Novel ZrO2/silicone hybrid materials useful for the encapsulation of light-emitting diodes (LEDs) are synthesized by in situ sol–gel reaction of zirconium propoxide directly in a commercial-grade silicone resin. The domain size of the produced ZrO2 particles in the hybrid materials is controlled to be smaller than 350 nm based on SEM pictures to have a high optical transparency greater than 95% at 400 nm. The refractive index of the hybrid material increases from 1.52 to 1.62 when its ZrO2 content is increased from 1 to 15 wt.%. In addition, these hybrid materials are stable enough to tolerate the treatment of soldering at 260 °C for 2 min. For the hybrid materials with the ZrO2 content up to 7 wt.%, their weight-loss values are less than 0.25%. Finally, these hybrid materials are applied to encapsulate LEDs and their luminous flux is measured. The results showed that all the hybrid materials have higher luminous flux than the pristine silicone material. The luminous flux increased to a plateau value of 4.35 lm as the ZrO2 content in the hybrid material was increased to 3.0 wt.%. For all the hybrid materials studied here, the ZrO2/AB3 hybrid is considered to be the most suitable candidate as the encapsulating material for the LED used in this study.
Materials Chemistry and Physics 144 (1–2), p.41-48