Preparation And Luminescence Properties Of Novel Cr³⁺-activated Garnet Structured Near-infrared Phosphors

Broadband near-infrared light has broad application prospects in biomedicine,pesticide residues,artificial intelligence,drone imaging,and security monitoring.Compared with traditional near-infrared light sources,near-infrared phosphor-converted LED devices（NIR pc-LED）have many advantages such as adjustable emission peak,low cost,long life,energy saving,environmental protection and high luminous efficiency,and have become a research hotspot in recent years.Among them,the garnet-structured matrix has the advantages of tunability,good thermal stability,and abundant polyhedral sites,which can provide a good crystal field environment for Cr³⁺ions,thereby realizing efficient and broadband near-infrared luminescence.However,most of the reported Cr³⁺-activated garnet-structured near-infrared phosphors with high optical efficiency and good thermal stability are expensive Sc-based phosphors,which hinders their practical application.Based on this,this thesis utilizes the tunability of the garnet structure to develop a new and inexpensive Cr³⁺doped garnet structure broadband near-infrared phosphor by changing the composition of the matrix structure.The main findings are as follows:（1）Lu₂Ca Mg₂Si₃O₁₂:Cr³⁺garnet structure near-infrared phosphors were synthesized by high temperature solid-phase method.Under the excitation of 450 nm,Lu₂Ca Mg₂Si₃O₁₂:Cr³⁺exhibits a broadband emission from 650 to 1100 nm,the emission peak is located at 752 nm,and full width at half maximum is 125 nm.Under the optimal Cr³⁺doping concentration（5 mol%）,the internal quantum yield（IQE）of the phosphor is76%,and its luminescence intensity at 423 K is 70%of that at room temperature.The emission peak of the Lu₂Ca Mg₂Si₃O₁₂:Cr³⁺phosphor has a good coincidence with the phytochrome absorption peak(P_FR)of the plant,indicating that the near-infrared light generated by the phosphor can be used as a fill light for plants,and has great potential in the agricultural field.application prospects.（2）Na₃X₂Li₃F₁₂:Cr³⁺（X=Al,Ga,In）garnet structure fluoride near-infrared phosphors were synthesized by hydrothermal synthesis.The synthesized Na₃X₂Li₃F₁₂:Cr³⁺（X=Al,Ga,In）phosphors have regular morphology and good dispersion.Under the excitation of blue light,the three phosphors exhibited broadband emission centered at 752,764,and 778 nm with full width at half maximum of 101,117,and 121 nm,respectively.The IQE and external quantum efficiency（EQE）were 41.9%and 48.7%,respectively.,87.2%and 3.12%,7.79%,20.05%.Among the three phosphors,Na₃Al₂Li₃F₁₂:Cr³⁺has the highest thermal stability（83%of room temperature emission intensity at 423 K）,Na₃In₂Li₃F₁₂:Cr³⁺phosphor has the highest emission intensity and the strongest electron-phonon interaction.Under the current of 350 m A,the NIR pc-LED devices packaged by the three phosphors have near-infrared output power and photoelectric conversion efficiency of 36.8 m W,107.32 m W,149 m W and 3.5%,10.1%,and 14.3%,respectively.The high-power NIR pc-LED devices packaged by Na₃In₂Li₃F₁₂:Cr³⁺phosphors have high penetrability to biological tissues,indicating that this series of phosphors have great application potential in the field of biomedicine.