Structure And Luminescence Properties Of Cerium-doped LuAG/Al₂O₃and (Lu_2/3Gd_1/3) AG/Al₂O₃eutectic Grown By Micro-pulldown Method

Rare earth elements outer electronic structures are basically the same,and some rare earth elements inner electrons have similar energies.Therefore,they have potential properties in optical,electricity and magnetic,which have a wide uses in the reserach,production.Since the trivalent rare earth cerium ion(Ce³⁺)has a simple electronic configuration and its 5d?4f transitions allow for parity and spin allowed transitions,which can produce higher fluorescence quantum efficiency and shorter fluorescence lifetime?nanoseconds?.Lu₃Al₅O₁₂?LuAG?crystals have a high density??=6.67 g/cm³?and a large effective atomic number(Z_eff=63),so the Ce³⁺:LuAG crystals have good scintillation properties.Taking into account the light scattering of the scintillation single crystal in the guide-light and the physical processing limit for processing to form a tiny pixel for imaging,which hardly to improve the imaging resolution.We combine the Lu₂O₃-Al₂O₃ binary phase diagram,expected to prepare an ordered optical structure Ce³⁺:LuAG/Al₂O₃ eutectic to solve the problem.The structure,composition and luminescence properties of Ce³⁺:?Lu,Gd?AG/Al₂O₃ system eutectic were studied by X-ray powder diffractometry,fluorescence spectroscopy,field emission scanning electron microscopy?SEM?which equipped with energy dispersive spectroscopy,X-ray excitation spectroscopy,and thermo-luminescence spectroscopy for a detailed characterization.The first chapter summarizes the research background of this work,and briefly summarizes and reviews the research progress of the scintillation eutectic.Combining related research status,systematically elaborated the basis for this topic and research content.In Chapter 2,the working principle and structure of the micro-pulling-down technology are described in detail,and the precursor synthesis and crystal growth program are described in detail.The characterization methods and specific instrument parameters used in this paper are described in detail.In the third chapter,the growth of Ce³⁺:LuAG/Al₂O₃ eutectic and the effects of doping concentration and pull-down speed on the microstructure and luminescence properties of the eutectic were studied.XRD results showed that the eutectic consisted of two phases of Lu₃Al₅O₁₂ and Al₂O₃,without the presence of other phases.The eutectic microstructure shows that the eutectic exhibits a typical“Chinese Script”structure perpendicular to the growth direction,and exhibits an orderly two-phase distribution in the direction of parallel growth.The energy dispersive spectrum and elemental mapping results clearly showed that the composition and distribution of the two phases.Fluorescence spectrum analysis showed that the best doping concentration of Ce was 1.0 at%,and the pull-down speed reached 1.7mm/min eutectic showed the strongest emission,which was consistent with the orderly structure of the sample at the microscopic level.In the fourth chapter,the growth of Ce³⁺:(Lu_2/3Gd_1/3)AG/Al₂O₃ and the effect of pull-down speed on the microstructure and optical properties of the eutectic were studied.The eutectic microstructure shows that the eutectic exhibits a"Window-Flower"structure in the both vertical and parallel growth directions and is arranged in an orderly manner.The effect of different pull-down speed on the emission intensity of the sample is not clear.In the fifth chapter,we mainly studied the difference of fluorescence and thermoluminescence properties,under the same experimental conditions with the same doping concentration of single crystal and eutectic.The optical properties shows that the emission of the two groups of specimens excited by ultraviolet light tends to be consistent with the results of X-ray excitation.The change trend from strong to weak is eutectic,single crystal.The thermoluminescence spectra of the three groups of specimens showed that the defects of the specimens were mainly distributed in the low temperature region?100-275 K?and were dominated by shallow electronic defects.Among them,the eutectic had the most widely distributed defects?the area of the peak is the largest?,followed by the single crystal.