硅SBA-15模板路线,以SBA-15作为无机硅源,通过高温固相反应在1300℃下制备出铕掺杂的硅酸钇(Y2SiO5:Eu3+)发光材料。Y2SiO5:Eu3+结晶性好、颗粒致密、表面光滑、颗粒大小在微米尺度。发射光谱显示了Eu3+的特征发射,且Eu3+占据对称性低的格位。传统高温固相法制备稀土离子掺杂的硅酸钇发光材料,在加助溶剂情况下,煅烧温度需要1500℃。我们采用的制备方法煅烧温度有显著的下降。对比实验结果表明：介孔氧化硅SBA-15与氧化钇的反应速率高于球状氧化硅与氧化钇的反应速率(介孔氧化硅的颗粒尺寸大于球状氧化硅的颗粒尺寸)。反应温度的降低和反应速率的加快主要是归功于介孔材料SBA-15具有高的孔隙率、大的比表面积,这极大地提高了反应物之间的接触面积,缩短了扩散距离,加快了反应动力学,降低了反应温度。SBA-15在高温固相反应法制备硅酸盐材料显示了很大的优势,可用于制备其他硅酸盐材料。以三嵌段共聚物F127为结构导向剂,通过溶胶凝胶和蒸发诱导自组装技术,利用旋涂法在不同基底上制备出Eu3+掺杂立方介孔氧化硅薄膜材料。介孔薄膜的介观结构具有体心立方对称性,薄膜连续、光滑、没有微裂纹,厚度大约为205 nm。当Eu3+的掺杂量达到5.24%(Eu／Si),煅烧温度为600℃,薄膜仍然保持高度有序性。激发光谱显示出波长位于246 nm处的Eu3+-O2-电荷迁移带,说明掺杂在薄膜中的Eu3+与O2-形成键合。发射光谱中观察到Eu3+的两个特征发射峰,分别是非简并能级5D0到轨道-自旋耦合简并能级7FJ(J=1,2)的辐射跃迁。电偶极5D0-7F2的发射强度高于磁偶极5D0-7F1,表明Eu3+所占据的格点对称性低。掺杂浓度高于3.41%(Eu／Si),有浓度淬灭发生,这一浓度要高于Eu3+在非晶态氧化硅中的淬灭浓度1.2%。这可能是由于介孔薄膜具有非晶态骨架和高的比表面积,表面上大量的非成键O2-与Eu3+配位补偿电荷,降低了Eu3+形成团簇。更多还原

【Abstract】 Mesoporous silica exhibits novel structures such as ordered porous structure, uniform pore size distribution, large surface areas, thick and amorphous frameworks, which make them as excellent hosts for distribution of functional guest species like metals, oxides, and organic groups. Hybrid materials based on mesoporous silica with novel properties have been studied extensively during the last decade. The general route for preparing hybrid materials is to introduce precursors into the pores of mesoporous materials, and the guest species could grow in the pores. Therefore, a crucial step in the above process is the impregnation of the precursor. The semiconductors usually exhibit quantum size effects and show different electric and optical properties from bulk materials, when their particle size decreases to nanometer scale. Because of confined growth of nanostructures due to the volume space effect of pores, it is important to develop a simple and low cost novel strategy to incorporate semiconductors into mesoporous silica achieving novel properties.In addition, silicate is a well-known host material for rare earth or transition metal activators due to its high visible-light transparency, excellent luminescence efficiency, and chemical stability. Up to now, the traditional solid-state reaction process is mainly employed to produce the commercial silicate phosphors with high crystallinity and efficient luminescence. However, the traditional solid-state reaction method has drawbacks such as high reaction temperature, agglomerates, and long grinding. Because of nanoscale pores and large surface areas, mesoporous silica could be used as a reactant for preparing new materials. Various silicates should be obtained by calcination in principle, if different guest oxides are incorporated into the pores of mesoporous silica. Till now, no systematic works on the synthesis of silicate doped with rare earth or transition metal ions by mesoporous template route has been reported. In addition, in comparison to bulk sol-gel silica, ordered mesoporous silica provides unique structures; the luminescence of Eu3+ ions can be used to probe the chemical environment of the Eu3+ ions.In this work, the luminescence materials based on mesoporous silica were prepared, and their structures and photoluminescence properties were studied. The studies are as follows.The two-solvent method was employed to prepare ZnO clusters encapsulated in mesoporous silica SBA-15 (ZnO/SBA-15). The ZnO/SBA-15 nanocomposite has the ordered hexagonal mesostructure. ZnO clusters are distributed in the pores of SBA-15. The photoluminescence spectra show the emission band centered at about 370 nm which can be fitted by three emission Gaussian peaks:the UV emission band around 367 nm, the violet emission around 420 nm, and the blue emission around 457 nm. The UV emission is attributed to near band-edge emission of ZnO. The violet emission results from the oxygen vacancies on the ZnO-SiO2 interface traps. The blue emission is from the oxygen vacancies or interstitial zinc ions of ZnO. The UV emission shows a significant blue shift due to quantum size effect compared to the emission of the bulk counterpart reported. The ZnO clusters encapsulated in SBA-15 can be used as ultra-violet light-emitting material.Mn2+ions-doped Zn2SiO4 (Zn2SiO4:Mn2+) powders were prepared by solid-state reaction using extracted SBA-15 as silica source. The well crystalline willemite Zn2SiO4:Mn2+ can be obtained at 800℃which is much lower than the conventional solid state reaction temperature and lower than using the calcined SBA-15. The reason is that the extracted SBA-15 provides large surface area, high density silanol groups, and large pore size, which may increase the reaction interfaces, enhance the reaction kinetics, and decrease the reaction temperature. Ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectra reveal the host lattice absorption band around 162 nm and the charge transfer transition band around 245 nm. The Zn2SiO4:Mn2+ phosphor exhibits a strong green emission around 527 nm. The Zn2SiO4:Mn2+ phosphor with the Mn2+ doping concentration of 0.06, i. e., Zn1.94Mn0.06SiO4, shows the highest relative emission intensity. Upon 147 nm excitation, the luminescence decay time of the green emission of Zn1.94Mn0.06SiO4 around 527 nm is 8.87 ms, which is consistent with the value of 8-16 ms as reported. Eu3+ ions-doped Y2SiO5 (Y2SiO5:Eu3+) samples were prepared by solid-state reaction at a calcination temperature of 1300℃using SBA-15 as silica source without fluxes. The results show that the crystalline Y2SiO5:Eu3+ particles are dense, weak agglomeration, and have a morphology similar to SBA-15. The characteristic luminescence shows the Eu3+ locate at low symmetric sites. The reaction temperature is lower than that of 1500℃in conventional solid-state reaction with fluxes. Also, the reaction rate between Y2O3 and SBA-15 is faster than that between Y2O3 and SiO2 powder based on our comparison experiments (The particle size of the SiO2 powder is smaller than that of SBA-15). This is attributed to the high reactive activity of SBA-15 with porous structure and large surface areas, which can enhance the Gibbs free energy, increase the reaction interfaces, reduces the diffusion distance, and decrease the reaction temperature. This synthesis route may also be applied to prepare other silicate materials at relative low calcination temperature by solid-state reaction.Eu3+ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared using triblock copolymer as a structure-directing agent using sol-gel spin-coating and calcination processes. The mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu3+ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of 5D0-7F1 and 5D0-7F2 of Eu3+ ions located in low symmetry sites in mesoporous silica thin films. In our work, the fluorescence quenching concentration of 3.41%is higher than that of 1.2% in non-templated sol-gel silica. The mesoporous silica thin films provide enough non-network oxygen species to coordinate and charge compensate the Eu3+ ions, which may enhance the overall solubility and reduce the aggregation of Eu3+更多还原