Preparation Of Cr³⁺ Doped Mg-based NIR Phosphor And Its Optical Properties Regulation

Near-infrared（NIR）luminescent materials are very important for applications in night vision,biological imaging and password security.However,thermal quenching and low chemical stability often significantly inhibit the luminous efficiency of near-infrared phosphors.In view of these problems,this thesis has carried out two works to explore the theoretical factors affecting the thermal stability of Cr³⁺doped NIR phosphors,and designed and synthesized high-efficiency phosphors.（1）The properties of near-infrared Ca（Sc,Mg）（Al,Si）O₆:Cr³⁺phosphors with pyroxene structure under blue light excitation has been studied.The end member of Ca（Sc,Mg）（Al,Si）O₆:Cr³⁺phosphor,CaScAlSiO₆:Cr³⁺,realizes broadband emission,with a half-width of215 nm.What’s more,CaMgSi₂O₆:Cr³⁺shows high thermal stability at 150℃,and its intensity can still maintain 88.4%of that at room temperature.Structural analysis and density functional theory calculation proved that the lack of soft conformation and local spatial constraints jointly lead to high structural rigidity,and achieved the purpose of weakening the thermal quenching effect.NIR pc-LED was fabricated by using Ca（Sc,Mg）（Al,Si）O₆:Cr³⁺,and the nondestructive testing of internal defects of the pestle rod was successfully realized.（2）Inspired by the first work,we consider the heterovalent substitution based on the highly rigid garnet matrix to optimize the performance of NIR phosphors.In the second work,near-infrared phosphor Y₃（Al,Mg）₂（Al,Si）₃O₁₂:Cr³⁺(YMAS:Cr³⁺)was designed by replacing the prototype Y₃Al₅O₁₂:Cr³⁺with 2[Al³⁺]→[Mg²⁺]+[Si⁴⁺].YMAS:Cr³⁺phosphor shows excellent optical properties and chemical stability,and the quantum yield（QY）reaches86–93%,the emission intensity can still maintain 94%at room temperature at 150℃,and there is almost no luminous loss after immersion in water for 8 days or heating at 1000℃.Substitution improves the local symmetry resulting in the ⁴T₂→⁴A₂transition of spin in the weak crystal field of YMAS:Cr³⁺.Compared with the ²E→⁴A₂transition of spin in the strong crystal field of prototype Y₃Al₅O₁₂:Cr³⁺（QY=16%）,it has higher efficiency and a wider emission spectrum.The potential application of YMAS:Cr³⁺near-infrared phosphor is demonstrated through the successful preparation of high-power output LED and fluorescent ink which is capable of information hiding.This study explored and summarized the theoretical factors affecting the thermal stability of the Cr³⁺doped NIR phosphors.Based on the theory,high-performance Ca Sc_1-xMg_xAl_1-xSi_1+xO₆:Cr³⁺and Y₃（Al,Mg）₂（Al,Si）₃O₁₂:Cr³⁺near-infrared phosphors have been successfully designed and synthesized.At the same time,two kinds of NIR phosphors were used to fabricate near-infrared devices with excellent performance.The research results provide theoretical reference and guidance for the designing and development of NIR luminescent materials in the future,and are expected to become a new principle for the design of NIR luminescent materials.