Vacuum-ultraviolet Spectroscopy And Luminescence Properties Of Phosphates Doped With Ce³⁺ Or Pr³⁺

In recent years,with the development of rare earth doped vacuum ultraviolet fluorescent materials,they have been widely used in medical imaging,radiation detection,high-energy physics,cosmic dark matter detection and other fields.However,there are still some disadvantages,such as low light yield,slow lifetimes,poor thermal stability and low energy resolution.Thus,more and more attention have been paid to the exploration of new vacuum ultraviolet fluorescent materials.In addition,the rapid development of synchrotron radiation vacuum ultraviolet experiment provides a good experimental condition for the study of high energy excited state of rare earth ions.Among many rare earth materials,phosphate and borate have the prominent advantages,that are strong rare earth solubility,good chemical stability,high luminous efficiency,good thermal stability,low synthesis temperature and so on,and many scientific research workers attach importance to them.Therefore,we doped Ce³⁺and Pr³⁺in phosphate.The thesis is divided into following sections:（1）Sr₉Lu（PO₄）₇ doped with Ce³⁺was synthesized by means of conventional solid-state reaction.The structure of the sample was characterized by XRD,and it was found that the synthesized sample contained 6%Sr₃Lu（PO₄）₃.However,it could be ignored because of few impurities that had little effect on the spectral properties.It was found that Ce³⁺mainly occupy two different positions of Sr²⁺,deriving from the UV-VUV spectrum and X-ray excitation spectrum of the samples.The lowest 5d energy level positions of Ce（1）and Ce（2）were obtained at30079 cm^-1 and 32417 cm^-1,and there is effective energy transfer from the host to the luminescence center.The rule of lifetimme and the effect of temperature on fluorescence life were identified by testing the attenuation curve of the sample.Ce（1）and Ce（2）have excellent thermal stability through testing the attenuation curve of the samples.（2）Sr₉Lu（PO₄）₇ doped with Pr³⁺was synthesized by means of conventional solid-state reaction.Pr³⁺occupies only the Sr²⁺site and not the Lu³⁺lattice in this matrix.Through the analysis of the spectrogram,it was found that the peak of excitation band Pr³⁺were 5.56 eV（223 nm）.Emission spectra reveal that there is not only the emission of Pr³⁺but also the defective emission in the sample,and there is an effective energy transfer from the host to Pr³⁺.Decay time of the Sr₉Lu（PO₄）₇:0.5%Pr³⁺upon 270 nm is about 17.6±0.1ns,with short life time and good thermal stability.（3）Ba₃La（PO₄）₃ doped with Ce³⁺was synthesized by means of conventional solid-state reaction.It is found that La/Ba lattice is replaced by Ce³⁺of the sample,and Ce（1）and Ce（2）occupy the two kinds of lattice by analyzing emission spectrum and decay time.Emission spectrum reveals the highly transfer efficiency from the host to the luminescence center.The lowest 5d energy level position of Ce³⁺in BLP was about 31772 cm^-1.The decay life of Ce（2）is always maintained at31ns with temperature ranging from 78 K-500 K,that have excellent thermal stability.Ce（1）always maintains the decay time of about 51ns under 300 K,but there was an apparent decrease in life time when temperature higher than 300 K,that due to temperature quenching.（4）Ba₃La（PO₄）₃ doped with Pr³⁺was synthesized by means of conventional solid-state reaction.The X-ray diffraction and emission spectra reveal Pr³⁺only occupies one lattice of La³⁺.According to the analysis of excitation spectrum and emission spectrum,the lowest energy level position of 4f^n-15d of Pr³⁺is about 44029 cm^-1.The energy transfer efficiency from substrate to Pr³⁺is higher at low temperature,but the energy transfer efficiency is greatly reduced at room temperature.Doping5.0%Pr³⁺has a higher luminescence intensity than 1.0%Pr³⁺,and both their life remain around 16ns without concentration quenching.