Controllable Synthesis And Luminescent Properties Of Rare Earth Doped Na₂CaSn₂Ge₃O₁₂ And Ca₂ZnSi₂O₇ Long Persistent Luminescent Materials

Long-persistent luminescent materials have the unique property of sustainable luminescence after removing the excitation source,which has become a hot research topic in the field of biomedical applications in recent years.In particular,the application of near-infrared（NIR）long persistent luminescent materials in the field of bioimaging and the application of nano long persistent luminescent materials that can be excited by X-rays in the field of tumor diagnosis and therapy.However,the currently reported NIR long persistent luminescent materials are not abundant in type,and the short emission wavelengths lead to shallow tissue penetration depth of NIR light,which cannot achieve deep tissue imaging.In addition,the activation center of these NIR long persistent luminescent materials is mainly Cr³⁺,which has the risk of biotoxicity.Therefore,we selected Yb³⁺、Tm³⁺、Er³⁺and Ho³⁺rare earth ions,which can enhance cellular activity,and have emission energy levels in the NIR-II or III region of the penetration window of biological tissues,as dopants,and Na₂CaSn₂Ge₃O₁₂,which has long afterglow luminescence potential,as matrix materials to develop novel long persistent luminescent materials for NIR bioimaging applications.We also attempted to prepare them by one-step mesoporous silicon templating method in order to obtain nanomaterials with bio-applicability.In addition,X-ray excited long persistent luminescent nanomaterials for tumor diagnosis and therapy are facing the problems of lack of material types,a sudden decrease or even quenching of afterglow luminescence after nanosizing,inhomogeneous nanomorphology,poor monodispersity,and small specific surface area.Therefore,we choose the one-step mesoporous silicon template method,which can control the sample morphology and monodispersity well,and choose Ca₂Zn Si₂O₇,which can use mesoporous silicon as the silicon source and has the potential of long afterglow luminescence,as the matrix material,and co-doping with Mn²⁺ions and rare earth ions Yb³⁺,in order to develop a new X-ray excited long afterglow luminescence nanomaterials diagnotherapy platform.The main research conclusions are as follows:（1）The Na₂CaSn₂Ge₃O₁₂ matrix was prepared by the high-temperature solid-phase method,and the long afterglow in the near-infrared at 801 nm,970 nm,and 1553 nm was obtained by single doping of Tm³⁺,Yb³⁺,and Er³⁺,respectively,with the afterglow lasting for 10 min and covering the wavelength range from the first to the third biological transmission window（650-1600 nm）.Through the co-doping of Pr³⁺and Yb³⁺,the persistent energy transfer and mutual sensitization luminescence between Pr³⁺and Yb³⁺ion pairs were found,and the enhanced visible-NIR light（400-1200 nm）multi-band long afterglow emission was realized.The main afterglow emission peaks are the ³P₀→³H₄ transition of Pr³⁺at 486 nm,the ¹D₂→³F_3,4 transition of Pr³⁺at 608 nm and the ²F_5/2→²F_7/2 transition of Yb³⁺at 970 nm.Compared with the single doping,the co-doping of Pr³⁺and Yb³⁺not only increases the initial afterglow intensity of Pr³⁺at486 nm by 2 times,but also increases the initial afterglow intensity of Yb³⁺at 970 nm by 2.4 times and extends the afterglow duration time by 20 min.This is due to the persistent energy transfer between Pr³⁺（608 nm）and Yb³⁺（970 nm）.The energy transfer efficiency from Pr³⁺to Yb³⁺was calculated by luminescence decay curves to reach 36%.The outer quantum efficiency of Na₂CaSn₂Ge₃O₁₂:0.8%Pr³⁺,0.8%Yb³⁺emit visible light at 400-700 nm at 254 nm excitation is 1.54%.The existence of[Pr_Ca^·-V_Ca^·-Yb_Ca^·]defect cluster is inferred by analyzing the data of thermoluminescence curve and XPS energy spectrum,and it is inferred that this defect cluster is the basis of the persistent energy transfer from Pr³⁺to Yb³⁺.NIR bioimaging experiments showed that the NIR afterglow of Na₂CaSn₂Ge₃O₁₂:Pr³⁺,Yb³⁺could penetrate 25 mm thick pork tissue and be detected by a NIR camera after removing the UV excitation source,which indicated the potential for NIR bioimaging applications.However,during the preparation of Na₂CaSn₂Ge₃O₁₂:Pr³⁺,Yb³⁺nanoparticles by the mesoporous silicon template method,it was found that Ge（OH）₄ severely damaged the mesoporous spherical morphology of silica after calcination at 900℃for 3 h,resulting in serious sintering of samples,so it was difficult to synthesize Ge containing long persistent luminescent nanoparticles by the mesoporous silicon template method.（2）The Si O₂@Ca₂Zn Si₂O₇:Mn²⁺nanoparticles prepared by mesoporous silica template method have homogeneous mesoporous spherical morphology,clear pore structure and good monodispersity with an average particle size of 70 nm.The sample emits a long green afterglow in the range of 500-600 nm with a peak at 523 nm when excited by either X-rays or 254 nm UV light.Electron traps suitable for afterglow emission were introduced by co-doping Yb³⁺with energy level depths of 0.716 e V and0.762 e V,corresponding to a 9 times and 18 times increase in trap concentration and a6 times increase in afterglow time,respectively,compared with that without co-doping Yb³⁺.When further co-doping Yb³⁺,Li⁺,the green emission of Si O₂@Ca₂Zn Si₂O₇:Mn²⁺,Yb³⁺,Li⁺is enhanced by 2.3 times,but Li⁺will destroy the mesoporous spheroid morphology and make it sintered and adherent,and reduce the afterglow time of nanoparticles.Si O₂@Ca₂Zn Si₂O₇:Mn²⁺,Yb³⁺coupled with the photosensitizer Bengal Rose Red（RB）can transfer the energy of green afterglow emission to RB persistently under UV excitation.Singlet oxygen could be detected in the He La cancer cells incubated with Si O₂@Ca₂Zn Si₂O₇:Mn²⁺,Yb³⁺@RB after X-ray excitation,which confirm that Si O₂@Ca₂Zn Si₂O₇:Mn²⁺,Yb³⁺nanoparticles have great application potential in X-ray induced photodynamic therapy（X-PDT）for tumors.