Template synthesis of silver indium sulfide based nanocrystals performed through cation exchange in organic and aqueous
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School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China School of Optics and Photonics, Beijing Institute of Technology, Beijing 100081, China 3 School of Life Science, Beijing Institute of Technology, Beijing 100081, China 4 Department of Materials Science and Engineering, and Centre for Functional Photonics (CFP), City University of Hong Kong, Hong Kong SAR, China 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 15 July 2020 / Revised: 7 November 2020 / Accepted: 9 November 2020
ABSTRACT Heavy-metal-free silver based I-III-VI semiconductor nanocrystals (NCs), including ternary silver indium sulfide (AgInS2) and derivative quaternary silver indium zinc sulfide (i.e., AgInZn2S4) NCs, possess advantages of low toxicity, and size-tunable band gaps approaching near-infrared spectral range, which make them candidates for use in optoelectronic and biological devices. Herein, we report syntheses of AgInS2 based NCs starting from In2S3 template, which have been performed both in organic and aqueous phase through cation exchange. As a result, ternary silver indium sulfide and quaternary silver indium zinc sulfide NCs are obtained in both organic and aqueous media, and confirmed to be orthorhombic AgInS2 NCs and hexagonal AgInZn2S4 NCs, respectively. Furthermore, the aqueous AgInZn2S4 NCs with red emission and low cytotoxicity are explored for the cancer cell imaging.
KEYWORDS template synthesis, silver indium sulfide based nanocrystals, cation exchange, organic and aqueous media
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Introduction
Semiconductor nanocrystals (NCs) have received a lot of attention due to their useful photophysical properties [1–3], leading to applications in solar cells [4, 5], light-emitting diodes [6–9], displays [10, 11], photodetectors [12], and in bio-imaging [13–17]. While II-VI (i.e., CdS, CdSe, CdTe) and IV-VI (i.e., PbS, PbSe) NCs have been the subject of intensive fundamental studies in the past decades [18–26], their commercialization still faces serious challenge because of toxicity of Cd and Pb elements [27]. Therefore, plenty of efforts have been focused to develop their low-toxic alternatives [14]. Among Cd- and Pb-free NCs, I-III-VI ternary NCs have advantages of low cost and easy processing [28–33]. In particular, AgInS2 based NCs possess size-dependent band gap ranging from 1.54 to 2.85 eV [34–38], Bohr exciton radius of 5.5 nm, which is rather useful for both optoelectronic [39] and biological applications [40]. Although AgInS2 NCs can be synthesized by direct synthetic methods [41–44], where precursors of silver, indium and sulfur are allowed to react simultaneously. For example, Uematsu et al. prepared dot-shaped AgInS2 NCs by directly heating a mixture of metal precursor (silver acetate and indium acetate), sulfur precursor (thiourea) and solvent (oleyamine/1-dodecanethiol) at 200 °C [41]. Seeking for other synthesis routes to prepare AgInS2 NCs with different nanostructures is an important issue for their further high per
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