ZnO quantum dots-filled encapsulant for LED packaging

Abstract

For current LED packaging technology, one of the major limitations is the low light extraction efficiency, due to the refractive index (RI) difference between LED chip and air. Moreover, the trapped light in LED may convert into heat and further lower the conversion efficiency and reduction in the LED reliability. Encapsulants such as epoxy and silicone are usually added to reduce the RI contrast and enlarge the light escape cone. But the RI of epoxy or silicone is usually limited to 1.45 to 1.55. High RI particles can be added to help increase the RI of encapsulant. The particle size should be controlled smaller than one tenth of the visible light wavelength (400–800nm), in order to reduce Rayleigh scattering and increase the transmittance of encapsulant effectively. In this study, we prepared zinc oxide (ZnO) quantum dots (QDs)/epoxy nanocomoposites as LED encapsulant. The dispersion of QDs was further improved through the addition of exfoliated α-zirconium phosphate (ZrP) nanoplatelets (NPs). As a result, the RI of nanocomposites increased from 1.50 to 1.52 at 589 nm wavelength with 8 wt% filler loading while maintaining high transmittance. The solvent effect on RI was also investigated.