There are many ways to produce white light emitting diodes (WLEDs), such as applying yellow phosphors to a blue light-emitting diode chip, applying red and green phosphors to a blue light-emitting diode chip, mixing red, green, and blue light-emitting diode chips or applying blue, green, and red phosphors to a UV light-emitting diode.
Compared to a traditional incandescent light bulb, a white light-emitting diode has some advantages, e.g. long lifetime, low power consumption, small volume, fast response time and good shock-resistance, and thus light-emitting diodes are gradually replacing traditional lighting products. As a result, in the lighting market, auxiliary lighting, including flash lights, car interior lights, architectural decorative lighting products, is still the main market of white light-emitting diodes, while still white light-emitting diodes are expected to replace traditional lighting products in the future to become the mainstream of the global lighting market. However, current white light emitting diodes still need to overcome the problems such as heat dissipation, inadequate brightness and relatively high price.
In addition to package techniques, phosphor material is also an important factor affecting luminous efficiency of a light source. Thus, solid state lighting companies are devoted to modifying phosphor compositions to increase phosphor conversion efficiency. The color rendering index of the white light generated by a yellow phosphor excited by a traditional single blue chip is low and thus the color saturation of an object illuminated by such white light is poor, thereby lowering the commercial lighting market value. Recently, it is found that using a high efficient UV-light-emitting diode (UV-LED) as an excitation light source is another way of white light emitting diodes to become lighting devices. Because the UV-LED technique is gradually developed, the phosphor development for matching to the emission wavelength of UV-LEDs and thus manufacture white light emitting diodes with high efficiency and high brightness becomes important.
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