Preparation And Scintillation Properties Of Pr³⁺/Bi³⁺ Co-Doped LaAlO₃ X-Ray Phosphors

X-ray phosphors can effectively convert high-energy ionising radiation（X-rays etc.）into low-energy ionising radiation（UV-Vis）and are widely used in medical diagnostics,dose detection,and other applications.Currently,commercial phosphors are mainly based on halides doped with rare earth ions.Halide-based X-ray phosphors have good luminescence properties under X-ray irradiation,but their structural characteristics make them physicochemically unstable,susceptible to deliquescence,and polluting the environment.Therefore,it is a hot issue to develop X-ray phosphors with good stability,a simple synthesis method,friendly to the environment,and excellent luminescence performance.In this thesis,LaAlO₃:Pr³⁺X-ray phosphors with different Pr³⁺doping concentrations were successfully prepared by high-temperature solid phase calcination at 1500℃ for 3 h.The average size of the particles was 2.44μm.The emission spectra under optical excitation at 449 nm and X-ray excitation were identical,both of which could be observed at 490 nm and were attributed to The strongest blue-green emission peak at 490 nm,attributed to the ³P₀→³H₄transition,and the red emission peak at 611 nm,attributed to the ¹D₂→³H₄transition,were observed.It is discussed that the red emission of the sample is due to the relative position of the charge transport（IVCT）states leading to a burst at the ³P₀ energy level,while enhancing the red emission at the ¹D₂ energy level.As the concentration of Pr³⁺ions increases,the photoluminescence intensity and the luminescence intensity under X-ray excitation tend to increase and then decrease,reaching a maximum at a Pr³⁺ion doping concentration of 0.9%.The fluorescence decay analysis of the LaAlO₃:Pr³⁺sample was carried out and the average decay time was calculated to be 20μs.In addition,the variable temperature spectra of the samples were tested and the emission intensity at 611 nm was maintained at 49%of room temperature when the temperature reached 473 K.The optimal sample,LaAlO₃:0.9%Pr³⁺,was then subjected to X-rays to photograph its luminescence,which can be seen as a bright red-orange colour with CIE colour coordinates of（0.60,0.40）.In addition,the results of the afterglow test under X-ray excitation show that the sample has no afterglow under X-ray.All these results indicate that LaAlO₃:Pr³⁺X-ray phosphors have potential applications in X-ray imaging.Secondly,in order to improve the luminescence intensity and optimise the performance of the LaAlO₃:x%Pr³⁺X-ray phosphor,samples of LaAlO₃:Pr³⁺X-ray phosphor doped with different concentrations of Bi³⁺ions were prepared by high-temperature solid phase method.The red light emission peak at 611 nm was still observed for the phosphor under optical excitation at 254 nm and X-ray excitation,which matched the highly sensitive sensing wavelength of the CCD,and it gradually increased with increasing Bi³⁺ion doping concentration and reached the strongest at 1.1%Bi³⁺ion concentration.Next,the emission spectra of LaAlO₃:Bi³⁺and the absorption spectra of LaAlO₃:Pr³⁺were tested separately.It can be seen that the emission peak of Bi³⁺ions at 366 nm and the absorption peak of Pr³⁺ions at 358 nm overlap,indicating that there is an effective resonance energy transfer from Bi³⁺ions to Pr³⁺ions.The results of the fluorescence decay curve also show that the fluorescence decay time of Pr³⁺ions increases from 20μs to 28μs as the doping concentration of Bi³⁺ions increases,which can also verify the energy transfer from Bi³⁺ions to Pr³⁺ions.In addition,thermal stability tests were carried out on LaAlO₃:0.9%Pr³⁺,1.1%Bi³⁺phosphors,and it was observed that the intensity of the emission peak at 611 nm remained at around 68%of the initial temperature when the temperature was increased to 473 K.In addition,pictures were taken of the luminescence of the wafer samples under X-ray irradiation for a range of concentrations and it was observed that the brightness of the samples increased significantly with increasing Bi³⁺ion doping concentration and was brightest at a concentration of 1.1%.And there is no afterglow under X-ray for all concentrations of the samples.Finally,the best samples of LaAlO₃:0.9%Pr³⁺,1.1%Bi³⁺were made into thin films and X-ray imaging was carried out based on wire-to-card,which showed a resolution of 2.50 lp/mm.This indicates that the samples have a high resolution under X-ray irradiation.In summary,LaAlO₃:Pr³⁺,Bi³⁺X-ray phosphors have potential applications in the field of medical imaging.