Effect of Glass Refractive Index on Light Extraction Efficiency of Light‐Emitting Diodes

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Abstract
Light‐emitting‐diode ( LED ) encapsulants, such as epoxy and silicone resin, have a lower refractive index than YAG :Ce phosphor, and this is usually one of the major causes of LED inefficiency. To improve LED performance, a glass encapsulant is considered. In this study, the SiO 2 – B 2 O 3 – ZnO glass system containing La 2 O 3 and WO 3 was investigated as an encapsulant to minimize total internal reflection and to increase the light extraction efficiency of LED packages. The characterization of glass encapsulants was performed using a differential scanning calorimeter, a pycnometer, a prism coupler, X ‐ray photoelectron spectroscopy, and integrating spheres. The refractive index increased linearly with increasing molar volume of glass because La 2 O 3 and WO 3 act as modifiers in the glass, creating more nonbridging oxygen. The refractive index of glass increases with the content of La 2 O 3 and WO 3 , which is attributed to the increase in polarizability of oxide ions in the glass. When the refractive index between glass and phosphor matched, light extraction efficiency was maximized because total internal reflection decreased.
Funding Information
  • Technology Innovation Program (10044203)
  • Ministry of Trade, Industry & Energy

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