The photophysical properties of core/shell semiconductor nanocrystals are influenced by the shell thickness as well by the surface, whether it is cationic or anionic. In this work, we have investigated the effect of thickness of shell as well as the surface terminating layeranionic and cationicon the optical properties in CdSe/CdS which is a quasi-type-II system and CdSe/ZnS, a type-I heterostructured core/shell nanoplatelets (NPLs). The results reveal that no matter which cation is on the surface – Zn or Cd–the photoluminescence (PL) is always high compared to the surface being anion terminated. An alternating behavior in the PL intensity is observed upon successively terminating the surface with cations and anions, which has been achieved using the colloidal atomic layer deposition (cALD) technique. Not only the PL intensity but also the PL lifetimes and the emission peak widths too follow this similar alternating trend. All of these can be simply explained on the basis of the trap states that are created on the surface depending upon cation or anion termination.

We show that the colloidal growth of SnS nanosheets (NS), a group IV metal chalcogenide (MC), on MoSe2 NS, a transition metal dichalcogenide (TMDC), results in the formation of type-II nanoheterostructures (NHS). The MoSe2/SnS NHS synthesis is accompanied by in situ generation of MoO3–x at the MoSe2 and SnS interface activating the otherwise electrochemically inert basal planes of MoSe2 NS. The MoSe2/SnS NHS exhibit more active sites, and the built-in electric field at the interface enhances the rate of charge transfer. The largely enhanced electrocatalytic activities are attributed to the electronic property manipulation due to the synergistic interactions between MoSe2 NS and SnS NS. This work provides insights into the design of multicomponent low-dimensional 2D/2D (D = dimension) NHS based on TMDC/MC combination with enhanced electrochemical properties, in particular for applications of water splitting.

The synthesis of core/crown heterostructures allows us to modify the properties of nanoplatelets (NPLs) by altering the lateral dimensions without affecting their thickness, that is, the confinement direction. We have presented the synthesis and study of photophysical properties of type-II CdS/ ZnSe core/crown NPLs, where electron-wave function is confined to CdS core, while hole wave function resides in ZnSe crown. The recombination of the photogenerated excitons in CdS and ZnSe occurs across the interface of both semiconductors and due to which the emission shows a red shift of ∼100 nm. The lifetime of CdS/ZnSe increases almost two orders of magnitude in comparison with the core CdS NPLs. The fast decaying excited states of the NPLs are distributed over the CdS/ZnSe interface and slow down; the larger lifetimes allow for their potential utilization in applications requiring charge separation.

Lanthanide ions (Ln3+) are well-known dopants for controlling the optoelectronic properties of double perovskites (DPs). However, the excitation energy of Ln3+-doped Cs2AgInCl6 being too high (∼250–290 nm) limits its direct excitation by commercial UV light-emitting diodes (≥365 nm). To overcome this challenge, we employed Bi3+ as a sensitizer to induce the emission of Sm3+ at much lower excitation energy in Sm3+–Bi3+ codoped Cs2AgInCl6 DP nanocrystals (NCs). Spectral analysis shows that a trace amount of Bi3+ (∼1%) doping provides dual emission of self-trapped excitons (STEs) and characteristic emissions of Sm3+ assigned to 4G5/2 to 6H J (J = 5/2, 7/2, 9/2, and 11/2) transitions with 368 nm excitation energy. Transient absorption spectroscopic results revealed the existence of nonradiative energy transfer from STE states. Subsequently, we propose a mechanism to explain the formation of energy-transfer channels from STEs to excited states of Sm3+. Our study demonstrates that Bi3+ can efficiently sensitize Sm3+ to modify the optical properties of lead-free DP NCs to expand their luminescence application.

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