Synthesis And Characterization Of Optical Functional Hybrid Films Based On Sol-Gel Method

Nanomaterials have been widely researched for their unique properties on optical, electronics, magnetic properties and so on due to the size confinement. For example, the nanoparticles with high refractive index were widely used in high refractive composite materials, fabrication of antireflection coatings and nonlinear optical materials; while highly photo fluorescence (PL) semiconductor nanocrystals have wide applications in the fields of optoelectronic conversion device, optical display, sensor as well as biological imaging. However, the stability of the nanomaterials is not good enough because of their high surface energy, and this will limit their real applications, so it is necessary to incorporate them into inert materials. The sol-gel derived hybrid films are the ideal materials for their high stability and the simply procession. In this thesis, we have fabricated high refractive index and photoluminescent nanohybrid films respectively through sol-gel process and nanocrystal incorporation.In chapter Two, titanium butoxide was used as raw material, and co-hydrolysised with silicane coupling agent to prepare hybrid films. The reason we choose titanium butoxide is because of the high refractive index of its condensed production after hydrolysis possess. However, generally, the hydrolysis speed of titanium butoxide is extremely fast, the chelate agents were used to control the hydrolysis speed in traditional method, but it is not suitable in our system because they will affect the properties of the hybrid films. So, stepwise hydrolysis was adopted, and the obtained films have good properties, such as high and continual adjustment of refractive index from 1.47 to 1.73, high surface hardness of 4-5H and smoothness, high transmittance in visible range above 90% as well as good thermal stability.In the above sol-gel process and under low cured temperature, the obtained TiO₂ is amorphous. As we know, the refractive index of titania with crystalloid structure is higher than the amorphous phase, so, in chapter Three, we synthesized TiO₂ nanocrystals firstly, and incorporated them into hydrolyzed silicane coupling agent sol-gel system to prepare a series of high refractive index hybrid films. AFM analysis indicated that the films possessed good surface smoothness, and phase image illuminated the nanocrystals were well dispersed in the hybrid films without phase separation; Uv-vis spectra proved the hybrid films had good transparency; TGA indicated the films had good thermal stability (the temperature was about 200℃when the loss weight was 5%); Although the refractive index was not ideal, it reach to 1.66 with 50% weight content of TiO₂.In chapter Four, (3-Glycidyloxypropyl) trimethoxysilane was used to modify the surface of ZnO and CdTe nanocrystals respectively, after surface modification, ZnO nanocrystals can be existed stably in solution at room temperature, and the size increase and photoluminescence change were well controlled; for CdTe, the nanocrystals prepared in aqueous solution could be dispersed in methanol solution after surface modification, these two nanocrystals were incorporated into sol-gel system with hydrolyzed (3-Glycidyloxypropyl) trimethoxysilane. The results indicated the two types of hybrid films well inherited the luminescence of the nanocrystals; TEM illuminated the nanocrystals were well dispersed in the hybrid films without aggregation; Uv-vis spectra indicated the hybrid films had good transparency, and AFM illuminated the high surface smoothness of hybrid films. These thin films have potential use in flat panel displays, light-emitting devices and so on.