Preparation And Nonlinear Optical Properties Of All Inorganic Lead-free Perovskite Quantum Dots

Both organic perovskite quantum dots CH₃NH₃Pb X₃（X=Cl,Br,I）and inorganic perovskite quantum dots Cs Pb X₃（X=Cl,Br,I）based on excellent linear and nonlinear optical effects are widely employed in the fields of military affairs,optical engineering and other aspects recently.However,larger optical limiting（OL）threshold,toxicity of Pb and instability limit wider applications.Herein,Cs₃Sb₂X₉ QDs,Cs₃Bi₂X₉ QDs and Cs₃Cu₂X₅ QDs,are prepared by supersaturated crystallization.Transmission electron microscope（TEM）,scanning electron microscope（SEM）,energy dispersive spectroscopy（EDS）,X-ray powder diffractometer（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman,UV-visible spectrophotometer（UV-Vis）,fluorescence spectroscopy（PL）are used to study the synthesis technology,parameters and components on the microstructure and luminescence properties of materials.The nonlinear absorption（NLA）and OL characteristics are studied by using the open-hole Z-scan technique under the irradiation of 532 nm laser.Finally,the potential advantages of all inorganic lead-free perovskite quantum dots in the practical application of optical limiter materials are discussed.The main contents as follows:（1）Cs₃Sb₂X₉ QDs are prepared by supersaturated recrystallization method.The results show that the Cs₃Sb₂Br₉ QDs crystallize well with an average size of 4.815 nm.Due to the interaction between medium and solvent,the fluorescence emission is wavelength dependent.Cs₃Sb₂Br₉ QDs have strong free carrier absorption nonlinear absorption properties due to two-photon excitation,and OL threshold is derived as F_th=2 J/cm² at the laser energy of 60μJ.（2）Cs₃Bi₂X₉ QDs are prepared by supersaturated recrystallization method.The results show that Cs₃Bi₂Br₉ QDs are spherically dispersed with an average size of 3.979nm.They are excitation wavelength dependent,and the emission wavelength can produce a tunable wavelength range of 70 nm.The OL threshold is derived as F_th=1.86J/cm²at the laser energy of 60μJ.（3）Cs₃Cu₂X₅ QDs are prepared by supersaturated recrystallization method.The results show that the Cs₃Cu₂Br₅ QDs is spherical with an average size of 4.815 nm.The excitation wavelength is obviously dependent.By changing the excitation wavelength,a tunable wavelength range of 90 nm can be generated.Cs₃Cu₂X₅ QDs exhibits the reverse saturation absorption characteristic,and the optical limiting characteristic of Cs₃Cu₂Cl₅ QDs is better than that of other halogens.The OL threshold is derived as F_th=1.1 J/cm² at the laser energy of 60μJ.All inorganic lead-free perovskite quantum dots are non-toxic and stable,and have better optical limiting threshold than lead-based perovskite quantum dots,which are potential nonlinear optical materials.