| Summary: | 博士 === 逢甲大學 === 電機與通訊工程博士學位學程 === 104 === White light-emitting diodes (LEDs) are an optimal candidate for generating white light source. Compared with traditional lighting sources, white-light LEDs offer the benefits of low energy consumption, are free of mercury pollution, and are small, lightweight, durable, and reliable. However, most products exist in blue light, UV leakage, and glare problems with commercial phosphor-based white-light LEDs. The long-time exposure to blue or UV light can damage the skin, eyes, and endocrine system of humans. Therefore, if LEDs are to be promoted as a next-generation light source, problems related to the safety of these devices must be solved. Accordingly, this thesis devotes to investigates of UV- and blue-light-inhibited white LEDs. Firstly, an RGB phosphor-converted white LEDs with a coating layer of photocatalyst is proposed. Using the absorption spectrum in the blue and UV regions of the bismuth oxide photocatalysts, the blue light and UV leakage problems of phosphor-converted white LEDs can be significantly reduced; meanwhile, the coating layer of photocatalyst can act as an air purifier and diffuser to reduce glare. In order to optimize the suppressed ratio of UV-light and increase the luminous efficiency, the improved design of an RGB-phosphor-converted white LED is proposed. In the design, the LED package is covered with a substrate that has an optical reflection coating on the underside and a bismuth oxide photocatalyst coating on the topside. The wavelengths below 400 nm are reflected back to re-excite the red-green-blue phosphors and consequently enhance luminous efficiency. The absorption spectrum of bismuth oxide photocatalysts is below 521 nm, and the leaked UV and blue light can be absorbed, thereby exciting electron-hole pairs and producing the photocatalytic effect. Thus, blue light and UV leakage can be suppressed appreciably and the luminous efficiency can be increased markedly. Finally, a packaged design of different viscid epoxy resin on RGB phosphor-converted white light-emitting diodes to improve the problem of phosphor precipitation is proposed. Because the more viscid epoxy resin has a uniform distribution of RGB phosphors in SMD-LED lead frame, which can be more efficiently excited by ultraviolet (UV) LED chip. Therefore, the uniform distributions of RGB phosphor with the higher viscid epoxy resin can provide uniformed light field and comfortable visual experience. Accordingly, the concepts of above packaged can be applied effectively to implement a health, safe and environment benign white LED light source.
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