The Study On Preparation And Scintillation Properties Of Sm³⁺/Cr³⁺ Co-doped GdAlO₃ X-ray Phosphors

X-ray phosphor is a luminescent material that can converts high-energy X-rays into low-energy visible light,which has a broad application prospect in medical,industrial and biological fields.Especially it plays a very important role in the DR imaging system.Currently,mature and commercially available X-ray phosphors have unfavorable factors such as high cost,poor stability,complex preparation process,and environmental pollution,etc,which are difficult to meet many requirements of ideal X-ray phosphors at the same time.In order to meet the demand for ideal phosphors in recent years,excepting for improving the existing X-ray phosphors,it is also necessary to explore red X-ray phosphors with excellent comprehensive performance and are well matched to the highest sensitivity range of the photodetector.In this dissertation,Sm³⁺single-doped GdAlO₃ and Sm³⁺,Cr³⁺co-doped GdAlO₃ novel X-ray phosphors were prepared by high-temperature solid-phase method,and their optical properties and scintillation performance were investigated.Firstly,GdAlO₃:Sm³⁺X-ray phosphors with micron size（1.95μm）were prepared by high-temperature solid-phase method.The peaks of the fluorescence spectra under near-ultraviolet（406 nm）excitation and X-ray excitation were located at 563 nm,601 nm,646 nm,and 704 nm,both of which were characteristic emission peaks of Sm³⁺.The pattern of variation of emission intensity with concentration was consistent in both spectra（with the increase of concentration,the emission intensity showed a trend of first increasing and then decreasing）,where the GdAlO₃:0.7%Sm³⁺phosphor had the best luminescence.Secondly,the GdAlO₃:0.7%Sm³⁺sample was tested by temperature-variable emission spectrum,the emission intensity of the sample at high temperature（473 K）was equivalent to 60%of that at room temperature（293 K）,which had good thermal stability.In the fluorescence decay curve test,the lifetime of the sample was approximately 708 ns,which was shorter than some established and commercially available X-ray phosphors.In addition,GdAlO₃:0.7%Sm³⁺sample rounds under X-ray irradiation showed bright orange-red light,indicating that GdAlO₃:0.7%Sm³⁺X-ray phosphor has potential application prospects in DR imaging.Based on the above optimal doping concentration of Sm³⁺,we prepared GdAlO₃:0.7%Sm³⁺,y%Cr³⁺X-ray phosphors by high-temperature solid-state method（y=0.3,0.5,0.7,0.9,1.1）.The particle sizes were around 2.01-2.07μm,indicating that the doping with different concentrations of Cr³⁺did not have much effect on the particle size of the samples.The photoluminescence spectra showed that GdAlO₃:0.7%Sm³⁺,0.7%Cr³⁺samples had the best luminescence.In addition,the energy transfer phenomenon between Sm³⁺and Cr³⁺was verified from several angles(overlapping emission spectra of Sm³⁺and excitation spectra of Cr³⁺,lifetime changes of two doped ions,and spectral analysis of co doped samples),and the energy transfer mechanism between Sm³⁺and Cr³⁺was determined to be a quadrupole-quadrupole interaction.In the variable-temperature emission spectrum,when the temperature was at high temperature（473 K）,the luminous intensity was 70%of that at room temperature.In addition,comparing the luminescence and afterglow characteristics of the two doping modes under X-ray excitation,the luminescence of GdAlO₃:0.7%Sm³⁺,0.7%Cr³⁺X-ray phosphors was nearly doubled compared with that of GdAlO₃:0.7%Sm³⁺X-ray phosphors,and the afterglow initial intensity was reduced by about one order of magnitude,and the position of the main peak was shifted from the previous 601 nm to 725 nm.Therefore,GdAlO₃:Sm³⁺,Cr³⁺co-doped samples were more suitable to match the highest sensitivity response range of Si-CCD.Finally,the GdAlO₃:0.7%Sm³⁺,0.7%Cr³⁺co-doped samples with optimal performance were mixed with PMMA（polymethyl methacrylate）to make circular films for imaging under X-ray irradiation,and the GdAlO₃:0.7%Sm³⁺,0.7%Cr³⁺X-ray phosphors exhibited a high spatial resolution of about 3.4 lp/mm.In the fluorescence decay graph,its lifetime is shorter than some phosphors that have been used or are being developed for medical imaging(e.g.Cs I:Tl⁺,Gd₂O₂S:Pr³⁺/Ce³⁺,Lu₂O₃:Eu³⁺).Its advantages are fast response speed,improved imaging time resolution,and largely avoided ghost phenomenon caused by continuous scanning.The above experimental results show that GdAlO₃:Sm³⁺,Cr³⁺X-ray phosphors have great application value in modern medical X-ray imaging.At the same time,it provides a new idea in the direction of developing new X-ray phosphors.