Bandgap‐ and Radial‐Position‐Dependent Mn‐Doped Zn–Cu–In–S/ZnS Core/Shell Nanocrystals

Abstract

This paper presents a mechanistic study on the doping of Zn-Cu-In-S/ZnS core/shell quantum dots (QDs) with Mn by changing the Zn-Cu-In-S QD bandgap and dopant position inside the samples (Zn-Cu-In-S core and ZnS shell). Results show that for the Mn:Zn-Cu-In-S/ZnS system, a Mn-doped emission can be obtained when the bandgap value of the QDs is larger than the energy of Mn-doped emission. Conversely, a bandgap emission is only observed for the doped system when the bandgap value of QDs is smaller than the energy gap of the Mn-doped emission. In the Zn-Cu-In-S/Mn:ZnS systems, doped QDs show dual emissions, consisting of bandgap and Mn dopant emissions, instead of one emission band when the value of the host bandgap is larger than the energy of the Mn-doped emission. These findings indicate that the emission from Mn-doped Zn-Cu-In-S/ZnS core/shell QDs depends on the bandgap of the QDs and the dopant position inside the core/shell material. The critical bandgap of the host materials is estimated to have the same value as the energy of the Mn d-d transition. Subsequently, the mechanism of photoluminescence properties of the Mn:Zn-Cu-In-S/ZnS and Zn-Cu-In-S/Mn:ZnS core/shell QD systems is proposed. Control experiments are then carried out by preparing Mn-doped Zn(Cu)-In-S QDs with various bandgaps, and the results confirm the reliability of the suggested mechanism. Therefore, the proposed mechanism can aid the design and synthesis of novel host materials in fabricating doped QDs.

Ligand Engineering for Mn2+ Doping Control in CsPbCl3 Perovskite Nanocrystals via a Quasi-Solid–Solid Cation Exchange Reaction

“…We hypothesize that the Mn 2+ is initially doped heterogeneously throughout the perovskite lattice immediately following the cation exchange, more specifically localized around the surface of the NCs. Radial positioning of Mn 2+ dopants has been heavily studied in other quantum dot systems and has been found to alter resulting NC properties. − Additionally, Mn 2+ doping in CsPbCl 3 NCs through cation exchange has been previously shown to initially result in heavily surface doped NCs, also affecting the optical properties . In our system, initial heterogeneous surface doping is supported by the red-shifted Mn 2+ emission peak (625 nm) compared to a majority of previously reported values (585–600 nm) (Figure A). ,, In fact, red-shifted Mn 2+ emission peaks in Mn 2+ -doped CsPbCl 3 NCs have only been reported in cases with high dopant concentrations (7–15%) as a result of strong Mn 2+ –Mn 2+ interactions which decrease the energy difference between the Mn 2+ 4 T 1g and 6 A 1g electronic states. , This red-shift in NCs with high Mn 2+ doping level is also usually accompanied by a blue-shift in the BG emission peak position by as large as 13 nm as a result of “BX 6 ” octahedra contraction and alloying effects. ,, The 625 nm Mn 2+ emission that we observed, however, was not coupled with a significant blue-shift in BG emission (only ∼1 nm), which suggests that the Mn 2+ dopants experience strong Mn 2+ –Mn 2+ interaction despite the lack of octahedral contraction supported by XRD measurements (Figure A,B).…”

Mn-Doped Quinary Ag–In–Ga–Zn–S Quantum Dots for Dual-Modal Imaging

“…Usually, the Mn-related emission is attributed to the radiative transition from the low-spin excited state of Mn 2+ ( 4 T 1 ) to its high-spin ground state ( 6 A 1 ). This emission is observed for CIZS or AIZS QDs with an energy band gap larger than that of this Mn 2+ -related transition energy (dual D–A and Mn emissions can also be observed). ,,− On the contrary, only the D–A emission is observed when the host QDs exhibit a band gap smaller than the Mn emission. ,, These results will be discussed below in the case of AIGZS QDs.…”

Human Umbilical Cord Wharton’s Jelly-Derived Mesenchymal Stem Cells Labeled with Mn2+ and Gd3+ Co-Doped CuInS2–ZnS Nanocrystals for Multimodality Imaging in a Tumor Mice Model

“…27 The absence of distinct absorption is generally attributed to inhomogeneous distribution in multidopant and multinary NCs. 29 Interestingly, the DDT-functionalized CIS NCs exhibited PL emission at 640 nm with reduced PL QY of 19% and PL lifetime of 10.4 μS, whereas after nanoalloying with ZnS, the PL emission was shifted to 624 nm with enhanced PL QY of 56.77% and PL lifetime of 14.2 μS. The substantial enhancement in PL is ascribed to passivation of CIS NCs resulting in reduced surface defects responsible for nonradiative recombinations.…”

“…28 Also, Peng et al reported dual-emissions in CuInS 2 −Mn/ZnS NCs. 29 However, these empirical reports are still unclear regarding the dopant position inside or on the surface of CIZS NCs in relation with optical properties for bioimaging applications. This disparity generally occurs owing to the reactivity of the cationic precursor resulting in the phase separation.…”

“…However, Ding et al reported distinct band-edge emissions in CuInS 2 /Mn/ZnS NCs, instead of Mn-doped emission . Also, Peng et al reported dual-emissions in CuInS 2 –Mn/ZnS NCs . However, these empirical reports are still unclear regarding the dopant position inside or on the surface of CIZS NCs in relation with optical properties for bioimaging applications.…”