Sol–gel derived titania hybrid thin films with high refractive index

Incorporation of metal alkoxides into polymers through sol–gel process is of significant interest for tuning the refractive index of optical materials. In this paper, the organic–inorganic hybrid material with high refractive index (RI) and transparency was studied. Tetrabutoxytitanate (TBOT) and alkoxysilanes including diphenyldimethoxysilane (DPS) and γ-glycidoxypropyl trimethoxysilane (GPTS) were employed as sources of the titania sol and the silica sol, respectively. Two series of titania-based inorganic–organic hybrid materials with and without acetylacetone (AcAc) were prepared using the sol–gel method. Subsequently, crack-free films were fabricated by spin coating. The hybrid films with different Ti content were characterized by various techniques including IR, UV–vis, TG/DSC, SEM and auto-laser ellipsometer. The results indicated that the hybrid films displayed homogeneous morphology and titania was crosslinked with alkoxysilanes. Films without AcAc showed higher optical transparency in the visible region than those containing AcAc. The RI of films without AcAc increased from 1.54 to 1.64 at 633 nm with Ti molar fraction varying from 10 to 70%. Whereas, in the films with AcAc, the refractive indices were higher and unorderly. The study has demonstrated great potential to obtain titania hybrid films with high RI and transparency.