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Rationalizing and Controlling the Surface Structure and Electronic Passivation of Cesium Lead Halide Nanocrystals
摘要： Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and luminescent properties are challenged by the lability of their surfaces, i.e. the interface of the NC core and the ligand shell. On the example of CsPbBr3 NCs, we model the nanocrystal surface structure and its effect on the emergence of trap states using density functional theory. We rationalize the typical observation of a degraded luminescence upon aging or the luminescence recovery upon post-synthesis surface treatments. The conclusions are corroborated by the elemental analysis. We then propose a strategy for healing the surface trap states and for improving the colloidal stability by the combined treatment with didodecyldimethyl ammonium bromide and lead bromide and validate this approach experimentally. This simple procedure results in robust colloids, which are both highly pure and exhibit high photoluminescence quantum yields of up to 95-98%, retained even after 3-4 rounds of washing.
关键词： trap states,didodecyldimethyl ammonium bromide,luminescence recovery,photoluminescence quantum yields,lead bromide,CsPbBr3 NCs,density functional theory,Colloidal lead halide perovskite nanocrystals,surface structure
更新于2025-09-09 09:28:46
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Trap-Mediated Two-Step Sensitization of Manganese Dopants in Perovskite Nanocrystals
摘要： Halide perovskite nanocrystals hold promise for printable optoelectronic and photonic applications. Doping enhances their functionalities and is being investigated for substituting lead with environmentally friendlier elements. The most investigated dopant is Mn2+ that acts as a color center sensitized by the host excitons. The sensitization mechanism is far from understood and no comprehensive picture of the energy-transfer process has been proposed. Similarly, the role of shallow states - particularly abundant in defect tolerant materials - is still unknown. Here, we address this problem via spectroscopic studies at controlled excitation density and temperature on Mn:CsPbCl3 nanocrystals. Our results indicate a two-step process involving exciton localization in a shallow metastable state that mediates the thermally-assisted sensitization of the Mn2+-emission, which is completely quenched for T<200K. At T≤60K, however, such emission surprisingly reappears, suggesting direct energy-transfer from band-edge states. Electron spin resonance supports this picture revealing the signatures of conformational rearrangements below 70K, possibly removing the potential barrier for sensitization. Our results demystify anomalous behaviors of the exciton-to-Mn2+ energy-transfer mechanism and highlight the role of shallow defects in the photophysics of doped perovskite nanostructures.
关键词： Halide perovskite nanocrystals,energy-transfer,spectroscopic studies,Mn2+ dopants,shallow states
更新于2025-09-09 09:28:46