| White Light Emitting Diodes (W-LED), due to the advantages of solidification, compact size, low heat, low power consumption, long lifespan, fast response and environmental, are widely applied in the areas of common lighting, backlighting and so on. At present, the commercialized W-LEDs are mainly assembled by a blue chip and yellow phosphor materia as Ce:YAG. The white light are generated from the mixture of blue light emitted by blue chip and the yellow light emitted by the yellow phosphor excited by blue light. Commercialized phosphor has been thought to be a great success; however, the phosphor of white LED still has many shortages, such as low efficiency, poor uniformity, large light decline, short lifespan and poor physical and chemical characteristics, which have negative effect on the performance of the W-LED.Therefore, this thesis puts forward the viewpoint that Ce:YAG single crystal fluorescent material with high quality produced by the czochralski method can make up the shortcomings of commercial phosphor powder; and that the optical performance of the single crystal white LED can be improved by doping rare earth ion like Gd, Pr, Sm, and Eu to increase the composition of red light in emitting light.X ray diffraction technology, absorption and fluorescence spectra analysis, light electric performance test are adopted to analyze the optical properties of Ce.YAG crystal(φ40×120mm) with high quality and Ce:YAG crystals (φ28×80mm) with doped Pr, Sm, Eu and Gd which are produced by the czochralski method. The research results are as follows:The absorption spectrum analysis shows that the5kinds of crystals——Ce: YAG, Gd, Ce:YAG, Pr, Ce:YAG, Sm, Ce:YAG, Eu, Ce:YAG have strong absorption at460nm, and match the GaN blue chips with a luminescence center of460nm. The fluorescence spectrum analysis shows that these five kinds of crystal plates can be excited by the460nm blue light; and the reasons that lead to fluorescence emission are also analyzed. The doping of Gd3+ion can convert its luminescence to red shift, thus increasing the red components of emitted light.The doped wafers in Pr3+and Sm3+can not only produce red light emission by transferring energy to Pr3+or Sm3+ion through Sm3+ion, they also improve the luminous efficiency by means of increasing Ce3+s absorption of blue light, for Pr3+and Sm3+have sensitizing effect to Ce3+s glow.The doping of Ce3+ion does not produce red light emission, on the contrary, it generates quenching effect on the luminescence of Ce3+ion, which greatly reduces the luminous efficiency, but improves the color rendering index.We have tested the light-color-electricity performance of the white light LED which consist of five crystal samples. Studied the influence of the chip thickness and operating current magnitude to the illumination of the white light LED. The result showed that all of these five kinds of white light LED can produce the white light. The more thick the crystal plate is, the lower the colored index of LED is. While the magnitude of operating current has less influence on the colored index of white light LED. |
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