Publication date: 13th July 2024
In recent years, inorganic perovskites, particularly lead-halide perovskites, have garnered significant interest due to their electro-optic properties. However, due to lead toxicity, there is a growing focus on lead-free double perovskites. In these materials, Pb+2 is substituted with In+3 and Na+/K+ cations to maintain charge neutrality. In double perovskites, the dominant emission is attributed to localized self-trapped excitons, which are less sensitive to confinement effects and are commonly utilized in nanocrystal engineering.
However, self-trapped excitons are strongly influenced by internal lattice straining. We selected a system with a substantial difference in the ionic radius of substitutional cations, aiming to maximize intrinsic strains. By varying Na-K alloy ratios within Cs2Na1-xKxInCl6, we study the resulting structures and electro-optic properties.
In this study for the first time the alloyed compositions of Cs2Na1-xKxInCl6 (Sb-doped) nanoparticles are explored. Our all-liquid synthesis yields highly crystalline, moderately emissive 36% PLQY nano-cubes, approximately 12 nm in size. Variations in the Na to K (B' site) cation ratios resulted in tunable photoluminescence emission and a significant Stokes shift. The substitution of Na with K ions shifted the emission center wavelength towards the red, resulting in an increased Stokes shift of 0.46 eV, probably due to the increased strain field. Furthermore, the excitonic binding energy of the alloyed particles was assessed using in situ temperature-dependent photoluminescence measurements, providing insights into the self-trapped exciton mechanism.
Our synthesis produced Cs2KInCl6 nanoparticles with a red-shifted central emission peak at 560 nm, unlike the reported Cs2KInCl6, which exhibits an emission peak at only 495 nm in both nano and bulk forms [1] [2].
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 949682- ERC and from the Israel Science Foundation under grant agreement No 890015. we thank The Helen Diller Quantum Center-Technion.
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