Synthesis,structure And Luminescence Characteristics Of Luminescent Materials With Oxygen Vacancies And Asymmetrical Coordination Geometries

Inorganic solid-state luminescent materials,as a kind of important functional materials,have been widely used in lighting,industrial display,daily life,biomarkers in medical research,security and military fields due to their unique advantages.Although more and more inorganic solid-state luminescent materials have been developed,there is still a lack of rational design concepts and effective research methods,which seriously restricts the speed of development and practical application of new luminescent materials.In recent years,the construction and adjustment of microstructures(defect,atomic and electronic structures)is an effective strategy to realize the excellent optical properties of inorganic solid-state luminescent materials.In this context,we constructed and adjusted the microstructure from the perspectives of defects and coordination environment,thereby designing luminescent materials with oxygen vacancies and asymmetrical coordination geometries.Systematic experimental and quantitative characterization,revealed the relationship between microstructure and macroscopic luminescence properties of these materials,and on this basis,their luminescent mechanisms were proposed.The main research contents and results are as follows:(1)We synthesized the oxygen-deficient Aurivillius phase,Bi2.14Sr0.75Ta2O9-x powder by a solid-state reaction method and further studied its defect structure and luminescence properties.It was found that the ultrabroad near infrared(NIR)luminescence center exists in defective[Bi1.95O2-x]layers.Experimental characterization of Bi2.14Sr0.75Ta2O9-x,combined with theoretical calculations,suggested the V(?)3 and V"’Bi2V(?)3V"’Bi2 defects are predominant in[Bi1.95O2-x]layers,and the NIR luminescence originates from the local energy states induced by defects in[Bi1.95O2-x]layers.In addition,we demonstrated that this finding can be applied to a variety of Aurivillius phases with defective[Bi2O2]layers.This work shows the importance of defects located in[Bi2O2]layers in endowing Aurivillius ferroelectrics with ultrabroad luminescence properties,which provides a new strategy for further coupling of its ferroelectric property with NIR luminescence.(2)First-principles calculations were employed to identify the thermodynamic chargetransition levels of different defect states in LaPO4 host,which help us to propose the hypothesis that some structural defects could function as electron trap centers for afterglow,and ultraviolet C(UVC)-afterglow Pr3+-doped LaPO4 powders with defects were synthesized by a solid-state reaction method.The as-synthesized powders were further treated through topochemical reactions and defect structure and luminescence properties were investigated before and after the treatment.We found that the species and concentrations of structural defects could be rationally tuned through this reaction,which leads to discovery of the persistent phosphors featuring UVC afterglow with a lasting time of over 2 h.Based on the experiment results,we confirmed that oxygen divacancies could enhance room-temperature afterglow and the corresponding charge carrier trappingdetrapping process was closely related to the dynamic change of phosphorus-oxygen radicals,thereby proposing a radical-involved afterglow mechanism.We finally demonstrated that the design concept and research method could be extended to other phosphorus oxygen systems with defects.This work creatively proposes that theory-guided defect tuning through topochemical reactions can be used to accelerate discovery of long persistent phosphors,which facilitates the design of afterglow materials rises from the traditional trial and error method to the rational concept.(3)We successfully synthesized layered BaBiO2.5 powder,the most representative derivative of perovskite BaBiO3,by a non-topotactic phase transformation and further investigated its coordination geometry and luminescence properties.It was found that Bi-O bonds demonstrate unusual features showing one ionic bond and three covalent bonds,which results in an asymmetric Bi coordination geometry with the seesaw type.Luminescence spectral analysis revealed that this peculiar structure shows near-infrared(NIR)luminescence never seen in any Bi-containing system reported previously.Experimental results,coupled with quantum chemistry calculations,lead us to propose the excitonic nature of NIR emission.The strategy of designing new Bi-containing luminescent materials from the perspective of coordination environment is expected to prompt the discovery of more luminescent materials with excellent properties.