Preparation And Properties Of Lead-free Halide Perovskite Luminescent Materials

The crystal structure of lead halide perovskite materials with the general formula APb X₃,where A is CH₃NH₃⁺（MA）,CH（NH₂）₂⁺（FA）or Cs⁺,and X is Cl,Br or I,have been extensively studied since the mid-20th century.They are widely used in solar cells,light-emitting diodes（LED）,because of their strong light absorption,low exciton binding energy and long carrier diffusion.The power conversion efficiency（PCE）of photovoltaic devices using lead halide perovskite has rapidly increased from 3.8%to 25.2%in only 9 years.Lead perovskite halide nanomaterials have the advantages of high photoluminescence quantum yields（PLQY）,good optical stability,full width at half maximum（FWHM）and high color purity.However,Pb is a heavy metal hazardous to human health,and its toxicity hinders its further application.In order to avoid the problem of its toxicity to the environment,researchers have tried to replace Pb with various other non-toxic elements.So far,many significant advances have been made in the preparation of lead-free chalcogenides using non-toxic elements instead of elemental Pb.In this paper,we mainly synthesize ion-doped lead-free chalcogenide luminescent materials under hydrothermal conditions,and systematically study and discuss their crystal structure,optical properties,stability,and applications of optical properties.Finally,some suggestions for the future research and development process of lead-free inorganic chalcogenide materials are discussed.The details are summarized as follows:1.Photoluminescence properties of environmentally friendly vacancy-ordered tin-based metal halide perovskiteCs₂Sn Cl₆microcrystals with pure phase and uniform size were prepared by hydrothermal synthesis.Then,Bi ions were doped into Cs₂Sn Cl₆microcrystals and their luminescence properties were tested.Under the excitation of 365 nm light,Cs₂Sn Cl₆shows blue emission with a peak position at 455 nm and a FWHM of 66nm,this emission was not observed in undoped Cs₂Sn Cl₆.With the increase of Bi doping concentration,the luminescence intensity of Cs₂Sn Cl₆:x%Bi in the visible region gradually increases.When the Bi doping amount is 25%,it reaches the maximum and begins to decrease.When Bi _Sn+V_Clis formed,the undoped Cs₂Sn Cl₆has no such characteristic emission phenomenon.It is worth mentioning that the system also has a luminescence phenomenon in the NIR region.Under the excitation of 378 nm,Cs₂Sn Cl₆:x%Bi has an emission peak at 1112 nm,which may originates from the ³P₁→³P₀transition of Bi⁺,and the FWHM is 57 nm.Based on the excellent stability of Cs₂Sn Cl₆:x%Bi microcrystalline,the corresponding LED light-emitting device was fabricated.By coating Cs₂Sn Cl₆:x%Bi microcrystals on LED chip,LED device with color coordinates of（0.318,0.374）were obtained,which provides the possibility for LED applications of tin-based halide perovskite luminescent materials.2.Ce³⁺ion doping achieves broadband luminescence of Cs₂Zr Cl₆perovskiteCe³⁺doped Cs₂Zr Cl₆perovskite materials were prepared by hydrothermal method.When the matrix is not doped,the corresponding spectroscopic characterization shows that under the excitation of 270 nm light,Cs₂Zr Cl₆exhibits a broad-band blue emission centered at 450 nm,with a FWHM of 66 nm.When the optimal doping ratio of Ce³⁺is 30%,under 270 nm excitation,the characteristic peak of Ce³⁺ion appears at 360 nm.Ce³⁺ion doped Cs₂Zr Cl₆perovskite luminescent material is expected to become a new blue light material.The temperature-dependent spectral data show that the ratio of the integrated intensity of Ce³⁺ion emission to self-trapped exciton emission changes significantly with temperature,which proves that the material has certain fluorescence temperature sensing potential.The material exhibits a two-color luminescence conversion phenomenon under different excitations of 254 nm and 302 nm,showing a certain anti-counterfeiting effect.