Exciton Energy Shifts and Tunable Dopant Emission in Manganese-Doped Two-Dimensional CdS/ZnS Core/Shell Nanoplatelets

Abstract

The ability to dope transition-metal ions into semiconductor nanocrystals (NCs) allows for the introduction and exploitation of new extrinsic properties in the original intrinsic material. Although the synthesis of doped zero-dimensional quantum dots and one-dimensional nanorods/nanowires has been widely reported, transition-metal ion-doped two-dimensional (2D) NCs have been less explored. In this study, we developed a one-pot synthesis of Mn 2+ -doped 2D CdS (i.e., Mn:CdS) nanoplatelets (NPLs). Successful Mn doping inside the CdS NPL lattice was confirmed by electron paramagnetic resonance and X-ray diffraction measurements. Surprisingly, only CdS photoluminescence (PL), without contribution from Mn PL, was observed in the Mn:CdS NPLs, regardless of Mn doping concentration. To address the issue of poor thermal stability and improve the optical properties of the 2D Mn:CdS NPLs, we synthesized ZnS shell-passivated Mn:CdS/ZnS core/shell NPLs using a single-source shelling precursor method, which allows for ZnS surface passivation of NPLs at relatively low temperatures, while being thermally adaptable to ensure minimal NPL degradation. An extremely large exciton red shift (∼420 meV), upon ZnS shell passivation, was observed because of the increased effective thickness of the CdS core NPLs. Steady-state and time-resolved emission measurements indicate that the host−dopant energy-transfer efficiency and Mn−Mn interactions within the 2D Mn:CdS/ZnS core/shell NPLs can be fine-tuned via the dopant concentration, resulting in an intense Mn PL as well as tunable dual-band emission from the host NPLs and Mn dopants. Magnetic measurements indicate intrinsic spin states in the 2D NPLs and complex magnetic interactions at high doping concentrations, including antiferromagnetic exchange between dopants and possible dopant−surface state interaction.

Record High External Quantum Efficiency of 19.2% Achieved in Light‐Emitting Diodes of Colloidal Quantum Wells Enabled by Hot‐Injection Shell Growth

“…Despite the PL emission peaks being almost the same (i.e., 639 and 644 nm for core/c‐ALD and core/HIS CQWs, respectively), the PLQY of CdSe/Cd 0.25 Zn 0.75 S core/c‐ALD shell is only 10%, leading to the poor device efficiency . However, it is deserved to point out that such PLQY is consistent with that of reported core/shell CQWs utilizing c‐ALD, with levels in the range of 0.5–11% . The XRD and XPS characterizations of the CdSe/Cd 0.25 Zn 0.75 S core/c‐ALD and core/HIS are shown in Figures c,d, respectively.…”

Optically detected magnetic resonance in CdSe/CdMnS nanoplatelets

“…Doping with magnetic ions has been successfully realized for colloidal NCs, where the characteristic DMS properties have been observed for spherical quantum dots (QDs), [8][9][10][11][12][13][14] nanoribbons, 15,16 and NPLs. [17][18][19][20][21][22] Optically detected magnetic resonance (ODMR) is a powerful technique for investigating the electronic and spin struc-ture of semiconductors and their nanostructures, for a review see ref. [24][25][26].…”

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

“…Excitons are generated for radiative recombination when electrons and holes meet each other in the EML, leading to the intentional emissions based on the used emitters. To guarantee excitons being radiatively decayed, the nonradiative channels (e.g., Auger recombination) should be avoided [ 167 , 168 , 169 ]. In particular, charge imbalance is harmful to the device performance [ 170 , 171 , 172 , 173 , 174 ].…”