High-Performance Quantum Dots with Synergistic Doping and Oxide Shell Protection Synthesized by Cation Exchange Conversion of Ternary-Composition Nanoparticles.

The insertion of cation impurities into quantum dots (QDs) as a dopant has been proved to be an efficient way to tailor their optical, electronic, and magnetic properties; however, the low quantum yield (QY) and poor photostability strongly limit their further applications. We report a strategy to coat a thin oxide shell around the heterovalent doped QDs to enhance their QYs and photostabilities simultaneously. In the case of Ag+-doped CdS QDs, the controlled cation exchange reaction between Cd2+ and ternary Ag3SbS3 nanoparticles not only realizes the Ag+ doping in CdS QDs but also generates a thin Sb2O3 shell around the surface of the QDs. Enabled by such, as-prepared CdS:Ag@Sb2O3 QDs exhibited enhanced photostability and high QY of 66.5%. We envision that the findings presented here will inspire more novel protocols for advancing the practical applications of doped QDs.

Near-Infrared Luminescent Ternary Ag3 SbS3 Quantum Dots by in situ Conversion of Ag Nanocrystals with Sb(C9 H19 COOS)3.

Differently from the normal three single precursor method to produce colloidal ternary quantum dots (QDs), herein ternary Ag3 SbS3 quantum dots (QDs) with efficient near-infrared (NIR) luminescence have been prepared by a new facile in situ conversion of Ag nanocrystals (NCs) with a binary Sb/S organic precursor Sb(C9 H19 COOS)3 under low temperature. The unprecedented construction evolution from Ag NCs to Ag3 SbS3 /Ag hetero-structure and final monodisperse Ag3 SbS3 QDs has been demonstrated. These novel Ag3 SbS3 QDs exhibit efficient NIR emission at ≈1263 nm and possess high colloidal stability.

From Indium-Doped Ag2 S to AgInS2 Nanocrystals: Low-Temperature In Situ Conversion of Colloidal Ag2 S Nanoparticles and Their NIR Fluorescence.

Focusing on ternary I-III-VI2 colloidal nanocrystals (NCs) synthesized with precise control of the composition (from doping to ternary composition) and NIR fluorescence performance, monodisperse binary In3+ -doped Ag2 S NCs and ternary AgInS2 NCs have been achieved successfully by facile low-temperature in situ conversion of colloidal Ag2 S nanoparticles. In3+ ions were inserted into the crystal lattice of Ag2 S NCs at a relatively low temperature as dopant and ternary AgInS2 NCs were obtained at a higher temperature following a phase transition. These doped Ag2 S and AgInS2 NCs based on different indium precursor concentrations were explored with respect to the position and intensity of the near-infrared photoluminescent emission at different doping levels and crystal phase evolution.

Excitonic pathway to photoinduced magnetism in colloidal nanocrystals with nonmagnetic dopants.

Electronic doping of colloidal semiconductor nanostructures holds promise for future device concepts in optoelectronic and spin-based technologies. Ag+ is an emerging electronic dopant in III-V and II-VI nanostructures, introducing intragap electronic states optically coupled to the host conduction band. With its full 4d shell Ag+ is nonmagnetic, and the dopant-related luminescence is ascribed to decay of the conduction-band electron following transfer of the photoexcited hole to Ag+. This optical activation process and the associated modification of the electronic configuration of Ag+ remain unclear. Here, we trace a comprehensive picture of the excitonic process in Ag-doped CdSe nanocrystals and demonstrate that, in contrast to expectations, capture of the photohole leads to conversion of Ag+ to paramagnetic Ag2+. The process of exciton recombination is thus inextricably tied to photoinduced magnetism. Accordingly, we observe strong optically activated magnetism and diluted magnetic semiconductor behaviour, demonstrating that optically switchable magnetic nanomaterials can be obtained by exploiting excitonic processes involving nonmagnetic impurities.

Heterovalent Doping in Colloidal Semiconductor Nanocrystals: Cation-Exchange-Enabled New Accesses to Tuning Dopant Luminescence and Electronic Impurities.

Heterovalent doping in colloidal semiconductor nanocrystals (CSNCs), with provisions of extra electrons (n-type doping) or extra holes (p-type doping), could enhance their performance of optical and electronical properties. In view of the challenges imposed by the intrinsic self-purification, self-quenching, and self-compensation effects of CSNCs, we outline the progress on heterovalent doping in CSNCs, with particular focus on the cation-exchange-enabled tuning of dopant luminescence and electronic impurities. Thus, the well-defined substitutional or interstitial heterovalent doping in a deep position of an isolated nanocrystal has been fulfilled. We also envision that new coordination ligand-initiated cation exchange would bring about more choices of heterovalent dopants. With the aid of high-resolution characterization methods, the accurate atom-specific dopant location and distribution could be confirmed clearly. Finally, new applications, some of the remaining unanswered questions, and future directions of this field are presented.