The Preparation And VUV Luminescence Research Of Rare Earth (Eu²⁺, Eu³⁺, Ce³⁺, Tb³⁺) Doped Orthophosphate

The rare earth (RE) doped orthophosphate material is an important kind of the luminescence materials. Eu2+, Eu3+, Ce3+ and Tb3+ are widely used in the luminescent materials as dopant. Due to the vacuum ultraviolet (VUV) luminescence properties and good stability of orthophosphate material, it obtains a lot of attention on the display and illumination field. Then, the research in VUV luminescent properties of RE doped phosphate is useful for finding suitable PDP phosphors.In this paper, rare earth ions Eu2+, Eu3+, Ce3+ and Tb3+ are selected as the dopant, and four orthophosphates: NaSrxBa1-x(PO4), SrZn2(PO4)2, NaCaPO4 and Na2CaMg(PO4)2 are selected as the host materials. These materials are prepared by high temperature solid-state reaction method or Sol-gel method. The structure and luminescence properties of the four orthophosphates are measured respectively; the mechanism of emission is discussed; the chrominance and decay of the emission under the excitation at VUV have been analyzed; and applications potential are discussed.In the third chapter, the preparation process of RE (Eu2+, Ce3+, Tb3+) doped NaSr0.55Ba0.45(PO4) is discoursed. Through the test of X-ray diffraction (XRD), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), the structure and feature of the phosphors are discussed. In the excitation spectra, the broad absorption peaks in the VUV region are due to the electron transition between the conduction band and the valence band of the host orthophosphate materials. The peaks in the UV region are due to the electron transitions among electron levels of RE ions: absorption peaks of Eu2+ are from the 4f7→4f65d transitions; absorption peaks of Ce3+ are from the 4f→5d(i) (i=1, 2, 3, 4, 5) transitions; absorption peaks of Tb3+ are from the 7F6→4f75d1 (9DJ and 7DJ) transitions. The VUV emission spectra and CIE chromaticity coordinates indicate that both NaSr0.55Ba0.45(PO4):Eu2+ and NaSr0.55Ba0.45(PO4):Ce3+ emit pure blue light. And the NaSr0.55Ba0.45(PO4):Tb3+ emission light is green. In the forth chapter, XRD, FT-IR and SEM tests are also used to make sure the obtained materials are pure Na2CaMg(PO4)2:Eu2+ and Na2CaMg(PO4)2:Ce3+. According to the absorption spectra, the 4f7→4f65d transition of Eu2+, 4f→5d(i) (i=1, 2, 3, 4, 5) transition of Ce3+ and the electron transition in host orthophosphate (from VB to CB) are discussed. The emission spectra and CIE chromaticity coordinates show that both Na2CaMg(PO4)2:Eu2+ and Na2CaMg(PO4)2:Ce3+ have a broad blue emission.In the fifth chapter, the results of XRD, FT-IR and SEM test conform that the pure SrZn2(PO4)2 is prepared. In the excitation spectrum of SrZn2(PO4)2:Eu3+, the electron transition 7F0→5L8,9, 7F0→5G3(5L7), 7F0→5D3, 7F0→5D2 of Eu3+ is obtained in term of a group of peaks. And in the spectrum of SrZn2(PO4)2:Ce3+, the absorption peak of the electron transition between the oxygen ions (O2-) and Ce3+. According to the emission spectra, the emission of SrZn2(PO4)2:Eu3+ is red and the emission of SrZn2(PO4)2:Ce3+ is blue.In the sixth chapter, NaCaPO4:Eu3+ is prepared by Sol-gel method. The SEM photo shows the better shape with narrow size distribution. In excitation spectra, the absorption peaks are duo to the absorption of host orthophosphate in VUV region and the electron transitions of the RE ions. And the position selection of the Eu3+ in NaCaPO4 is discussed according to the excitation spectra. The emission spectra show that NaCaPO4:Eu3+ emits red light, and NaCaPO4:Eu2+ emits green.In this paper, VUV excitation and emission spectra, CIE chromaticity coordinates and decay curve are used to describe the luminescence properties of four RE doped orthphosphates. The mechanisms of the emission are discussed, and the potential value of the application in display and illumination field is investigated.