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We have improved charge character on the surface of phosphor particles by dispersed sub micro miter size sulfonate polystryrene beads and polyelectrolyte dispersant. The surface of TAG (Terbium Aluminum Garnet) phosphor was analyzed with TOF-SIMS (Time Of Flight-Secondary Ion Mass Spectrometer). Many hydrocarbon molecules were existed on the TAG phosphor. We could exchange the hydrocarbon into polyelectrolyte and sulfonated polystyrene beads. Characterization of the chemical bonging of polystyrene beads adhered on the surface of the TAG phosphor was archieved with x-ray photoemission spectroscopy (XPS) and FT-Raman. We could measure light efficiency of the white LED with integrating sphere spectrophotometer. Adhering sub micro miter size sulfonated polystyrene beads on the surface of TAG phosphor has enhanced extraction efficiency of light from phosphor. The sulfonated ligand and reduced difference of refractive index between phosphor and encapsulant material are responsible for the enhancement of extraction efficiency light from phosphor. Additional increase of light extraction has been observed when the phosphor particles were coated only on and near the LED chip. Surface modified phosphor particle and phosphor layer have improved LED light efficiency about ten percents.

The light extraction efficiency of side-view light-emitting diodes (LEDs) with a textured encapsulant top surface is analyzed theoretically and experimentally. A prism-type textured surface is proposed in order to increase the extraction efficiency, which is calculated by ray-tracing simulations. According to the simulation results, extraction efficiency can be enhanced by up to 35% compared with that of conventional LEDs. By using an imprinting technique to texture the encapsulant top surface, a prism-structure array has been fabricated. The experimental enhancement of light extraction efficiency is 14% for blue LEDs and 10% for white LEDs.

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