Lead‐free halide perovskite nanocrystals (NCs) with the unique optical properties are of interest for broad applications. There are a few studies on near‐infrared (NIR) emission in perovskite NCs. Here, all‐inorganic rare‐earth‐based Cs2NaEr1−xBxCl6 (B: In, Sb, or Bi; x = 0, 0.13, and 0.5) double perovskite (DP) NCs have been successfully sythesized. The Cs2NaErCl6 NCs show good air stability and emit a sharp NIR photoluminescence (PL) at telecommunication wavelength of 1543 nm, originating from 4I13/2→4I15/2 transition of the Er3+, and its average lifetime is 35.7 µs. Especially for Cs2NaEr0.5Sb0.5Cl6 NCs, NIR PL can be enhanced 23‐fold with the lifetime being 119.1 µs. Moreover, femtosecond transient absorption measurements prove that a long‐lifetime trap state promotes NIR emitting in the mixed Sb/Er DP NCs.

The investigation of biexciton dynamics in single colloidal quantum dots (QDs) is critical to biexciton-based applications. Generally, a biexciton exhibits an extremely low photoluminescence (PL) quantum yield as well as very fast PL decay due to strong nonradiative Auger recombination, making it difficult to investigate the biexciton dynamics. Here, we develop a quantitative method based on intensity- and time-resolved photon statistics to investigate the biexciton dynamics in single colloidal QDs. This robust method can be used under high-excitation conditions to determine the absolute radiative and Auger recombination rates of both neutral and charged biexciton states in a single QD level, and the corresponding ratios between the two states agree with the theoretical predictions of the asymmetric band structures of CdSe-based QDs. Furthermore, the surface traps are found to provide additional nonradiative recombination pathways for the biexcitons, and their contributions are quantified by the method.

We present a method to modulate the fluorescence of non-polar single squaraine-derived rotaxanes molecules embedded in a polar poly(methyl methacrylate) (PMMA) matrix under an external electric field. The electron transfer between single molecules and the electron acceptors in a PMMA matrix contributes to the diverse responses of fluorescence intensities to the electric field. The observed instantaneous and non-instantaneous electric field dependence of single-molecule fluorescence reflects the redistribution of electron acceptors in PMMA induced by electronic polarization and orientation polarization of polar polymer chains in an electric field.

Charge and energy transfer dynamics in Colloidal CdSeTe/ZnS quantum dots (QDs)/monolayer molybdenum disulfide (MoS2) heterostructures have been investigated by time-resolved single-dot photoluminescence (PL) spectroscopy. Time-gated method is used to separate...

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