| Scintillation crystal,as a radiation detection material,has been used in many fields such as safety inspection,space exploration,nuclear medicine,high energy physics and petroleum exploration.With the rapid development of high energy physics experiments,nuclear medicine imaging and other fields,the performance of scintillation crystals has been put forward higher requirements,so the search for a new scintillation crystal material with fast decay has become an important research topic in recent years.In the fast decay mechanisms of scintillation crystals,the core-valence luminescence is one of the effective ways to realize fast scintillation.ABX3 perovskite-type scintillation crystals have the wide band gap due to the large difference in electronegativity between halogen derived valence band and cationic derived conduction band,which makes it easy to realize the corevalence luminescence,so as to meet the fast decay application requirements.At the same time,it has the significant advantages of high density,high light yield,excellent energy resolution and strong anti-irradiation ability.It stands out in the research and development of crystal materials workers at home and abroad and has become a hot research topic at present.In this paper,the major demand of scintillation crystals field as traction,in order to seek scintillation crystals with fast decay,we chose Ce3+-doped CsMgCl3 scintillation crystals as the main research object,using the Bridgman method to grow high quality CsMgCl3:xCe(x=1%,10%,20%)crystals.And we studied systematically the crystal structure,optical properties and scintillation properties.The process conditions and growth parameters required for the growth of CsMgCl3:xCe(x=1%,10%,20%)scintillation crystals were studied in detail for the first time.The crystal cracking problem was successfully overcome by optimizing and improving the growth process conditions in the actual growth process.A Φ 12mm×10mm high quality crystal with completely transparent and no obvious cracks was obtained which could satisfy the subsequent device performance tests.Through first-principles calculation,it has been confirmed that the cell energy was lower and the state was more stable when Ce3+occupied the lattice position of Mg2+.We measured and analyzed the optical properties of the crystals.The optical transmission spectrum of CsMgCl3:Ce crystals showed that they had a short cutoff wavelength,indicating that the crystals had the wide band gap,which provided the conditions for the generation of the core-valence luminescence.The photoluminescence spectrum of the crystals showed that the luminescence was from energy level transition luminescence of Ce3+ions at room temperature,with two distinct emission peaks in the wavelength range of 350-450nm.With the increase of Ce3+-doped concentrations,the luminescence intensity of the samples increased and the emission peaks were blue shift.The temperature-dependent photoluminescence spectrum of CsMgCl3:Ce crystals showed that with the continuous increase of temperature,the activity of lattice phonons became more intense.The process of emitting phonons led to the decrease of lattice energy,the increase of wavelength,slight red shift of emission peaks,band broadening of Ce3+ions.In short,the crystals emission peaks were less dependent on temperature.The partial overlap of emission and excitation bands in the wavelength range from 350nm to 370nm was attributed to the self-absorption effect of the crystals.The photoluminescence decay at room temperature was 35.86ns,which was consistent with the luminescence decay characteristic of Ce3+ions.We measured and analyzed the scintillation properties of the crystals.There were two luminescence mechanisms in CsMgCl3:10%Ce crystals under X-ray excitation.The first luminescence mechanism was the core-valence luminescence,whose emission peak wavelength was 304nm and the scintillation decay was 1.87ns,which accorded with the corevalence luminescence characteristics of CsMgCl3 crystals and was consistent with the fast decay of CsMgCl3 crystals reported in the world.The second luminescence mechanism was the 5d→4f level transition luminescence of Ce3+ ions.The emission peaks wavelength were 382nm and 405nm,and the scintillation decay was 50.16ns.The X-ray steady-state light yield of CsMgCl3:1%Ce crystal was 2510ph/MeV,which was slightly higher than that of CsMgCl3 crystals reported internationally at present. |
