Stimulus Responsive Fluorescent Encryption Materials Based On Rare Earth Europium Complexes

Counterfeit commodities on the market,including pirated software and movie,fake medicine and clothing,even counterfeit money,not only bring economic losses to owners and consumers,but also threaten the life and health of consumers.Thus,it is necessary for the government and copyright holders to increase investment in the development of anti-counterfeiting technology.In China,various anti-counterfeiting technologies are used in more than 90%of medicines,more than 15%of food,and more than 95%of tobacco and alcohol products.At present,there are more than two thousand anti-counterfeiting label companies and more than two hundred thousand employees.By 2025,the anti-counterfeiting market scale in China will reach 350billion yuan.Photoluminescence printing is one of the most widely used anti-counterfeiting methods.Almost each country uses watermark or fluorescent label on banknotes to prevent counterfeiting.However,the real information recorded by common fluorescent anti-counterfeiting materials is usually visible under the excitation of ultraviolet,visible or infrared light,which is easy to be imitated by counterfeiters.Therefore,stimulus responsive fluorescent materials will be the ideal next generation of anti-counterfeiting materials.Among the large family of stimulus responsive fluorescent materials,a kind of rare earth complexes stands out,which fluorescence can be regulated by the external environment in.It will make the goods more difficult to forge,and it will be one of the most promising candidates of high security level anti-counterfeiting materials.In this paper,based on the principle of in-situ coordination reaction,we have designed and synthesized stimulus responsive fluorescent materials,which can be used in the field of optical information storage and anti-counterfeiting.The full text is divided into the following four parts.Chapter 1:In this paper,the research background of stimulus responsive fluorescent materials is briefly described,and the main luminescence mechanisms of stimulus responsive fluorescent materials are mainly introduced.In addition,the development history of rare earth complexes is briefly introduced.The main factors that determine the fluorescence of rare earth complexes and the scheme to improve the properties of rare earth complexes are mainly introduced.Chapter 2:In this work,a smart duplicato-responsive of stimuli and time-gates nanohybrid based on variable valence Eu²⁺/Eu³⁺co-encapsulated has been fabricated and applied as active material in the multi-level and multi-dimensional memory devices.The luminescence spectra and lifetime of Eu³⁺in this nanohybrid performed a stimuli-response from the modulation of the energy level of the coordinated ligand.Furthermore,by simply sintered procedure,Eu³⁺was partially reduced to Eu²⁺with short lifetime in the system.Interestingly,Eu³⁺revealed the prolonged lifetime because of the presence of energy transfer effect of Eu²⁺?Eu³⁺.Such a nanohybrid had the abundant luminescent properties including the short lifetime of Eu²⁺,the energy transfer between the Eu²⁺and Eu³⁺,and the stimuli-response of the Eu³⁺spectra and lifetimes upon exposure to acidic or basic environments,thus giving birth to interesting recording and encryption performance in spatial-temporal dimensions.This research pointed out a new direction for the future development of multi-level and multi-dimensional optical recording and encryption materials.Chapter 3:Inorganic perovskite quantum dots(QDs)have attracted great scientific attention in the field of luminescent materials but the application has been limited by the inferior stability resulted from highly dynamic capping ligands.In this work,we use rare-earth complex to modify perovskite QDs by ligands exchange to realize perovskite functionalization,meanwhile,the stability of perovskite QDs is greatly improved.DFT calculation result shows that the adsorption energy of the europium complex to QDs is higher than traditional ligands,which provides a thermodynamic basis for stability improvement.Furthermore,the modified QDs exhibit attractive dual-response property,including temperature-and p H-response ascribed to QDs and europium complex,respectively.The superior property can be applied to multi-stimuli responsive optical encoding,which is further capable of enhancing the security of encrypted information.This study not only affords a strategy for the synthesis of highly stable perovskite,but also provides a method to the functionalization of perovskite.Chapter 4:One-dimensional(1DN)perovskite was in-situ grown in the one-dimensional channel of rare earth metal organic frame(MOF).The ordered filling structure of 1DN perovskite in the channel of MOF was determined by XRD small angle diffraction.The one-dimensional channels of MOF provide the necessary coordination environment for 1DN perovskite and greatly enhance its stability.Moreover,1DN perovskite can transfer energy to rare earth ions in MOF,which greatly enhances the fluorescence and lifetime of rare earth ions.The structure of perovskite and rare earth MOF was confirmed by synchrotron radiation.The energy transfer from perovskite to rare earth ions was observed by fluorescence spectrum.The energy band structure and luminescence mechanism of the material are discussed based on the density functional theory(DFT)results.This research not only provides a new strategy for the synthesis of low-dimensional perovskite,but also provides a way for the future development of optical information storage and anti-counterfeiting materials in time dimension.Chapter 5:Summary and outlook.