High Refractive Index and Transparent Nanocomposites as Encapsulant for High Brightness LED Packaging

A high refractive index (RI) and transparent encapsulant material is in great demand for light emitting diode (LED) packaging to lower the RI contrasts between a LED chip and an encapsulant, and therefore improve the light extraction efficiency. In this paper, we prepared TiO₂/silicone nanocomposites and studied the effects of the crystalline phases of TiO₂, and the TiO₂ surface modifications on their optical properties. The rutile TiO₂ was found to be more effective to increase the RI of the nanocomposite than the anatase phase TiO₂. At a 5 wt.% loading of TiO₂, the RI was as high as 1.62 at the wavelength of 589 nm, which represents a significant improvement from 1.54 for silicone resin. In addition, surface modification was carried out using vinyl-terminated silane to improve the dispersion of nanoparticles in a silicone matrix, leading to a high relative transmittance of 84%. We also demonstrated that the optical property degradation of the nanocomposites in this paper was negligible after the accelerated reliability test.