The Preparation, Luminescence Properties Of Eu³⁺-Doped Red-Phosphors Applied In Warm W-LED

Rare earth ions(RE) activated inorganic materials have been widely investigated due to their suitable spectroscopic characteristics to design luminescent or display materials. The key properties for LED using as phosphors are as followings: First, it should have large band gap and high absorption in VUV-UV region ultra-viola light(350-410 nm) or blue light(450-470 nm). Second, it should have high emission efficiency. Last but not least, the phosphor should have moderate phonon energy, as well as high physical and chemical stability. In this work, high temperature solid state method and Sol-gel method were used to prepare series of Eu3+-doped red phosphors. The structure was investigated by powder X-ray diffraction(XRD) measurement. The red emission intensities of presently studies compositions were investigated and compared with that of the commercial red-emitting Y2O2S:Eu3+. The photoluminescence QEs and decay curves were measured; The luminescence lifetime measurements were performed as a function of temperature. This is helpful for further investigation about the luminous properties of rare-earth(RE) doped various kinds of matrix.In chapter 3, a novel red-emitting nano-phosphor of Eu3+-doped Gd6 Mo O12 was successfully synthesized by the sol-gel method. The crystalline phase was confirmed by Xray powder diffraction analysis(XRD). The morphology of the nano-phosphor was analyzed by scanning electron microscopy(SEM), indicating a good crystallization with particles smaller than 500 nm. The luminescence properties such as photo-luminescence spectra and decay curves were investigated. The phosphors can be efficiently excited by near-ultraviolet(near-UV) light and exhibit a bright red luminescence around 613 nm ascribed to the forced electric dipole transition 5D0â†'7F2 of Eu3+ ions. The thermal stabilities were investigated from the temperature dependent luminescence decay curves(lifetimes) and spectra intensities. The luminescence properties related with applications in white light-emitting diodes(W-LEDs) such as absolute luminescence quantum efficiency, excitation wavelength, and color coordinates were discussed. The Gd6 Mo O12:Eu3+ nano-phosphor is a promising red-emitting candidate for the fabrication of W-LEDs with near-UV chips.In chapter 4, a series of red-emitting phosphors of MR2(Mo O4)4:Eu3+(M= Ba, Sr, Ca; R= La3+, Gd3+, Y3+) were prepared by solid-state reaction. The photo-luminescence excitation and emission spectra were investigated. The phosphors can be efficiently excited by near UV light and exhibit a red luminescence corresponding to the electric dipole transition 5D0â†'7F2 at 615 nm. The optimum doping in MY2Eux(Mo O4)4(M = Ba, Sr, Ca) were investigated by the dependence of luminescence quantum efficiency(QE) on the Eu3+ concentrations. The luminescence thermal satiability was checked by measuring the temperature-dependent luminescence intensities in the temperature region of 10-450 K. The results indicate that the three phosphors of Ba YEu(Mo O4)4, Sr Y0.6Eu1.4(Mo O4)4 and Ca Eu2(Mo O4)4 are the best choice for white-LEDs to be used for lighting. This was evaluated in details by taking into account of the properties such as the excitation spectra, luminescence QEs, red color coordinates, luminescence quenching of Eu3+-doping concentrations and thermal stability.In chapter 5, Eu3+-doped pyrophosphate ceramic Sr Zn P2O7 was prepared by the solidstate reaction method. The ceramic was investigated by XRD, SEM, photo-luminescence excitation and emission spectra, and decay curves. The micro-structure was investigated by the luminescence probe of Eu3+ ion. There are two kinds of Eu3+ luminescence centers, which occupy both Sr2+ and Zn2+ sites. The energy transfer could only be detected from the Eu3+ ions doped on Zn2+-sites to those on Sr2+-sites. The possible defects and charge compensation mechanisms were discussed on the base of crystal structure and luminescence properties.The innovations of this paper are as follows: 1) The luminescence properties, applications, and micro-structures of Eu3+-doped phosphors were systematically studied. Through the comparison of luminescence properties with the commercial red phosphor, all results indicate that the as-prepared phosphors are candidates for photoluminescence material for the white LED. 2) Two kinds of completing method were put forward to further optimize the preparation process, which find a new thought for phosphors preparation.