Design,Synthesis And Properties Of Near Infrared Mechanoluminescence Materials

Mechanoluminescence(ML)material is a medium that converts mechanical energy to photon emissions under external mechanical stimuli such as tension,compression,shear force and friction,and it finds potential application prospects in many fields such as artificial intelligence skin,structural health diagnosis and stress sensors.This thesis conducted research work based on the design and preparation of new ML materials,aiming at the current in-situ,real-time detection of stress distribution in organisms for the needs of luminescent spectral bands,luminescence intensity and application methods of ML materials,through material design,mechanism research and performance testing,etc.and systematically carried out the design,synthesis and performance research of high-performance near-infrared(NIR)ML luminescent materials.The main results achieved are as follows:1 Breaking through the traditional single rare earth ion doping strategy to design ML materials,three new types of NIR ML materials activated by rare earth ions(Nd³⁺and Pr³⁺),transition metal ions(Cr³⁺)and intrinsic defects have been constructed.(1)Rare earth ion doping:(1)In the afterglow system Sr₃Sn₂O₇:Nd³⁺,the NIR ML of both the host Sr₃Sn₂O₇ and Nd³⁺ions have been reported,with corresponding ML peaks at?800 and?900 nm,respectively;(2)NIR ML was obtained from Nd³⁺activated piezoelectric material Li Nb O₃.The luminescence is located at 850-1000 nm,and the strongest peak is 895 nm;(3)Visible to NIR ML(400-1000 nm)was reported from Li Ga₅O₈:Pr³⁺.(2)Transition metal ion doping:The ML of the transition metal ion(Cr³⁺)has been discovered in addition to Cu and Mn,and its ML in Li Ga₅O₈:Cr³⁺is located in the NIR spectral band,including the ²E?⁴A₂ narrow-line forbidden transition at 716 nm and ⁴T₂?⁴A₂broadband parity allowed transition at 730-830 nm.(3)Intrinsic defects:A non-doped NIR ML material Na₂CaSn₂Ge₃O₁₂ was found,whose luminescence spans from 600 to 1000 nm with the strongest emission peak at 780 nm,and the source is relatedd to the[Sn O₆]octahedron.2 Exploring the relationship between ML intensity and defects,and proposing three methods for NIR ML intensity and test optimization:(1)Increasing the concentration of deep defects.In the LiGa₅O₈:Cr³⁺system,it is found that the NIR ML intensity of Cr³⁺is related to the proportion of deep defect P₃(1.06 e V).The higher the proportion of P₃,the stronger the ML intensity.The co-doping of Al³⁺ions can increase the proportion of deep defects,and finally the optimal NIR ML intensity was obtained when the co-doped Al³⁺ion concentration is 0.04 mol%.(2)Controlling the test time.Adjusting the test time window based on the lifetime of the ML material can optimize and improve the signal-to-noise ratio of luminescence detection.The NIR ML of the host in Sr₃Sn₂O₇:Nd³⁺can only be measured within 1 min after the pre-irradiation,within this time window,the ML of both the host and Nd³⁺ions can be obtained.If the test time is extended,only NIR ML signals from Nd³⁺ions can be obtained.Meanwhile,in the Li Nb O₃:Nd³⁺system,the NIR ML intensity gradually weakened with the extension of the test time(1?5 min),and the ML intensity measured in the first 1 min was stronger.This method of enhancing NIR ML intensities is also effective in defect-controlled NIR ML materials.(3)Doping NIR ions which are more"sensitive"to stress.For example,even when Sr₃Sn₂O₇and Li Nb O₃ are doped with NIR emission ions such as Er³⁺,Ho³⁺,Nd³⁺or Tm³⁺,only Nd³⁺ions emit NIR photons.Besides,the NIR ML intensity(800 nm)of the Sr₃Sn₂O₇ is greatly enhanced,and the reason may be that the Nd³⁺ions"bridges"the mechanical stimulation to the host lattice.3 Combining the characteristics of NIR and ML emissions,the potential applications of such materials were explored.(1)The application of NIR ML materials in biological stress imaging has been demonstrated.Under the same experimental conditions,ML from the three materials Sr₃Sn₂O₇:Nd³⁺,Li Nb O₃:Nd³⁺and Li Ga₅O₈:Cr³⁺can penetrate biological soft tissues(pig skin,fat and lean meat),and among them,Sr₃Sn₂O₇:Nd³⁺can even penetrate hydroxyapatite(the main component of human bone).It is expected that those materials can be used as a stress sensing material to achieve in-situ and real-time biological stress imaging in vitro observation.(2)The application of NIR ML materials in anti-counterfeiting signatures has been provided.In the signing process,by changing the signature speed and strength,different ML intensities can be obtained on the film.Recording these signals can reflect the signature of the signer's personal signature and can be used for anti-counterfeiting identification;secondly,the light optical signal is NIR light and it is difficult to directly observe by naked eyes and then imitate,thereby improving the anti-counterfeiting level.