Design, Preparationand Properties Of New-Wavelength NIR Long Phosphorescent Phosphors

Persistent luminescence（also called afterglow） can be defined as the emission, having the a afterglow time ranging from several minutes to several hours after the removal of excitation sources including visible light or ultraviolet light. Long persistentphosphor is a kind of valuable and environmental friendly material, the works on long phosphorescent phosphors（LPPs） on the early stage were in pursuit of applications in decorations, displays, emergency sign, and illumination in darkness. Later on, the applications of LPPs are gradually extended to other important areas, such asinformation storage, detection of radiation, photocatalytic degradation and optical bio-imaging. Because the nanoparticles withNIR persistent luminescence have a long NIR afterglow time, there is no need to offer the in situ excitation during the biomedical imaging. They not only can completely avoid tissue autofluorescence, light scattering and phototoxicity during the optical excitation, but also have deeper tissue penetration, because their emission bandslocate in thebiological window. Therefore, the research issueabout NIR LPPs is very important.The dissertation is composed of five chapters. Chapter 1 introduces the history of long persistent phosphors, Chapter 2 introduces the sample preparation and measurements. Chapter 3/4/5 provide the detailed investigations on new-wavelength near infrared LPPs. The main research results include:（1） Anovel “Top-down”strategywas presented to design thelong phosphorescent phosphors in the second biological transparency windowvia energy transfer. Inherence in thisapproach to material design involved aningenious engineering for hybridizing the coordination networks of hosts, tailoring the topochemicalconfiguration of dopants, and bridging a cascaded tunnel for transferring the persistent energy from traps, to sensitizers and then to acceptors. Another significanceof this endeavour wasto highlight a rationalscheme for functionally important hosts and dopants, Cr/Nd co-doped Zn1-x CaxGa2O4 solid solutions. Suchsolid-solutionwasemployed as an optimizedhost to take advantage of its characteristic trap site level to establishan electron reservoir and network parameters for the precipitation of activators Nd³⁺ and Cr³⁺. The results revealed that the strategy employed here hadthe great potential, as well as openednew opportunities for futurenew-wavelength, NIR phosphorescent phosphors fabrication with many potential multifunctional bio-imaging applications.（2） NIR Bi²⁺-doped ASnO3（A=Ca, Sn） long-persistence phosphors were prepared by solid state reaction witha broad emission（700-900 nm）and long afterglow duration.In the context of materials selection, these phosphor systems successfully avoided the existing ubiquitous reliance on Cr³⁺,Mn2+ and Mn4+-doped phosphorescent phosphors. Multifariously structural and spectroscopic characteristicsincluding X-ray diffraction and rietveld refinement, scanning electron microscope, X-ray photoelectron spectra as well as photoluminescence, long persistent phosphorescencespectra and thermo-luminescence curves were systematically carried out to clarify the mechanism of the long-persistent phosphorescence. The demonstrated NIR imaging permited a potential of an enablinglong-term,real-time and reliable visualization of deep tissues. This new indicator might open the possibility of selecting Bi²⁺ as the desirable optical center to fabricate new-wavelength, low-cost, NIR phosphorescent phosphors withmany potential multifunctional bio-imaging applications.（3） We reported a simple approach to activate the NIR long persistent phosphorescence via redox reaction. NIR long persistent phosphorescencewas observed in a Cr-doped non-gallate phosphor, i.e. CaTiO3:Cr with perovskite structure through heat treatment in reducing atmosphere, while no such phenomenon wasobservedin the sample with same composition and heat treated in air. The mechanism for activation of Cr-related long persistent phosphorescence wasdiscussed. The designed phosphors successfully breakthe monopoly of the ordinary Cr³⁺-activated gallate phosphors with the spinel structure and provideda new route for design of long persistent phosphors.