| Summary: | 碩士 === 國立成功大學 === 電機工程學系碩博士班 === 98 === The object of this study is to synthesize phosphate oxide based phosphors. Our experiment is mainly seperated to two parts. First is to develop a suitable phosphor powder which can apply to UV light-emitting diodes(UV-LED). We successfully composed Ca9Y1-xTbx(PO4)7 (x=0.005~0.5) and Ca9Y1-xEux(PO4)7 (x=0.03~1) which can be excited by UV wavelength. We use Ca9Y(PO4)7 as the host material, rare earth elements like Tb3+ and Eu3+ as the luminescence center. We adjusted various different concentrations of Eu3+ and Tb3+ ions to investigate its luminescence mechanism and concentration quenching effect.
The experiments show that the color of emitting light is located at the range of blue-green to green in Ca9Y1-xTbx(PO4)7 (x=0.005~0.5) phosphor under UV light (370 nm) excitation, which has green emission at 544 nm. The maximum integral emission intensity is obtained at 20 mol% (x＝0.2) Tb3+, its C.I.E coordinate is (0.256,0.559), and the highest external quantum efficiency QE up to 16.8%. The color of emitting light is located at the range of orange-red to red in Ca9Y1-xEux(PO4)7 (x=0.03~1) phosphor under 395 nm excitation, which has red light emission at 613 nm. The maximum integral emission intensity is obtained at 100 mol% (x＝1) Eu3+, its C.I.E coordinate is (0.635,0.335), and the highest external quantum efficiency QE up to 40.8%. We also investigated the thermal stability, and we found that no matter Ca9Y1-xTbx(PO4)7 or Ca9Y1-xEux(PO4)7, both of which have better thermal stability than commercial phosphors. Finally, we blended these two different phosphors in weight percent to obtain a near- white light, its C.I.E coordinate is (0.322,0.333).
In the second part, in order to enhance the photoelectric conversion efficiency of solar cell, we look forward to using fluorescent materials to help transform the infrared light to visible light. Hence, we have chosen YPO4, Ca3(PO4)2, LaPO4 as the host materials codoped with Tm3+ and Yb3+ ions, and investigated the up-conversion effect of phosphate based phosphors under 980 nm laser excitation. We found that blue emission(1G4→3H6) and red emission(1G4→3F4) conclude two mechanism：one is sequential mechanism, the other is cooperative mechanism. The near infrared(NIR) emission(3H4→3H6) also concluded two mechanism：one is sequential mechanism, the other is cross relaxation effect between Tm3+ ions.
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