Upconversion Luminescence Of CsPbBr₃:Yb,Er/Tm/Ho Perovskite Nanocrystals

Under the excitation of 980 nm near infrared light,the upconversion luminescence nanomaterials doped with lanthanide rare earth elements emit visible light through the up-conversion process.And the light transmission window of biological tissues happens to be in this wavelength band,which enables the excitation light to penetrate biological tissues for in vivo fluorescence imaging.Based on the above advantages,rare earth doped upconversion luminescence nanomaterials have been developed rapidly.Fluorides,oxides,halides and sulphides are the main substrates of most up-conversion luminescence materials at present.In the past decades,metal halide perovskite nanomaterials have attracted a lot of research interest due to their unique photophysical properties such as long carrier diffusion length,high carrier mobility,low defect density of states,multiphoton high absorption coefficient,high photoluminescence quantum yield,long luminescence lifetime,and tunable luminescence in the entire visible broad spectrum region.The general form of metal halide perovskite is ABX₃,where A is an inorganic monovalent cation(e.g.,Cs⁺),B is an divalent metal cation(e.g.,Pb²⁺),and X is one or more halogen anions(e.g.,Cl^-,Br^-,I^-),CsPbBr₃.The special point is that CsPbX₃ perovskite nanocrystals are ionic crystals,and have the characteristics of ionic crystals.The location of the luminescence peak can be adjusted through the anion exchange reaction and the size of the crystal.However,the excellent optoelectronic properties of perovskite nanocrystals require high energy UV excitation,which is known to be harmful to the nanomaterials themselves,biological tissues and human body,leading to rapid decay of the material,significant reduction in luminescence efficiency,shortening of luminescence lifetime,and having a small penetration depth,which does not achieve the desired imaging effect.Therefore,there is an urgent need to prepare all inorganic CsPbX₃ perovskite upconversion luminescent materials,so that the perovskite materials have a large penetration depth under low energy light excitation,less damage to biological tissues,achieve better imaging effect and higher quantum yield of luminescence,and then realize the real application of perovskite materials in bioimaging,cell detection and other biomedical applications.In this paper,CsPbBr₃:Yb³⁺,Er³⁺;CsPbBr₃:Yb³⁺,Ho³⁺;CsPbBr₃:Yb³⁺,Tm³⁺were successfully synthesized by rare-earth doping perovskite material to replace Pb2+lattice position in crystal,and achieved the upconverison luminescence at 980 nm excitation.Through the regulation of reaction conditions such as reaction temperature,reaction time,injection temperature of precursor and the ratio between solvent to complexing agent,we have achieved the controlled synthesis of a variety of different morphological upconversion perovskite materials and studied their upvonverison luminescence,laying the material and photophysical foundation for the realization of multifunctional applications of perovskite materials.Perovskite materials limits its practical application is the main reason of the stability problem,because the instability of perovskite materials on the surrounding environment,mainly including water,light,heat and oxidation reduction environment,etc.,the perovskite materials can be silanized to improve the stability of the material to the surrounding environment,and the perovskite material can be changed from oil solution to water solution,so as improve the biocompatility of the material and create conditions for the practical application of perovskite materials in biomedical.