| Since1990s, the first white LED was reported, which was made up with InGaN blue chip and YAG:Ce yellow phosphor powders. The principle of the white LED is as the following:InGaN chip emits blue light. YAG:Ce phosphor powders are excited by the blue light and then emit yellow light. The yellow light and the leftover blue light are mixed to form white light with quite good color rendering index and very high luminance. There are more advantages with this white light, such as only using one chip, simple circuit design, easy to control and low cost. Compared with the other lights, the white LED has other advantages of lower power consumption, lower voltage, better color, longer life, etc. Therefore, it becomes the most potential solid light source to replace the traditional incandescent lamps, fluorescent lights. With a vast market value and the praise of the community, preparing the high color rendering, high luminous efficiency of phosphor is particularly important. Because the YAG:Ce yellow phosphor is a key component for white light emitting diode, this phosphor attracts more and more attentions. However, due to commercial interests, the best recipe and sintering process are still confidential. Therefore, to investigate the best recipe and sintering process is imperative. As mentioned before, the white light is a mixture of the yellow light and blue light emitted from yellow phosphor YAG:Ce3+and GaN blue LED, respectively. However, due to the lack of red ingredients, its color temperature is high, the color rendering index is also very low. In order to obtain high-quality white LED, one of the most effective and feasible methods is:with violet or ultraviolet light as a light source, exciting three phosphors, red, green, blue. Using lens, the three beams of the color light are controllably mixed to get white light. Eu3+doped NaLa(WO4)2phosphors can be effectively excited by near ultraviolet region (380nm-410nm) light, and the energy absorbed can be smoothly passed from the NaLa(WO4)2matrix to the activated ions of Eu3+Eventually Eu3+doped NaLa(WO4)2phosphors emit red light. Based on the above analysis, we prepared the yellow phosphor YAG:Ce3+with a solid state reaction method and prepared NaLa(WO4)2:Eu3+phosphor with hydrothermal reaction method. Their phosphor luminescence properties were studied. In addition, in order to obtain yellow light emission, NaLa(WO4)2:Ce3+phosphor were also prepared and their structures, morphologies, and light emission properties were studied. The main research contents of this paper are summarized as follows:(1) A solid state reaction method was used to prepare a series of YAG:Ce3+phosphors with different Ce3+doped concentration under different sintering conditions in order to find a recipe formula and the best sintering process. The experimental results show that:when the excitation wavelength is460nm, the phosphors emit light with wavelength of540nm; The optimum doping of Ce3+concentration and sintering temperature were2%and1400℃, respectively. In addition, the emission wavelength shows a red-shift phenomenon by analyzing its spectrum, which favorably meets the need of modern solid-state lighting.(2) With a hydrothermal method, NaLa(WO4)2:Eu3+and NaLa(WO4)2:Ce3+phosphors were prepared. The former emit strong light with the wavelength locating around614nm when excited with a near violet source, and it is a the red phosphor. The latter only emit strong near red light at774nm when excited with a near violet source (wavelength=340nm). It is interesting and exceptional that such a big energy conversion span is realized in this system.. |
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