Impurity incorporation and exchange interactions in Co2+-doped CdSe/CdS core/shell nanoplatelets

Abstract

The intentional incorporation of transition metal impurities into colloidal semiconductor nanocrystals allows an extension of the host material's functionality. While dopant incorporation has been extensively investigated in zero-dimensional quantum dots, the substitutional replacement of atoms in two-dimensional (2D) nanostructures by magnetic dopants has been reported only recently. Here, we demonstrate the successful incorporation of Co 2+ ions into the shell of CdSe/CdS core/shell nanoplatelets, using these ions (i) as microscopic probes for gaining distinct structural insights and (ii) to enhance the magneto-optical functionality of the host material. Analyzing interatomic Co 2+ ligand field transitions, we conclude that Co 2+ is incorporated into lattice sites of the CdS shell, and effects such as diffusion of dopants into the CdSe core or diffusion of the dopants out of the heterostructure causing self-purification play a minor role. Taking advantage of the absorption-based technique of magnetic circular dichroism, we directly prove the presence of sp-d exchange interactions between the dopants and the band charge carriers in CdSe/Co 2+ :CdS heteronanoplatelets. Thus, our study not only demonstrates magneto-optical functionality in 2D nanocrystals by Co 2+ doping but also shows that a careful choice of the dopant type paves the way for a more detailed understanding of the impurity incorporation process into these novel 2D colloidal materials.Published under license by AIP Publishing. https://doi. ARTICLEscitation.org/journal/jcp 76 J. A. Gaj and J. Kossut, "Basic consequences of sp-d and d-d interactions in

2D II–VI Semiconductor Nanoplatelets: From Material Synthesis to Optoelectronic Integration

“…392 In such situations, it is possible to distinguish between electron and hole trapping signals, as core/shell CdSe/CdS NPLs suppress hole trapping but not electron trapping. 392 In addition to this paramagnetic behavior from dangling bonds, doping of CdE NPLs with transition metals, such as manganese, 141,304−306 cobalt, 142 and silver 394 also generates diluted magnetic behavior. The magnetic dopants can be localized in a specific layer of core and shell structures.…”

“…In addition to this paramagnetic behavior from dangling bonds, doping of CdE NPLs with transition metals, such as manganese, ,− cobalt, and silver also generates diluted magnetic behavior. The magnetic dopants can be localized in a specific layer of core and shell structures .…”

“…Doping in the shell of Mn- and Co-doped core/shell NPLs does not substantially change the emission spectrum. However, dopants induce stronger magnetic circular dichroism responses than undoped controls. ,,, In the case of silver dopants, photoexcitation induces paramagnetic behavior due to the presence of unbound electrons …”

“…c-ALD enables a discrete stepwise progression of core/shell structures while maintaining the atomic precision of the NPL building blocks. ,, Using different metals or chalcogenides precursors, several core/shells structures have been successfully synthesized: CdSe/ZnS, , CdSe/ZnSe, CdSe/CdS, ,,, CdSe/Cd x Zn 1– x S, ,,, CdTe/CdS, and CdTe/CdSe span the entire visible spectrum, CdS/ZnS covers the blue spectral window, and CdSe/HgSe and Cd x Hg 1– x Se/CdSe have bandgap energies in the near-infrared . It is also highly desirable to dope the shell with magnetic impurities, including manganese or cobalt. , However, the fluorescence quantum yields for heterostructures grown at low temperatures using c-ALD do not match those reported for high-temperature synthesis. This is likely due to defects that appear at the core/shell interface and in the shell during room temperature growth .…”

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

“…Generally, impurity-doped nanocrystals can exhibit not only the intrinsic merits of nanocrystals but also additional advantages including enhanced thermal and chemical stability, improved photoluminescence quantum efficiency (PLQY), reduced Auger recombination, impurity-related emission, and tailored charge mobility [ 59 , 60 , 61 , 62 , 63 ]. Owing to these superiorities, impurity-doped nanocrystals have sparked efforts to satisfy the requirement of many optoelectronic applications.…”