Preparation And Spectroscopic Characterization Of Oxides And Oxysalts Nanopowders And Transparent Ceramics Doped With Rare Earth Ions

This thesis consists of five chapters. Chapter 1 introduces the background of my work. Chapter 2 to chapter 5 deals with the preparation, characterization and luminescent properties of oxide and oxysalt doped with rare earth ions.In chapter 1, an introduction of rare earth luminescent materials is given at first. Then the basic principles of photoluminescence and properties of rare-earth ions are stated. At last, the knowledge about transparent materials is presented.In chapter 2 to chapter 5, the meaning and development, of the scintillator materials, especially transparent ceramic sintillators, are introduced first. The preparation, characterization and luminescent properties of Lu₂O₃?Eu³⁺, Lu₃Al₅O₁₂:RE³⁺ (LuAG:RE³⁺) and Lu₂SiO₅:Ce³⁺(LSO:Ce³⁺),Lu₂Si₂O₇:Ce³⁺(LPS:Ce³⁺) samples are presented. The contents include two parts:1. Nanocrystalline Lu₂O₃:Eu³⁺ was prepared by co-precipitation method using ammonium hydrogen carbonate (AHC) and ammonium oxalic acid (AOA) as precipitants, respectively. The prepared process, crystal structure and morphology were analyzed by means of TG-DTA, FT-IR, XRD and HRTEM. The resultant powders were sintered into transparent ceramics in vacuum and then in nitrogen without any additive. The surface morphology of the unpolished sintered specimens was characterized using SEM. The effect of different precipitants and doped concentrations on microstructure of the nanopowders and transparency of the ceramics are compared. The powders synthesized by AHC showed better dispersivity and more homogeneous particle size distribution compared with those by AOA, which results in that the ceramic made from AHC has higher transparency compared with that produced from AOA. And the transparency of the ceramics increases with increasing Eu³⁺ concentration.The excitation and emission spectra of Lu₂O₃:Eu³⁺ powders and ceramics were measured at room temperature by using synchrotron radiation as the light source. The typical components of Eu³⁺ excitation and emission spectra appear in all samples. The emission intensity from ⁵D₀ relative to that from ⁵D₁ systematically increases with the increase of Eu content. The relative intensity of the composed bands differs significantly because the effect of different lattice sites on the spectra of ceramics is greater than those of nano-powders. The charge transfer band shift red in small size samples.The fluorescence decay times of all specimens were analyzed. The decay time of the nano-powders shorten with increasing Eu³⁺ content. Luminescence of the ceramics decays faster than the corresponding nanopowders. However, for the sintered ceramics, the decay kinetics remains unchanged within the whole region of investigated concentrations.2. Nanocrystalline LuAG:RE³⁺ (Ce³⁺ or Pr³⁺) was prepared by co-precipitation method. The resultant powders were sintered to translucent ceramics in vacuum and then in nitrogen without any additive. The prepared process, crystal structure and morphology were analyzed by means of TG-IR, FT-IR, XRD, HRTEM and SEM. The results show that the samples crystallized in typical cubic LuAG structure at 900℃. The powders are loosely agglomerated, fairly uniform, and have the near spherical shape with an average particle size of 30 nm at 1000℃.The host absorption and the f-d transition bands all exist in the excitation spectra of LuAG:Ce³⁺ powder and ceramic samples. However, the band induced by Lu_Al antisite defects can only be seen in spectra of ceramic. The emission spectra of ceramics shift towards the red at higher Ce³⁺ concentration; however, those of powders keep unchangeable. YAG:Ce³⁺ nano-powders and ceramics are also synthesized using the same method as LuAG:Ce³⁺, and their luminescent properties are compared with the later.The excitation and emission spectra of LuAG:Pr³⁺ powders and ceramics were measured at room temperature. The emission spectra of LuAG:Pr³⁺ show fast 5d-4f luminescence. The UV emission spectrum of Pr³⁺ shifts by about 150-200 nm towards shorter wavelength with respect to Ce³⁺ in the same host.In addition, LSO:Ce³⁺ and LPS :Ce³⁺ powders were synthesized using sol-gel method. The result of XRD shows that the two samples sintered at 1000℃crystallized in pure LSO and LPS structure. The luminescent properties are measured at room temperature, and the band gap of LPS is calculated.