| 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+... |
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