Structural Design And Multi-functional Application Of Lead-free Zero-dimensional Metal Halide Luminescent Materials

Lead-free zero-dimensional（0D）metal halide luminescent materials have become a cutting-edge research hotspot in the field of optical functional materials and devices due to their unique composition,structure,and luminescence characteristics.The advantages of low-cost solution synthesis,non-toxic,excellent photoluminescence/radioluminescence properties make them hopeful to replace the traditional all inorganic scintillator crystals and photoluminescence materials in some application scenarios.Based on this,this research paper focuses on the basic and multifunctional application research of lead-free 0D metal halides.Guided by X-ray detection and lighting applications,we design and synthesize several new lead-free 0D metal halide luminescent materials to address the scientific issues faced by 0D metal halide materials in the fields of X-ray detection,white LED lighting,and near-infrared night vision lighting.Further,we depthly analysize the relationship between the crystal structure and luminescence properties of these materials,providing a new idea and method for designing new optical functional materials.The main research contents are as follows:（1）Novel 0D Cu⁺-based hybrid metal halide scintillator(C₈H₂₀N)₂Cu₂Br₄ with excellent radioluminescence property has been designed.Upon 320 nm excitation,it exhibits strong blue emission peaking at 468 nm with a near-unity photoluminescence quantum yield（PLQY）of99.7%.Taking commercial Lu AG:Ce as the standard,the calculated light yield of(C₈H₂₀N)₂Cu₂Br₄even up to～91300 photos/Me V,which is the reported highest value for Cu⁺-based metal halide scintillators.The lowest detection limit is confirmed to be as low as about52.1 n Gy_air s^-1 when the signal-to-noise ratio is 3,which is more than one hundred times lower than the dose rate of 5.5μGy_air s^-1 for labeled X-ray medical diagnostics.Moreover,(C₈H₂₀N)₂Cu₂Br₄ crystals display remarkable stability under various conditions,such as continuous X-ray irradiation,high-energy UV illumination,and storage under ambient conditions.The(C₈H₂₀N)₂Cu₂Br₄ ceramic wafer based on the cold pressing sintering process（CPSP）was fabricated and a spatial resolution of 9.54 lp/mm is derived in nondestructive X-ray imaging.（2）Novel 0D Cu⁺-based hybrid metal halide（1,3-tpp H₂）₂Cu₄I₈·H₂O with excellent water stability and blue-light-excitable characteristic has been designed.Density function theory（DFT）calculation demonstrates that organic cation contributes to the conduction band minimum（CBM）,which makes this compound exhibit a small optical band gap,thereby enables it show blue-light-excitable characteristic.Under 460 nm excitation,it shows the bright broadband orange-red emission peaking at 625 nm.Moreover,theπ-πinteraction generated by the layered stacking of organic cations makes（1,3-tpp H₂）₂Cu₄I₈·H₂O show the excellent water stability,and photoluminescence（PL）properties show negligible changes even after continuous water treatment for 60 days.The fabricated LED device by combining the commercial LED chip（In Ga N,～440 nm）,green Lu₃Al₅O₁₂:Ce（Lu AG:Ce）and（1,3-dpp H₂）₂Cu₄I₈·H₂O shows the warm white-light emission with the Commission Internationale de I’Eclairage（CIE）color coordinate of（0.445,0.399）,correlated color temperature（CCT）of 2823 K,and color rendering index（R_a）of 91.4%.（3）Novel 0D metal halide near-infrared luminescent material Cs₂Zn Cl₄:Sb³⁺has been designed using ion doping strategy.Upon 316 nm excitation,Cs₂Zn Cl₄:Sb³⁺crystals show a broadband near-infrared（NIR）emission peaking at 745 nm with the highest PLQY of up to69.9%.The steady/transient-state spectra show that the broadband NIR emission with large Stokes shift comes from the triplet self-trapping excitons（STEs）emission of Sb³⁺ions.In addition,Cs₂Zn Cl₄:Sb³⁺crystals have excellent air and thermal stability.The structure and PL spectra of Cs₂Zn Cl₄:Sb³⁺crystals almost maintain unchanged after being stored in the ambient atmosphere for 6 months.Moreover,Cs₂Zn Cl₄:Sb³⁺crystals present a relatively low luminescence thermal quenching behavior and the integrated PL intensity still maintains 73%of the initial intensity measured at 150°C,which is also much higher than that of recently reported metal halide luminescent materials.A NIR LED device suitable for near-infrared imaging is prepared by combining a 365 nm LED chip and Cs₂Zn Cl₄:0.2Sb³⁺material.（4）Based on theoretical analysis of polyhedral configurations of metal halides,three novel0D hybrid antimony halides(C₁₃H₂₂N)₂Sb₂Cl₈（1）,(C₁₀H₁₆N)₂Sb₂Cl₈（2）,and(C₁₆H₃₆P)Sb Cl₄with dimeric configurations were designed,achieving ultra-large Stokes shifted broadband NIR emissions.Under 350,345,and 335 nm excitation,compounds 1,2,and 3 show the unusual broadband NIR emissions peaking at 865,990 and 1070 nm,respectively.By combining the exciton self-trapping model and the PL properties,we attribute the particular broadband NIR emission of these compounds to triplet（³P₁→¹S₀）STEs emissions confined in[Sb₂Cl₈]^2-dimer.Excited-state structure calculation further demonstrates that[Sb₂Cl₈]^2-dimer has lower structural symmetry with greater structural freedom,under light excitation,the large excited state structural distortion of[Sb₂Cl₈]^2-dimer enables them to show the abnormal broadband NIR emissions.