| New scintillation crystal SrI2:Eu offers a high light output, low theoretical energy resolution and excellent light output proportionality, is very sensitive to X-ray and γ-ray, and applies to security detectors and nuclear radiation detection.In this thesis, it prepares SrI2and SrI2:Eu crystal by vertical Bridgman technique under vacuum condition, finds the growth process parameters suitable for SrI2and SrI2:Eu crystal, obtains the macroscopic complete, transparent crystals, the size of SrI2crystal and SrI2:Eu crystal are Φ10×70mm and20×10×2mm respectively. Studies the coloration phenomenon of the crystal, and performance characterization through the test that UV fluorescence spectra, X-ray excitation emission spectra and UV fluorescence lifetime, etc, finds that SrI2:Eu crystal has high luminescent intensity, a long decay time and the radiation trap effect serious.In this thesis, the mainly research work are including the following aspects:(1) The thermal analysis is used to study that the melting point of SrI2and SrI2:Eu crystals are535.6℃and536.4℃, and the freezing point of SrI2and SrI2:Eu crystals are476.5℃and481.1℃, respectively, growth SrI2and SrI2:Eu crystals successful by Bridgman technique under vacuum condition. It finds a suitable growth process parameters by repeated experiment:the temperature of the high temperature zone is sets to610℃, the temperature gradient of the temperature gradient zone is maintained at15-20℃/cm, the crucible descent rate is0.804mm/h, and cooling rate is10-15℃/h. And it studies the relationship between the growth process parameters and crystal defects, finds that the ways to eliminate defects:the cracks can be avoided by improving the insulation structure, slowing the rate of descent and cooling. Bubbles can be avoided by increasing the holding time and slowing the rate of descent.(2) Srl2crystal testes UV fluorescence spectrum and X-ray excitation emission spectrum, finds that its emitting comes from the trap exciton emission, the fluorescence decay curve can be fitting for two components, l1=113.89ns and l2=329.54ns, consistent with more than one emitting pathway in UV emission spectrum. The X-ray excitation spectrum of SrI2:Eu crystal is similar with its the UV emission spectrum which has a broadband around435nm, corresponding to the Eu2+ ions5dâ†'4f transition. The fluorescence decay curve of SrI2:Eu crystal can be fitting for i=998.48ns, it is caused by Eu2+ions emission, this value is better than the decay time that reported in the international. The X-ray excited emission spectra were measured under the same conditions, it finds that the luminescent intensity of SrI2:Eu crystal is much higher than CsI:T1scintillation crystal, fifteen as much as the luminescent intensity of CsI:T1crystal.(3) It studies the radiation trap effect of SrI2:Eu crystal, the emission spectrum of SrI2:Eu crystal has red shift and decay time extends with increase of radiation trap effect, and reduces the luminous efficiency. The segregation coefficient of Eu2+ions is1.0706, he concentration effect and radiation trap effect impact the inhomogeneity of performance in SrI2:Eu crystal. It can improve the utilization rate of crystal by increase Eu2+ions concentration within the range that cant not cause concentration quenching.(4)It studies the phenomenon of coloring crystal, test results:the emission peak of the emission spectrum is at590nm, compares with the normal crystal, the emission peak occurs obvious red shift. The fluorescence decay curve can be fitting for i=752.3142ns, it is less than the decay time of the normal crystal. This phenomenon may be cause by the trace oxygen when sealing the quartz crucible, it changes the local crystal field environment of Eu2+ion, results the abnormal emitting. |
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