Abstract
We introduce a direct aqueous synthesis of luminescent 2–3 nm Ag–In–Se (AISe) quantum dots (QDs) capped by glutathione (GSH) complexes, where sodium selenosulfate Na2SeSO3 is used as a stable Se2− precursor. A series of size-selected AISe QDs with distinctly different positions of absorption and PL bands can be separated from the original QD ensembles by using anti-solvent-induced size-selective precipitation. The AISe–GSH QDs emit broadband PL with the band maximum varying from 1.65 eV (750 nm) to 1.90 eV (650 nm) depending on the average QD size and composition. The PL quantum yield varies strongly with basic synthesis parameters (ratios of constituents, Zn addition, duration of thermal treatment, etc.) reaching 4% for “core” AISe and 12% for “core/shell” AISe/ZnS QDs. The shape and position of PL bands is interpreted in terms of the model of radiative recombination of a self-trapped exciton. The AISe–GSH QDs reveal phonon Raman spectra characteristic for small and Ag-deficient tetragonal Ag–In–Se QDs. The ability of ultra-small AISe QDs to support such “bulk-like” vibrations can be used for future deeper insights into structural and optical properties of this relatively new sort of QDs.
Highlights
Multinary indium-based metal chalcogenide quantum dots (QDs), in particular, copper indium sul de/selenide CuInS(Se)[2] (CIS/CISe) and silver indium sul de/selenide AgInS(Se)[2] (AIS/ AISe), have revealed a number of outstanding structural and optical properties, different from both binary metal–In-based ternary QDs can emit strong PL which combines a broadband character and relatively large lifetimes with high intensity and distinct dependence on the QD size and composition
We discuss the optimization of the synthetic protocol to achieve the highest PL quantum yield (PL quantum yield (QY)) through variations of the nominal ratio of AgI to InIII, duration of the thermal treatment tH, and ratios of SS to AgI, and ZnII to AgI, as well as size-dependent optical characteristics of AISe QDs produced by the size-selective precipitation/redispersion
We present a survey of vibrational characteristics of AISe QDs probed by Raman spectroscopy at room and low temperatures
Summary
Multinary indium-based metal chalcogenide quantum dots (QDs), in particular, copper indium sul de/selenide CuInS(Se)[2] (CIS/CISe) and silver indium sul de/selenide AgInS(Se)[2] (AIS/ AISe), have revealed a number of outstanding structural and optical properties, different from both binary metal–. In-based ternary QDs can emit strong PL which combines a broadband character and relatively large lifetimes (several hundred ns) with high intensity and distinct dependence on the QD size and composition. The combination of the broad variability of PL properties, high PL QYs, stability, and comparatively low toxicity of ternary QDs has inspired numerous studies aimed to shi the PL emission to the near-infrared (NIR) spectral range, that is, to the rst “transparency window” of bio-tissues required, in particular, for in vivo luminescent biosensing applications.[2,8,9,11,12] Reducing the bandgap of QD emitters by exchanging S for Se is apparently the most straightforward solution, the challenge of maintaining a reasonably high PL QY for the NIR-. The high absorption coefficients and the variability of the absorption band parameters of AISe QDs as well as the broad tunability of the positions of conduction band (CB)
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