Design Of Lanthanide Doped Multi-mode Luminescent Materials For Anti-counterfeiting Application

Counterfeiting has brought huge economic loss and serious security risk,hence efficient ant-counterfeiting techniques are urgently needed to solve this problem.Luminescent anti-counterfeiting materials have attracted great interests owing to their good concealment,abundant emission color and apparent anti-counterfeiting phenomenon.However,traditional single-mode luminescent anti-counterfeiting materials only emit one color of light under the excitation of single mode,which is easy to be duplicated.The design and development of multi-mode luminescent anti-counterfeiting materials which have different emission colors under different excitation sources is an important method to solve this problem.Among them,lanthanide doped luminescent materials have advantages of good stability,ultraviolet and infrared lights excitation,high color purity,visible light emissions and so on.Hence they are ideal candidates for efficient multi-mode luminescent anti-counterfeiting which have broad prospects in anti-counterfeiting application.In this paper,three multi-mode luminescent anti-counterfeiting materials were designed to offer new ideas for anti-counterfeiting.The crystal structures,photoluminescence properties,emission mechanisms and anti-counterfeiting application were explored in details,and main work of this thesis are shown in the following three parts:(1)GdF₃:Yb³⁺,Tm³⁺,Eu³⁺dual-mode luminescent anti-counterfeiting materials were synthesized via hydrothermal method,and the dual-mode luminescent anti-counterfeiting was achieved by the orange light and violet light of samples under excitation of 365 nm and 980 nm.The energy transfer process between ions was investigated by PL spectra and decay curve,and the possible up/down conversion processes were given.The anti-counterfeiting pattern was printed by screen printing technique to realize dual-mode luminescent anti-counterfeiting.(2)In order to improve the anti-counterfeiting properties,Sr Bi₄Ti₄O₁₅:Er³⁺dual-mode luminescent anti-counterfeiting materials were synthesized by high temperature solid state method.Dual-mode luminescent anti-counterfeiting was achieved by the green and red emissions under 980 nm and 1550 nm lasers respectively,and different up-conversion multi-photon processes of Er³⁺under two excitation wavelengths were explored.Meanwhile,the concealing of important information was realized using orange emission color of Sr Bi₄Ti₄O₁₅:0.5%Er³⁺and red emission color of Sr Bi₄Ti₄O₁₅:3.0% Er³⁺under1550 nm laser.and the emission mechanisms were analyzed in details.The possible luminescence process was given to provide an idea for three mode luminescent anti-counterfeiting using 1550 nm laser as excitation source.(3)Ba₂GdTaO₆:Mn⁴⁺,Er³⁺three modes luminescent anti-counterfeiting materials were synthesized by high temperature solid state method.Three modes luminescent anti-counterfeiting was achieved by the deep red,yellow-green and yellow emissions under the excitation of 365 nm,980 nm and 1550 nm sources.The emission color change and the energy transfer processed related to Er³⁺and Mn⁴⁺dopant concentrations under the excitation of infrared and ultraviolet light sources were investigated by PL,PLE Spectra and decay curve,and the possible up/down conversion luminescence processes were given.Anti-counterfeiting patterns were printed by screen printing technique to realize three modes luminescent anti-counterfeiting.It provides a new idea for the design of multi-mode luminescent anti-counterfeiting materials.