Synthesis And Photoluminescence Properties Of Phosphates And Pyrophosphates Doped With Rare Earth Ions For White LEDs

Due to the unique electronic shell structure of rare earth elements, the luminescent materials activated by rare earth ions usually have excellent optical properties. Moreover, the luminescent materials based on phosphates and pyrophosphates have good chemical stability and thermal stability. Therefore, the investigation on phosphates and pyrophosphates phosphors for LEDs has attracted more attention recently. In this thesis, I synthesized a series of phosphates and pyrophosphates phosphors and investigated their optical properties:1. Eu2+doped Ba1.6Cao.4P207phosphors were prepared by high temperature solid state reaction method. The photoluminescence (PL) properties and energy transfer of Ba1.6Ca0.4P207:Eu2+phosphors were investigated. The PL excitation and emission spectra reveal that the doped Eu2+ions occupy two different crystallographic sites. The concentration dependence of PL emission spectra indicates that energy transfer between two different Eu2+ions takes place. Decay kinetics of donor (Eu2+(1)) and acceptor (Eu2+(2)) ions luminescence have also been analyzed. The possible energy transfer mechanism and the temperature dependence of the Eu2+luminescence decay kinetics have also been investigated in detail.2. Eu2+and Mn2+doped phosphors in the novel system Ba1.6Ca0.4P207were synthesized through high temperature solid state reaction. The PL property of Eu2+Mn2+in Ba1.6Cao.4P207were reported and discussed. The emission spectrum of Ba1.6Ca0.4P2O7:0.04Eu2+consists of two distinct broad bands peaking at about400and470nm, and the excitation spectra exhibit broad band in the range of250to400nm. A broad yellow emission band is observed around565nm in Mn2+single doped sample, and the intensity can be enhanced by co-doping Eu2+ions. It also reveals that the energy transfer from Eu2+to Mn2+occurs in this host lattice.3. Ba1.6Cao.4P207:Ce3+, Tb3+phosphor was synthesized by the method of high temperature solid state reaction, the emission and excitation spectra and energy transfer of Ce3+and Tb3+in Ba1.6Cao.4P207were also investigated. Under excitation at280nm the emission spectrum of Bai.6Cao.4P207:Ce3+consists of a peak at370nm and a shoulder at the longer wavelength side. The emission spectra of Ba1.6Cao.4P207:Tb3+shows the well-known emission lines due to5D4-7FJ transitions of Tb3+. The green emissions of Tb3+ions are enhanced upon UV excitation through energy transfer from Ce3+to Tb3+ions. The efficiency of such an energy transfer is estimated based on spectroscopic data.4. Ba3P4O13:Eu2+phosphor was synthesized by the method of high temperature solid-state reaction. The doped Eu3+ions can almost be reduced to Eu2+ions in air atmosphere at high temperature. Besides, the kind of abnormal reduction can be explained by charge compensation mechanism. The fact of the doped Eu2+ions occupy two different Ba2+sites is confirm by PL emission spectrum and luminescence decay kinetics. The PL excitation spectrum shows a broad band which matches well with the emission of near UV chip. Ba3P4O13:Eu2+is a promising phosphor for near UV chip excited white LEDs.5. Eu2+doped Sr3P4O13phosphors were prepared by high temperature solid state reaction method, the emission and excitation spectra of Eu2+in Sr3P4O13were also investigated. Excited the phosphors by ultraviolet light with different wavelength, the position and appearance of the emission peak are almost the same. The emission spectrum situates at about408nm. The optimum concentration of Eu2+is x=0.08.6. Ca3Mg3(PO4)4:Eu2+phosphors were synthesized by the method of high temperature solid state reaction. The PL properties of Eu2+in Ca3Mg3(PO4)4were reported and discussed. It is concluded that the wavelength of the emission peak is450nm and the optimum concentration is x=0.08. The wide range of the excitation spectrum matches well with the emission of near UV chip. Therefore, Ca3Mg3(PO4)4:Eu2+phosphor is a promising blue phosphor for white LEDs.