Energy and Charge Transfer Dynamics in Red-Emitting Hybrid Organo-Inorganic Mixed Halide Perovskite Nanocrystals.

We report time-resolved spectral properties of highly stable and efficient red-emitting hybrid perovskite nanocrystals with the composition FA0.5MA0.5PbBr0.5I2.5 (FAMA PeNC) synthesized by using the hot-addition method. The PL spectrum of the FAMA PeNC shows a broad asymmetric band covering 580 to 760 nm with a peak at 690 nm which can be deconvoluted into two bands corresponding to the MA and FA domains. The interactions between the MA and FA domains are shown to affect the relaxation dynamics of the PeNCs from the subpicosecond to tens of nanoseconds scale. Time-correlated single-photon counting (TCSPC), femtosecond PL optical gating (FOG), and femtosecond transient absorption spectral (TAS) techniques were employed to study the intercrystal energy transfer (photon recycling) and intracrystal charge transfer processes between the MA and the FA domains of the crystals. These two processes are shown to increase the radiative lifetimes for the PLQYs exceeding 80%, which may play a key role in enhancing the performance of PeNC-based solar cells.

Effects of Sonication and Hydrothermal Treatments on the Optical and Chemical Properties of Carbon Dots.

In our study, we have tested the effects of sonication and hydrothermal treatments on the properties of carbon dots synthesized from a microwave-assisted method (C-dotsMW). When the carbon dots are sonicated in an aerobic environment, the fluorescence quantum yield decreases drastically because the molecular fluorophores attached to the surface of the carbon dots are oxidized during the sonication process. Meanwhile, the sonicated C-dotsMW also lose their Hg2+ ion sensing and photoreduction activity due to the oxidization of surface functional groups. After the hydrothermal treatment, the fluorescence quantum yield of C-dotsMW increases due to the formation of new fluorophores; however, the Hg2+ ion sensitivity and photoreduction activity of C-dotsMW decrease significantly due to the oxidization of surface functional groups. By autoclaving the C-dotsMW at 100 °C, we have demonstrated that we can enhance the fluorescence quantum yield of C-dotsMW without losing their Hg2+ ion sensitivity. This finding can be used to improve the fluorescence quantum yield of the fluorescent ion sensor based on C-dots.