Implementation And Performance Investigations Of Scintillation Properties Of Organic Room-Temperature Phosphorescent Materials

In recent years,X-ray excited organic scintillators have attracted attention for their great potential in radiation detection,security screening,biomedical imaging and photodynamic therapy due to their abundant resource availability,high mechanical flexibility,ease of processing and large area fabrication.However,most of the organic scintillators reported so far are fluorescent molecules,where only 25%of the excitons are available for radioluminescence after electron-hole complexation under X-ray irradiation.According to spin quantum statistical theory,most of the triplet excitons（～75%）are wasted due to the dark state nature of triplet excitons in pure organic molecules,which also greatly affects the development of organic scintillators.Organic room-temperature phosphorescent（RTP）materials,due to their bright triplet exciton properties,would theoretically lead to a significant increase in exciton utilisation,resulting in good radioluminescence,however,organic phosphorescent scintillators are still at an exploratory stage,with weak X-ray capture capabilities limiting their development,and little research has been carried out on molecular design strategies and the link between structure and performance.Therefore,this thesis is based on organic room temperature phosphorescent materials,around the key issue of how to obtain efficient radioluminescence and modulate performance enhancements,a series of organic phosphorescent scintillators are synthesized and prepared,and a series of structural characterization and performance studies are conducted on the materials,the specific work are as follows:（1）The presence of high atomic number elements is important for enhancing the X-ray absorbance and radioluminescence of the scintillators.In order to achieve good radioluminescence performance,a series of heavy-atom iodine-modified pure organic molecules based on theβ-diketodifluoroboron structure are obtained in this chapter through rational molecular design,using the heavy-atom effect to promote the ISC process and enhance the absorption capacity for X-rays,while endowing them with good H-aggregation properties to show RTP emission,exhibiting a lifetime of up to 196 ms and a quantum efficiency of 12.99%.By changing the site of the iodine atom on the benzene ring,the materials exhibit different radioluminescence properties,and under X-ray irradiation,the different molecular stacking properties of the compounds allow the isomeric radioluminescence colors to be tuned from blue to white and yellow,which providing a new research idea for further development of the radioluminescence field and a reliable guide for subsequent applications.（2）The low efficiency of organic scintillators limits their use in medical,radiation detection and other applications.A series of heavy-atom-free pure organic phosphorescent scintillators are designed and prepared,which showed a lifetime of up to 682 ms and a photoluminescence quantum efficiency of 65.8%and exhibited good scintillation properties under X-ray irradiation.Experiments and studies have shown that the charge transfer（CT）properties provide good response properties to X-rays and that the presence of the H-aggregate structure confers a long afterglow emission from the scintillators.Also the ISC process is enhanced by triple-mode（TADF、phosphorescence and afterglow）emission,accompanied by a shift from spin-barred emission in the trilinear state to spin-allowed single-line emission,improving the utilisation of bright trilinear excitons.Under X-ray irradiation,the Cz PADB scintillators exhibit enhanced radioluminescence properties,as well as a radiation detection limit as low as 110 n Gys^-1 and excellent stability,which providing a new research strategy for the subsequent development and design of efficient and stable organic phosphorescent scintillators.（3）The poor water solubility of organic scintillators limits their application in some areas such as bioimaging.In this chapter,the new metal-organic vesicle hollow nanoparticles were obtained by a rational self-assembly method and their structure was demonstrated by FT-IR,AFM,TEM and other tests.The solution shows phosphorescence emission with an accompanying phosphorescence emission lifetime of 4.3 ms due to the organic RTP molecules being firmly confined in the vesicle membrane.The solution also has good absorption and response to X-rays due to the introduction of metallic elements,which providing a new design strategy for further broadening the use of organic phosphorescent scintillators for X-ray bioluminescence imaging and drug delivery applications.