Development of Silicone Inorganic Oxide Encapsulating Materials for Light Emitting Diodes (LEDs) Applications

Autor: I-Ann Lei, 雷以安
Rok vydání: 2014
Druh dokumentu: 學位論文 ; thesis
Popis: 102
In our research, development of encapsulating material of light emitting diodes (LEDs) is the mainly purpose. In the first part (Chapter 2), optical hybrid materials with high refractive index were synthesis by in-situ production of titanium dioxide (TiO2) directly in a commercial-grade silicone resin via a sol-gel reaction. The optical transparency of the prepared TiO2/silicone hybrid film was investigated by UV-visible spectroscopy. These hybrid films with various TiO2 contents exhibited different refractive indices; the refractive index could reach 1.66 for the hybrid with 30 wt% of the TiO2. In addition, refractive index, thermal stability of the cured hybrid materials was also investigated. In the second part (Chapter 3), novel ZrO2/silicone hybrid materials (ZrO2/AB) useful for the encapsulation of light-emitting diodes (LEDs) are synthesized by an in situ sol-gel reaction of zirconium propoxide directly in a commercial-grade silicone resin by an in situ sol-gel reaction. By the chelation of the acetic acid, the ZrO2/AB hybrids exhibit high transparency owing to the well-dispersed ZrO2 particles in the silicone material, and their refractive index value also increased with increasing weight percentage of the ZrO2 in the hybrid. These high-refractive-index ZrO2/AB hybrids were then used as encapsulating materials to improve the luminous flux of the LEDs. From the results of the luminous flux measurement, the LED encapsulated with the pure silicone material has luminous flux of 3.97 lm. After encapsulated with the ZrO2/AB hybrid, the luminous flux of the LED was enhanced to a value of 4.35, which revealing that the increase in the refractive index of the encapsulating material by the incorporation of the ZrO2 could effectively improved the luminous flux of the LED, and these novel ZrO2/AB hybrids could also be considered as a suitable candidate as the encapsulating material for the LED. In the third part (Chapter 4), ZrO2 particles are synthesized directly in a commercial-grade silicone resin (AB) with the addition of a vinyl monomer (glycidyl methacrylate, GMA) by an in situ sol-gel reaction to obtain the silicone hybrid material (ZrO2/ABG). In addition to use the acetic acid as chelating agent, the addition of the GMA is able to retard the gelation rate of the metal alkoxide compound as well as the growing rate of ZrO2 during the sol-gel reaction, and also enhance the interfacial strength of the inorganic fillers with the silicone matrix by reacting with the silicone resin through a hydrosilation reaction via its vinyl group. The ZrO2/ABG hybrids thus exhibit excellent transparency and high refractive index. These ZrO2/ABG hybrids were then used as encapsulating materials to help the LEDs reach a higher luminous flux. Furthermore, according to the optical theory and the structure of the high-power LEDs, a simple simulation model was developed to estimate the luminous flux of the LEDs encapsulated with the ZrO2/ABG hybrids and the influence of the refractive index of the passivation layer on the luminous flux of the LEDs. Finally, with the help of this simulation model, an optimum combination of the encapsulating material and the passivation layer with appropriate refractive index values was obtained for achieving the highest luminous flux of LED. In the fourth part (Chapter 5), the purpose is to improve thermal mechanical property of the encapsulating materials in a very large temperature difference condition., thus decreasing the influence of the encapsulation on the reliability performance of the LED. The PBA(polybutylacrylate) oliogomer was firstly synthesized by a telomerization using 2-mercaptoethanol as a chain transfer agent. By the absorption to the inorganic particles and the carbonyl groups, the ZrO2 particles were produced on the oligomer chains of the PBA via an in situ sol-gel reaction to obtain the ZrO2-PBA composite particles, and subsequently mixed with a commercial-grade silicone resin to obtain the ZrO2-PBA/silicone hybrid materials (ZrO2-PBA/AB). The well-dispersed ZrO2-PBA domains lead to a high transparency and high refractive index of the ZrO2-PBA/AB hybrids, resulting in a higher luminous flux than the pristine silicone material. In addition to discuss the transmittance, refractive index, thermal resistance, and the water uptake of the ZrO2-PBA/AB hybrids, thermal stress evaluation of the LEDs encapsulated with the ZrO2-PBA/AB hybrids was also carried out in a thermal shock experiment with a temperature change from -35 °C to 125 °C within 15 mins. The results show that these ZrO2-PBA/AB hybrids have a lower thermal stress and exhibit a better mechnical resistance against the thermal shock, and the reliability performance of the LEDs are also greatly improved as encapsulated with the ZrO2-PBA/AB hybrids.
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