High refractive index and transparency nanocomposites as encapsulant for high brightness LED packaging

Improving the light extraction efficiency is one of the key technologies for high brightness LED packaging, and is of great importance for the semiconductor illumination industry. Due to the large refractive index (RI) difference between LED chip and outside medium, the light will be trapped in the LED, convert into heat, and further lower the conversion efficiency. Encapsulants such as epoxy and silicone are usually added to decrease the RI contrast and increase the angle of light escape cone. But the RI is usually limited to 1.45 to 1.55. Higher RI particles can be added to further increase the RI of LED encapsulant. The particle size should be controlled smaller than one tenth of the visible light wavelength, in order to reduce Rayleigh scattering. In this study, we prepared TiO₂ nanoparticles/silicone nanocomoposites as LED encapsulant. The dispersion of nanoprticles was further improved through silane treatment. As a result, the RI of nanocomposites increased from 1.54 to 1.62 at 589 nm wavelength with 5 wt% filler loading while maintaining high relative transmittance.