Luminescent Properties And Applications For Anticounterfeiting In A Lithium Niobate Doped With Rare Earth

Lithium niobate is a human-made dielectric material.Its crystal structure belongs to the trigonal system and the space group is R-3c.Because of excellent performance,such as low phonon energy,non-toxicity,high physical and chemical stability,simple preparation methods,etc.,Lithium niobate mostly used as a host material for rare earth luminescence.In this work,LiNbO₃:RE³⁺(RE³⁺=Pr³⁺,Er³⁺,Tm³⁺,Yb³⁺)with high crystallinity was successfully prepared by the solid-state reaction.It should be noted that six types of luminescence for LiNbO₃:RE³⁺have be obtained in the same host material by doping different rare earth ions,including downconversion luminescence,persistent luminescence,photostimulated luminescence,thermoluminescence,upconversion luminescence and mechanoluminescence respectively.In addition,we systematically studied their luminescent properties.By combining different types of luminescent modes,four anticounterfeiting devices were developed successfully.First,we achieved a simple downconversion luminescent mode by doped the Pr³⁺,Er³⁺and Tm³⁺ions into the LiNbO₃ matrix.And a multi-color down-conversion luminescence material was achieved by changing the doping ratio of the three ions.Secondly,by doping Pr³⁺into the LiNbO₃ matrix and adjusting depth of trap levels,we were obtained two different trap depth materials(Li_0.99NbO₃:1mol%Pr³⁺and LiNbO₃:1mol%Pr³⁺).Interestingly,different trap depth materials have different luminescent mode.Among them,Li_0.99NbO₃:1mol%Pr³⁺has shallow trap depth,and it has a persistent luminescence mode,while LiNbO₃:1mol%Pr³⁺has deep,which can realize luminescent modes such as mechanoluminescence,photostimulated luminescence and thermoluminescence.Finally,Er³⁺and Tm³⁺/Yb³⁺ions were doped into lithium niobate to achieve the up-conversion luminescence mode.In order to obtain the multi-color upconversion luminescence effect,we made a systematic study of LiNbO₃:Er³⁺materials.It is worth mentioning that we tuned the color of the up-conversion luminescent material by adjusting reaction temperature,laser power,and doping concentration,and analyzed the cause of the discoloration.By combining the upconversion luminescence and photostimulated luminescence mode,the dynamic color change is achieved.In order to apply the prepared luminescence materials,we used different luminescent modes and combined the luminescent materials with PDMS or epoxy resin to obtain luminescent anticounterfeiting devices with different modes.Firstly,the multicolored"rainbow landscape"anticounterfeiting device based on downconversion luminescence was fabricated.Secondly,a flexible dual-mode anticounterfeiting device with the words"Lanzhou University"based on the persistent luminescence and the mechanoluminescence was achieved by combing the materials was combined with PDMS.Besides,and a dual-mode of double-layer dynamic anticounterfeiting device based on upconversion luminescence and photostimulated luminescence was obtained.Finally,based on the modes of downconversion luminescence,thermoluminescence,upconversion luminescence and photostimulated luminescence,a luminescent trademark of the Lanzhou hand-pulled noodles is designed for four-mode anticounterfeiting and the mark of freshness by combining the materials with PDMS.