Study of the Partial Ag-to-Zn Cation Exchange in AgInS₂/ZnS Nanocrystals

Abstract

AgInS 2 −ZnS (AIZS) nanocrystals (NCs) were synthesized using a simple one-step approach by heating a Ag/ In/Zn/S solution to 210 °C providing highly tunable photoluminescence (PL). The incorporation of Zn even at low temperatures (∼150 °C) and the increased cation exchange of silver by zinc at higher temperatures strongly influence the optical properties of the resulting NCs. The correlation between synthesis parameters and resulting optical properties provided insights on the growth and stability of ternary and quaternary semiconductors. Systematic investigation with time-resolved spectroscopy showed distinguishable PL behaviors between developing and fully grown AIZS NCs. Attempts to coat as-prepared AgInS 2 NCs resulted in the same PL behavior as the one-step reaction product indicating that Zn readily exchanges with Ag ions even when not directly incorporated in the initial reaction mixture. Even with a low amount of zinc, the fully grown AIZS NCs showed improved PL QYs and single exponential decay behavior with long PL lifetimes. Control of the optical properties of these NCs makes them potentially useful for applications in photovoltaics and bioimaging particularly in light of their nontoxicity.

Thermal decomposition based synthesis of Ag-In-S/ZnS quantum dots and their chlorotoxin-modified micelles for brain tumor cell targeting

“…It is generally agreed that cation exchange between Zn ions (from Zn precursor) with Ag (or Cu) in AIS (or CIS) causes photoluminescence blue shift and QY enhancement. 8, 25–26 As shown in Figure 1(b), we did observed both effects after growing ZnS shell on AIS cores. EDX analysis demonstrates a good match of the observed photoluminescence blue shift and QD brightness enhancement of AIS/ZnS QDs compared to AIS QDs.…”

Heat-up synthesis of Ag–In–S and Ag–In–S/ZnS nanocrystals: Effect of indium precursors on their optical properties

“…The ZnS-coating or zinc etching caused blue-shift is a typical feature of I-III-VI NCs including Cu-In-S (CIS) and Ag-In-S (AIS) NCs. Generally, it is thought that cation exchange between Zn ions (from Zn precursor) with Cu, Ag, or In in NCs occurs during ZnS-coating or zinc etching [11, 16, 20–21]. The cation exchange could etch cores and result in size-reduced cores, which are corresponding to short emission wavelength.…”

“…Since low synthesis temperatures are relatively hard to promote the NC growth in a wide size range, controlling nonstoichiometry (adjusting Ag:In molar ratio in reactions), zinc doping, or a combination of them are major strategies for the tuning of AIS photoluminescence properties [3–18]. Regarding high QYs, they usually can be achieved through ZnS shell growth on NC cores [11, 15–17]. In spite of the progress on the development of high quality AIS NCs, most of the reported synthesis approaches are hot-injection based ones, which have intrinsic limits for NC scalable production.…”

Understanding of the major reactions in solution synthesis of functional nanomaterials

“…So, the increased blue-shift in their emission was believed to be ascribed to the reduced core size. Also, they extended this partly cation exchange to prepare the AgInS2/ZnS core/shell quantum dots, which showed a blue shift of 70 nm in the emission spectra [409]. Agarwal and co-workers [410] used the protocol of size-dependent cation exchange reactions in transformation of composition-controlled single-crystalline nanowires involving the cation exchange between Zn and Cd.…”