Design, Preparation And Properties Of New Near-infrared Long Persistent Phosphorescent Materials

Due to the rapid development of social economic and the continuous improvement of people living standards,emerging technologies and applications put forward higher requirements and expectations for the development of materials.In recent years,near-infrared?NIR?long persistent phosphorescent materials have received great concerns on bioimaging,disease detection and treatment research.Owing to its unique advantages of excitation-emission isolation,high signal-noise ratio,wide field imaging,etc.,NIR long persistent phosphorescent material is an excellent candidate for new biomarker material that is expected to meet the requirements of high quality,high precision and high resolution imaging.However,there are many problems need to be improved:firstly,NIR phosphorescent activators are rare as well as proper host material;secondly,the emission wavelength of NIR long persistent phosphorescent materials are mostly limited in the first biologically transparent window;last but not least,the long-term accumulation in in vivo hampers the possibility of clinical application.Therefore,in view of the above problems,it is of great practical significance to carry out the research and exploration on the design and development of new NIR long persistent phosphorescent materials.The dissertation is composed of five chapters,which focus on exploring new ideas and new methods for the design and synthesis of new NIR long persistent phosphorescent materials from three directions:new material system,new luminous band and new breakthrough of application.The first chapter introduces the history,classification and existing problems of long persistent phosphorescent materials,and emphasizes the significance of this research issue.The second chapter introduces the preparation and characterization methods of the samples.The third,fourth and fifth chapters provide the detailed investigations,discussions and results of new NIR long persistent phosphorescent materials.The specific research results are as follows:?1?A novel NIR long persistent phosphorescent material was successfully designed and synthesized,suggesting a strategy of element substitution to tune the operational waveband and emission intensity.In ZnGa₂O₄:Ni²⁺and Zn_1+ySn_yGa_2-2yO₄:Ni²⁺phosphors,the broad NIR afterglow band around 1000-1600 nm is assigned to ³T₂?³F??³A₂?³F?transition of Ni²⁺ions.We demonstrated that the long persistent phosphorescence in Zn_1+ySn_yGa_2-2yO₄:Ni²⁺with the tunable emission band peaking from 1270 to 1430 nm is tailored by controlling local crystal field around the Ni²⁺ions,which allows extensive control of emission band in the second biologically transparent window.Moreover,the electron paramagnetic resonance spectra show the dynamic change of carriers in the afterglow process.?2?Tm³⁺-doped CaS NIR long persistent phosphorescent phosphors were prepared,which exhibit dual biologically transparent window emissions?700-830 nm;1200-1250 nm?and long afterglow duration.The dominated NIR afterglow peaks are around at 700 nm,810nm and 1224 nm,respectively,which are derived from ³F_2,3?³H₆,³H₄?³H₆/¹G₄?³H₅ and³H₅?³H₆ transitions of Tm³⁺ions.Furthermore,a methodology of customizing afterglow bands via the bandgap tailoring in Ln³⁺-doped NIR long persistent phosphorescent material is proposed,since the spectroscopic data imply that CaS host awakens the comatose NIR afterglow of Tm³⁺centers due to energy-level annihilation in narrow bandgap host,strongly guiding Tm³⁺4f-4f low-energy photonic transition.?3?Taking advantage of the hydrolysis occurring in CaS:Tm³⁺inorganic nanocrystals,CaS:Tm³⁺@SiO₂ NIR long persistent phosphorescent nanoparticles were designed and synthesized as a novel NIR long persistent phosphorescent material with in vivo degradation ability.By comparing the variation of the NIR afterglow decay between CaS:Tm³⁺and CaS:Tm³⁺@SiO₂ in the phosphate-buffered saline,it is demonstrated that the surface coating of mesoporous silica layer can effectively improve the stability and the NIR afterglow performance of CaS:Tm³⁺nanoparticles in aqueous environment.In addition,no significant cytotoxicity can be observed via the MTT assay,indicating CaS:Tm³⁺@SiO₂ as well as the products of hydrolysis are not harmful.It is suggested that these concepts and materials may offer an epoch-making approach for exploring in vivo biodegradable NIR long persistent phosphorescent materials,providing a wide range of potentially practical materials for in the fields of clinical bio-medical imaging,drug delivery,and theranostics.