Design,Preparation And Luminescence Mechanism Of Tran-Sition Metal Ions Doped Gallium Zinc Gallogermanate Near-Infrared Afterglow Nanoparticles

Recently,near-infrared（NIR）afterglow nanoparticles have attracted increasing attentions in medical imaging,disease diagnosis and therapy due to their emission wavelengths falling into the biological transparency window（650-1800 nm）.In particular,NIR afterglow nanomaterials have persistent luminescence after stopping light irradiation and can effectively avoid autofluorescence interference and photo-damage to normal tissue.At present,zinc gallogermanate based NIR-Ⅰ afterglow nanoparticles with Cr³⁺ions（d³electron configuration）as activation center have shown potential applications in biological imaging,temperature detection and photodynamic therapy.However,for NIR afterglow nanoparticles,the existed single activation center has limited the understanding of the afterglow mechanism and practical applications in deep tissue diagnosis and therapy.Especially,there remain unsolved issues on how to expand afterglow wavelengths to NIR-Ⅱ region and how to overcome a single imaging strategy to achieve more accurate and reliable diagnosis.Focusing on the above problems,a series of transition metal ions with d⁵,d⁷and d⁸electron configurations and NIR luminescence were used as activation centers and spinel-phased zinc gallogermanate(Zn₂Ga₃Ge_0.75O₈,ZGGO)with anti-defects were selected as the host.Thus,NIR ZGGO:M(M=Fe³⁺,Co²⁺,Ni²⁺)persistent luminencence nanoparticles were prepared by one-step hydrothermal synthesis combined with vacuum heat treatment technology.In this dissertation,their surface morphology,size distribution,optical properties,doping and afterglow mechanisms and potential application were systematically studied.The main results are summarized as follows:1.Fe³⁺ions（with d⁵electron configuration）doped Zn₂Ga_3-xFe_xGe_0.75O₈(ZGGO:Fe_x³⁺)NIR-Ⅰ persistent luminencence nanoparticles were synthesized.For ZGGO:Fe_x³⁺（x=0.002-0.200）nanoparticles,their average particle size is about 65 nm,and their morphology are nearly spherical.Their emission peak are located at 725 nm,which is attributed to the transition from ⁴T₁（⁴G）to ⁶A₁（⁶S）of Fe³⁺ions.Combined with ESR analyses suggest that Fe³⁺ions successfully replaced the tetrahedral and octahedral sites of Ga³⁺ions.With increasing Fe³⁺doping concentration,they prefer to occupy the octahedral sites of Ga³⁺ions.Meanwhile,it is found that the afterglow time montored at 725 nm can reach more than 15 min.In addition,ZGGO:Cr³⁺,Fe³⁺dual-function nanoprobes for autofluorescence-free afterglow and T₂-weighted MR imaging were constructed by using Fe³⁺and Cr³⁺ions co-doping strategy.Compared with the single-doped nanoparticles,the average particle size of co-doped nanparticles decreased to about 46 nm,and their particle size distribution is more uniform.The NIR afterglow emissions are about 700 nm,which are attributed to the transitions of²E→⁴A₂and ⁴T₂→⁴A₂of Cr³⁺,respectively and their afterglow decay time can exceed850 min.Excellent afterglow and MR imaging were realized by dispersing the co-doped nanoparticles into different simulated biological fluids,indicating that ZGGO:Cr³⁺,Fe³⁺nanoprobes have potential application in biological imaging and medical diagnosis and therapy.2.Co²⁺ions（with d⁷electron configuration）doped Zn_2（1-x）Co_2xGa₃Ge_0.75O₈NIR-Ⅰ afterglow nanoparticles were successfully by one-step hydrothermal synthesis and vacuum annealing.For ZGGO:Co_x²⁺（x=0.001-0.05）nanoparticles,with increasing Co²⁺ions concentration,the average particle size decreases from 65.9 to 56.1 nm,the surface morphology gradually tends to be spherical,and the agglomeration phenomenon decreases.According to the absorption spectrum and the analysis of crystal field theory,it is found that Co²⁺ions replace the tetrahedral and octahedral sites of Zn²⁺in ZGGO,respectively.From PL spectra,the emission peak with the strongest intensity is located at 685 nm,which belongs to the⁴T₁（⁴P）→⁴A₂（⁴F）transition of Co²⁺occupying tetrahedral sites,and the corresponding afterglow decay time exceeds 2 min.According to first-principles calculation,for a series of defects such as V_Zn’,V_Ga’’,V_O’,Zn’_Ga-Ga_Zn^o,the formation energy of the Zn’_Ga-Ga^o_Zndefect（about 1.88 eV）is the lowest,indicating that Zn’_Ga-Ga^o_Zndefect is easier to form in the ZGO based host.Meanwhile,in the two cases of Co²⁺ions occupying Zn²⁺ions with tetrahedral and octahedral sites(Zn_（1-1/16）Ga₂O₄:Co²⁺_1/16-Td/Oh),it is found that the difference between their formation energies is only 1.57 eV,which further provides the theorirtical evidence for confirming the spectral analysis results.Our results suggest that the study on the synthesis and optical properties of novel ZGGO:Co²⁺NIR afterglow nanoparticles is helpful for the understanding of the doping and luminescence mechanisms of zinc gallogermanate based NIR afterglow nanoparticles.3.Zn_2（1-x）Ni_2xGa₃Ge_0.75O₈（x=0-0.030）NIR-Ⅱ afterglow nanoparticles were prepared by doping Ni²⁺ion（with d⁸electron configuration）into the ZGGO host.For ZGGO:Ni_x²⁺（x=0-0.030）nanoparticles,their average particle sizes are in the range of86.2-74.2 nm,and their morphology gradually tend to be spherical.Under 590 nm excitation,their broad emission peaks can be observed in the region of 1000-1700 nm.According to Tanabe-Sugano theory,it is found that Ni²⁺ions replace tetrahedral and octahedral sites of Zn²⁺in the ZGGO host.Meanwhile,their afterglow emissions around 1290 and 1550 nm are located in the NIR-Ⅱ-A in NIR-Ⅱ-B regions,respectively,and their corresponding afterglow time exceed 30 min and 5 min.In addition,based on the energy transfer strategy between Cr³⁺and Ni²⁺ions,Zn_2（1-x）Ni_2xGa_3-yCr_yGe_0.75O₈nanoparticles were further synthesized.Compared to the single-doped nanoparticles,their NIR-Ⅱ afterglow intensity is increased by one time.In this case,Cr³⁺can be used not only as sensitizer but also as luminescence center,leading to the NIR-Ⅰ afterglow with the decay time exceeding 600 min.Our results suggest that ZGGO:Ni²⁺,Cr³⁺nanoparticles have potential applications in NIR I/Ⅱ afterglow imaging and it opens up a new way for realizing deep-tissue bioimaging.In conclusion,this study paves a way in developing novel NIR afterglow nanomaterials for precision diagnosis and therapy of cancer.