Light-Emitting Properties Of Spectrally Tuned Lead-Free Double Perovskite Cs₂AgInCl₆

The toxicity of lead in lead-based halide perovskites and its instability are the main reasons limiting its commercial application.People around the world are looking for materials with high stability and low toxicity as alternatives to lead-based halide perovskites.The excellent stability and low toxicity of the lead-free double perovskites Cs₂AgInCl₆ and its direct bandgap characteristics make it suitable as a luminescent material.However,Cs₂AgInCl₆ still has some shortcomings in optical performance:its luminescence efficiency is low because of the problem of odd-even forbidden leap;the excitation light source requires a high energy UV light source,which is difficult to be excited by blue light;the wide half-height width of the emission spectrum cannot be applied to the display field;the stability is not enough to support commercial applications.In this paper,we discussed the enhancement of PL intensity and blue light excitation by Yb³⁺doping of Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆,prepared Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆@KSCN to achieve blue light excitation and narrowed spectrum and the preparation of Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆@CTAB nanocrystals（NCs）by anti-solvent method to improve the luminescence intensity and humidity stability.Details are as follows:We synthesized Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Yb_xCl₆ material that can be excited by blue light.The blue excitation can be achieved at room temperature by adding Yb³⁺ions to Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆.When Yb³⁺is introduced,the self-trapped exciton luminescence center is not changed.By adding Yb³⁺ions,a trap energy level E_i has been generated.The trap energy level E_i is affected by thermal expansion,and excitons can leap directly from E_i to STEs at room temperature to achieve blue excitation.It is expected that in the future,the blue light excitation performance of lead-free double perovskite Cs₂AgInCl₆ at room temperature can be further improved and higher luminescence efficiency can be achieved for better applications in optoelectronic devices,display luminescence and solar cells.The new material Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆@KSCN was synthesized by solid phase method.After introducing KSCN into the Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆ system and at temperatures below 160 K,the samples can achieve blue excitation and narrow spectrum emission of FWHM only 38 nm.The narrowing of the emission peak was only achieved at room temperature.The analysis of the absorption spectra and PLE spectra revealed a new strong absorption peak near 500 nm after the addition of KSCN,and the PLE spectra were able to correspond to it at low temperatures of 10-160 K,which supported the blue excitation of the material.The results of the temperature-dependent PL and TRPL fits analyze the luminescence mechanism of the material and demonstrate that a very narrow emission spectrum with blue excitation can be achieved in the temperature range of 10-160 K.A novel nanomaterial Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆@CTAB NCs was prepared using the inverse solvent method.The introduction of CTAB into the Cs₂Ag_0.6Na_0.4In_0.8Bi_0.2Cl₆ system improves the PL intensity of perovskite by passivating the NCs surface defect state and forming a Br-rich surface.The long carbon chain structure of CTAB is utilized and attached to the surface of perovskite to improve the moisture stability of the material through its van der Waals and hydrophobic forces.Photoluminescence（PL）spectra and absorption spectra revealed that the introduction of CTAB could well improve the PL intensity of the material.The good humidity stability of the material was demonstrated by moisture tolerance test,which provides the possibility of future optoelectronic devices for underwater lighting or wet environment applications.