The incorporation of paramagnetic, spin-5/2 manganese (Mn) impurities into II–VI colloidal quantum dots (QDs) results in considerable modifications of their optical and magneto-optical properties.(1) In particular, strong sp-d exchange interactions between a semiconductor host and magnetic impurities lead to fast excitation transfer from the QD to the Mn ions, which enables highly efficient emission in the intragap region due to radiative relaxation of the excited Mn state. Recent studies of Mn-doped CdSe QDs demonstrate that energy transfer from an excited Mn ion (Mn*) to carriers residing in QD intrinsic states is extremely fast (~100 fs timescale), which allows for the ejection of a hot electron outside the dot prior to its cooling to the band edge.(2) The estimated energy gain rate reaches very high values of more than 10 eV ps–1, and as a result, it overshoots the energy loss rate by a factor of approximately seven. This is a dramatic departure from the standard situation, which is expected to lead to the spin-exchange driven new phenomena. 

1. J. Am. Chem. Soc. 142, 18160-18173 (2020).

2. Nat. Photon. 16, 433-440 (2022).

In recent years, two-dimensional (2D) transition-metal chalcogenides (TMCs) have emerged as an important class of materials, where the new material properties are obtained by reducing the dimensionality. For instance, the band gap of various semiconducting TMCs changes from an indirect to a direct gap with a concomitant appearance of strong exciton photoluminescence (PL) when they become single-layer thick. In particluar, the valley-selective excitation, providing a new degree of freedom to manipulate the material properties, also becomes possible in single-layer TMCs. Recently, we discovered that the reduction of the lateral size to the nanoscale can potentially combine the unique property of the 2D exciton with additional lateral confinement.(1) It creats the ‘single-layer quantum dot (SQD)’ that is distinctly different from more common QDs derived from 3D crystals.

1. J. Am Chem. Soc. 138, 13253-13259 (2016). 

Charge transfer (CT) is a process wherein the interfacial charge, electron or hole, relocates from a donor to an acceptor. The CT in quantum confined semiconductor nanomaterials have been recognized as a crucial process for light harvesting and solar energy conversion, especially photochemical reactions. Recently, we compared three inorganic surface capping ligands (ICLs) (SnS44–, SbS43– and AsS33–) for the CT process from QDs.(1) In the case of organic capping ligands, it is typically the size of ligand (e.g., alkyl chain length) that critically governs the carrier dynamics. In contrast, the HOMO LUMO energy levels with respect to the QD bands become very important for ICL-QDs. Because ICLs can be exempt from the high energy barrier which is quite inherent for organic ligands, a very efficient charge transfer and collection that exceeds the performance attainable by organic capped QDs can be promised. On the other hand, facilitating or impeding charge transfer pathways enables precise control over PL intensity in QDs, as the transfer of charge from QDs leads to PL quenching. By designing QD-Prussian blue (PB) composites, we leveraged PB’s electroswitchable properties, where applied voltages control the oxidation state of iron ions.(2) These voltages regulate charge transfer pathways, and modulate the interaction between the PB and QDs to achieve precise PL control. 

1. J. Am. Chem. Soc. 137, 13827-13835 (2015).

2. Nano Lett. 25, 11391-11397 (2025).

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