Abnormally high optical transmittance of refractive-index modified ZnO / organic hybrid films

Hybrid films consisting of ZnO nanoparticles and organic matrices were fabricated at particle concentration levels of up to 60 wt%. The correlation between the refractive index and optical transmittance in the visible light region was investigated. The refractive index of the hybrid films was modified in a continuous manner in the range from 1.44 to 1.55. The refractive index increased linearly as a function of particle concentration. On the other hand, optical transmittance showed little change above the particle volume fraction of 0.08.

I. Introduction

Uniform dispersion of nanoparticles in organic materials enables modification of the overall refractive index of the nanocomposites in the range between the indices of nanoparticle and organic materials [1]. Such hybrid materials have been attracting much attention as novel refractive index engineering materials for a wide range of optical applications including planar-gradient index lenses, reflectors, optical-wave guides, optical adhesives, anti-reflection films, holographic information storage devices and optical coupling materials [2]. Of particular importance for those applications is high optical transmittance at the wavelength of interest [1]. However, there is a trade-off between high refractive indices and high transparency. A high particle loading level not only leads to a high refractive index of the hybrid films but also increases light-scattering intensity, leading to low transparency [3].