Preparation And Properties Of Bi³⁺-doped Ultraviolet Persistent Luminescence Materials

Persistent luminescent materials（PLMs）are a type of photoluminescence materials with persistent luminescence（Pers L）effect,which can absorb and store energy of the light source using their own traps under the external excitation,Pers L produced by releasing the energy of the traps after turning off the external light source.Benefited by its unique optical performance,near-infrared and visible PLMs have gained considerable attention and are widely used in various application fields,such as lighting display,optical sensing,information storage,biological imaging and therapy.In recent years,there has been an increasing demand for novel and excellent ultraviolet（UV）PLMs.However,the development of UV PLMs is lagging behand and more challenging due to the lack of suitable host or emitting centers.To further enrich the database of Bi³⁺doped UV PLMs,two novel phosphors were designed and synthesized from exploring different hosts,co-doping ions,luminescent center ion concentrations,and other different perspectives.The optical properties and application value of UV PLMs were systematically studied and analyzed.The main research contents and results are summarized as follows:（1）A series of Bi³⁺doped novel UV PLMs Mg₄Y_2-xLu_xGe₃O₁₃:Bi³⁺were successfully synthesized by high-temperature solid-state method.After excitation of a254 nm UV lamp,the materials can show ultraviolet-A（UVA）Pers L peaking at about340 nm,by adjusting the ratio of Y/Lu,the position of afterglow emission peak is continuously blue-shifted with the increase of x.To enhance the Pers L performance of the material,it was found that Li⁺co-doping significantly enhanced the Pers L intensity by co-doping different ions.The Pers L duration of Mg₄Y_1.2Lu_0.8Ge₃O₁₃:Bi³⁺,Li⁺（MYLGO）can be detected more than 100 hours.MYLGO can be rejuvenated by short-time photostimulation with a red LED or NIR laser illumination after the long-term decay.Meanwhile,the sample exhibits good stability after repeated excitation with a 254 nm UV lamp.The trap properties of the UVA Pers L of MYLGO were studied by thermoluminescence analysis.Finally,the methylene blue degradation experiment of composite MYLGO/TiO₂ further verifies that its UVA Pers L can achieve sustained photocatalysis.The material is expected to be used in fields such as sterilization and photodynamic therapy in the future.（2）A series of Bi³⁺doped novel PLMs Mg₈Lu₂Ge₆O₂₃:Bi³⁺/Yb³⁺/Ln(MLGB-Yb/Ln,Ln=Tm³⁺,Ho³⁺,and Er³⁺)were designed by high-temperature solid-state method,which exist multi-mode luminescence and dual-mode reading characteristics.Firstly,MLGB was synthesized,which can show ultraviolet-B（UVB）Pers L peaking at 306 nm and a long duration of more than 12 hours after excitation with a 254 nm UV lamp.Through the analysis of MLGB Pers L excitation spectrums and thermoluminescence curves,the trap characteristics and luminescence mechanism of UVB Pers L of materials were revealed.Subsequently,by co-doping sensitizer Yb³⁺and rare earth ion activator,MLGB-Yb/Ln emits different colors through up-conversion luminescence corresponding to rare earth ions under 980 nm excitation light.MLGB-Yb/Ln exhibits visible down-conversion luminescence,visible up-conversion luminescence（UCL）,and invisible UVB Pers L.The visible luminescence is directly detectable by human eyes;the invisible UVB Pers L cannot be perceived by human eyes,but the encrypted information can be read by a charge-coupled device camera to decode the optical information.Importantly,the unique optical properties ensure that MLGB-Yb/Ln behaves similarly to common UCL materials when observed by humans,thus enhancing the level of information encryption provided by invisible UVB Pers L.Based on the characteristics MLGB-Yb/Ln,a variety of deceptive information encryption modes were devised,indicating the application advantages of these materials in the field of information encryption.