Research On Properties Of Rare Earth Luminescence Materials For Anti-counterfeiting And Encryption

Anti-counterfeiting and encryption technology have been playing important roles in the progress of human civilization.And among them,the luminescent materials have been generally regarded as the most ideal anti-counterfeiting and encryption technology owing to their advantages of visibility,facile design and the convenient operation.However,the conventional luminescent materials used in security designs mainly exhibit a single-or dual-mode fluorescence under excitation with ultraviolet(UV)or near-infrared(NIR)light,which can be easily counterfeited by utilizing certain substitutes with similar emission in some cases.Thus,it is urgent to design and develop novel multimodal luminescent materials.Inorganic luminescent materials doped with rare earth ions(Ln³⁺),as a kind of the senior phosphor family,have attracted much attention due to their excellent luminescence properties.The remarkable advantages of the Ln ions and inorganic matrix materials offer great possibilities for the creation of the multimodal luminescence.For example,Ln ions are efficient luminescent centers with a library of absorption and emission energy levels,covering a wide spectral range between UV-vis and NIR.The combination of Ln ions with different emission colors can produce the required multi-color emission.Also,inorganic hosts generally have stable physical and chemical properties,low toxicity and excellent environmental tolerance,which make them of great application value in daily life.More importantly,in addition to containing the Ln ions,the inorganic matrix lattice also has an interaction with the Ln ions via the crystal field,energy migration and charge compensation effects to produce complex emission patterns,such as photo-luminescence,thermo-luminescence,up-conversion luminescence,persistent luminescence,mechanoluminescence and photo-stimulated luminescence.So in this work,we doped different rare earth ions into inorganic host to realize multimodal luminescence for the application of anti-counterfeiting and information encryption.The specific researches are as follows:(1)We have designed and synthesized a new luminescent material Zn₄B₆O₁₃:Tb³⁺,Yb³⁺with persistent luminescence,photo-luminescence,up-conversion luminescence and thermo-luminescence simultaneously.Tb³⁺ions were chosen as the emitting centers for multimodal emissions and Yb³⁺co-doping can be used as electron traps and sensitizer to achieve the tailoring of trap distribution and efficient up-conversion luminescence in rare earth doped luminescent materials.Besides,the as-prepared luminescent materials exhibit high thermal stability and excellent water resistance.Based on these properties,the samples were used to print luminescent images through a screen printing process on the film and banknote for the application of anti-counterfeiting and information encryption.(2)We have discovered and synthesized a rare earth single-doped material Mg₂Sn O₄:Tb³⁺with persistent luminescence,photo-luminescence and photo-stimulated luminescence.Firstly,Mg₂Sn O₄was selected as the host because of its inverse spinel crystal structure and a large number of intrinsic traps,which has blue photo-luminescence and persistent luminescence.After introducing the Tb³⁺to regulate the traps and generate photo-stimulated luminescence,we found a distinction of emission color between photo-luminescence,persistent luminescence and photo-stimulated luminescence.Thus,a multimodal dichromatic luminescence was achieved by single doping.Based on the luminescence properties,we made the obtained samples into chalks and directly write some hidden information on the substrates for the application research of high-level information encryption and anti-counterfeiting.