Zirconia/phenylsiloxane nano-composite for LED encapsulation with high and stable light extraction efficiency

Abstract

To obtain a rapid processible LED encapsulant that leads to high and stable light extraction efficiency (LEE), UV curable ZrO₂/phenyl-siloxane nano-composite (ZSC) double-layer encapsulants were prepared and optimized. The highly crystalline ZrO₂ nanoparticles with a diameter of ∼14 nm were synthesized through a modified hydrothermal method at mild conditions, and a UV curable methacryl-diphenyl-polysiloxane (MDPS) with a refractive index (RI) of 1.54 (at 633 nm) was synthesized from self-condensation of diphenylsilanediol and an end-capping reaction. High refractive indexes (RIs) from 1.54–1.61 have been obtained for ZSC composites by adding 0–20 wt% ZrO₂. Before and after sulfur vapor erosion, the double-layer encapsulated sample (M-10/M) showed 11.2% and 64.8% higher LEE respectively than that of Dow Corning OE-7662. Meanwhile, the variation of LED light color temperature (T_c) was less than 1%. The effect of the ZrO₂ nanoparticle content on LEE of double-layer and single-layer encapsulation were compared and discussed based on Fresnel loss and Rayleigh scattering theories. The double-layered UV curing processing took only 1/6 of the time needed for common thermal curing.