Synthesis And Photoluminescence Properties Of Yb³⁺ Doped Halide Perovskite

Near-infrared emitting materials have great potential applications in night vision,optical communication,biological imaging,medical diagnosis and food analysis.Therefore,highly-efficient near-infrared emitting materials has been a hot topic in the area of luminescent materials.Yb³⁺,as a species of rare-earth ions,can emit light radiation around 980 nm and achieve near-infrared emission in suitable host materials.However,due to weak absorption of the 4f-4f parity-forbidden transition of Yb³⁺,it is hard to be excited by commercial UV or blue LED chips,making it difficult to improve photoluminescence quantum yield（PLQY）of Yb³⁺-doped luminescence materials.In this paper,perovskite-structured chlorides were chosen as the matrix to investigate the synthesis methods and luminescent characteristics of Yb³⁺-doped perovskite nanocrystals/single crystals.Furthermore,a preliminary exploration of the intrinsic luminescence mechanism was conducted.The specific research content and results are presented below.Based on the traditional hot-injection method,Yb³⁺:CsPbCl₃nanocrystals were successfully synthesized using a modified hot-injection method,and optimized the process parameters such as raw material ratios,hot-injection temperature,and organic ligand addition during the synthesis.Due to the difference in atomic radius and valence state between Yb³⁺and Pb²⁺,appropriate raw material ratios and temperatures play an important role in promoting Yb³⁺to occupy Pb²⁺lattice and enhancing Yb³⁺emission.At the same time,effective ligand protection is also the key to ensure the luminescence performance of quantum dots.The synthesized Yb³⁺:CsPbCl₃achieved intensive near-infrared emission around 985 nm under 365 nm excitation.Yb³⁺:Cs₂AgBiCl₆nanocrystals and single crystals were synthesized by hot-injection and hydrothermal methods,respectively.Yb³⁺ions could be successfully introduced into the Cs₂AgBiCl₆host and the photoluminescence properties were studied.Under excitation by 365 nm ultraviolet light,both Yb³⁺:Cs₂AgBiCl₆nanocrystals and single crystals exhibit characteristic luminescence near 985 nm from Yb³⁺ions.Compared to Yb³⁺:Cs₂AgBiCl₆nanocrystals,Yb³⁺:Cs₂AgBiCl₆single crystals are more conducive to achieving effective Yb³⁺ion doping.The energy transfer between self-trapped excitons（STE）in the Cs₂AgBiCl₆matrix and Yb³⁺ions enables stronger Yb³⁺near-infrared luminescence.Furthermore,Yb³⁺:Cs₂AgBiCl₆single crystals were far superior to Yb³⁺:Cs₂AgBiCl₆nanocrystals in terms of chemical stability.（1）Based on Yb³⁺:Cs₂AgBiCl₆,the effects of B⁺and B³⁺element substitutions in the double perovskite structure on its luminescent properties was investigated.In Yb³⁺:Cs₂AgBiCl₆nanocrystals and single crystals,Na⁺substitution for Ag⁺or Al³⁺substitution for Bi³⁺could significantly enhance the STE emission of Cs₂AgBiCl₆.Similarly,the near-infrared emission intensities of Yb³⁺in Cs₂（Ag/Na）Bi Cl₆and Cs₂Ag（Bi/Al）Cl₆hosts were higher than that in Cs₂AgBiCl₆.The incorporation of Na⁺and Al³⁺broke the symmetry of the[Ag Cl₆]^5-octahedrons,promoting the formation of STE,and further enhance Yb³⁺ion emission.Specifically,through energy transfer from STE to Yb³⁺,the emission from Yb³⁺ions is further enhanced.Compared to Yb³⁺:Cs₂AgBiCl₆,Yb³⁺:Cs₂Ag_0.2Na_0.8Bi Cl₆exhibits a twofold increase in near-infrared emission intensity near 985 nm.