Preparation And Optical Properties Of NaGdSiO₄:Eu³⁺ Scintillator

In the past decades,single-crystal rare earth silicate scintillator detectors have demonstrated great potential for applications in radiation detection fields including high-energy physics,nuclear medicine,oil logging,and security inspection.However,complex preparation techniques and high production cost limit its further developments.Recently,composite scintillators composed of nanocrystals（NCs）and polymers have received increasing attention in the field of radiograph due to their low cost and good imaging quality.However,the small size of nanocrystal scintillators calls for higher stopping power and light yield.To deposit high-energy radiation effectively and achieve high-quality radiography with wide dynamic range and high resolution,it is of great theoretical significance and application value to develop small-size scintillator materials with high density and high effective atomic number.In this work,a novel routewas designed to prepare Na Gd₉Si₆O₂₆（NGSO）submicron crystals,a rare earth silicate material with high density and high effective atomic number.The crystal growth mechanism of this material was deeply discussed.The influence of Eu³⁺doping amount on the crystal structure and the luminescent properties was throughly investigated.On the basis,the method of preparing PDMS-based flexible X-ray composite scintillator film loaded with NGSO:Eu³⁺submicron crystals was developed.The X-ray imaging properties of the composite scintillator were comprehensively investigated.The main research results are as follows:1.In combination with a Na OH etching process,the effect of the temperature on phase structure and size of NGSO crystals was investigated during the solid state reactions with Na GdF₄@SiO₂ as precursors.Benefiting from the higher reactivity of Na GdF₄@SiO₂ structures,the NGSO phases were found to form at～550°C,which was much lower than the conventional sintering temperature（>1000°C）in the bulk size reactions.In the reaction temperature range of 600-900°C,the reconstruction and fusion of NGSO grains can be effectively inhibited by shortening the reaction time,and the crystal size tends to increase with the rise of reaction temperature.NGSO submicron crystals with an average size of～550 nm were successfully obtained at 600°C.2.Utilizing Eu³⁺ions as the luminescent centers with red emissions,the effect of its doping level on the phase structure and luminescent properties of NGSO crystals was systematically investigated.It was show that under high pressure in etching process,the increasing Eu³⁺doping induced phase changes from the initial hexagonal-30 phase（JCPDS#30-1264）to the intermediate cubic-28 phase（JCPDS#28-1190）,and then to the final cubic-35 phase（JCPDS#35-0012）mainly due to the difference in bond energy between Eu-O and Gd-O.In the 80 mol%doped NGSO:Eu³⁺,the dominant 28-1190phase content possesses the larger distance between the rare earth（RE）sites,which can significantly weaken the concentration quenching caused by exchange interactions.Therefore,it exhibits the maximum luminous intensity under both ultraviolet and X-ray excitation,and a light yield of 2214 photons/Me V for X-ray radiation.3.Based on the above work,a flexible X-ray imaging film was prepared by loading NGSO:80Eu³⁺submicron crystals into PDMS polymer,and the optical and radiographic properties of the film were systematically investigated.Compared with the PDMS film loaded with NGSO microcrystals prepared by high-temperature solid-state sintering,the NGSO:Eu³⁺submicron crystal/PDMS composite film exhibited higher transparency and spatial resolutions:an improved transmittance from 53%to65%at 614 nm;and an increase in spatial resolution by 7%for MTF=2.A good radiation hardness was revealed in the radiation stability test with 80.2%of the original intensity maintained even after a continuous irradiation with high-dose rate X-rays for 80 minutes.