Colloidal infrared (IR) emitting semiconductor nanocrystals (NCs) are showing great potential in numerous fields, including light-emitting diodes (LEDs), photovoltaics, night vision devices, optical communication systems, lasers, and biological imaging. The most developed colloidal NC compounds for IR are lead (Pb) (IV-VI) and mercury (Hg)-based (II-VI) chalcogenides, however, owing to their toxicity issues, they are not compliant with the EU’s ‘Restrictions of Hazardous Substances’ (RoHS) directive. In contrast to these materials, heavy-metal-free III-V indium arsenide (InAs) colloidal NCs have emerged as ideal candidates due to their adjustable optical bandgap in the short-wave-infrared (SWIR) spectral range and compliance with RoHS standard[1].

To date, several arsine-based precursors such as tris-trimethylsilyl arsine (TMS-As) and tris-trimethylgermyl arsine (TMGe-As) have been employed to synthesize InAs colloidal NCs[2, 3]. However, high pyrophoricity, inherent toxicity, and high-cost issues of these precursors limit their usage in the synthesis of InAs NCs. Recently, tris(dimethylamino)-arsine (amino-As) has attracted great attention as an alternative arsenic source compared to its counterparts due to it being less hazardous, cheaper, and commercial availability. Nevertheless, it is required to employ a reducing agent in the production of InAs NCs based on amino-As to facilitate As-3 formation and promote nucleation. Of the various studies published so far, several reducing agents with different strengths have been introduced, including alane N,N dimethylethylamine complex (DMEA-AlH3), diisobutylaluminum hydride (DIBAL-H), lithium triethylborohydride (LiEt3BH), and trioctylamine alane (TOA-AlH3). However, the rapid depletion of monomers during the synthesis process limits further growth of NCs. To address this issue, different continuous injection techniques were employed by several groups. In this regard, Kim et al. showed InAs NCs with an first excitonic peak at ~1600 nm by contiuous injection of InAs cluster solution into the InAs seed at elevated temperature[4]. Similarly, Franke et al. synthesized SWIR emitting InAs-based core@shell NCs by slow injection of TMGe-As[5]. More recently, Panda et al. synthesized amino-As based InAs@ZnSe NCs which can emit up to 1400 nm with high photoluminescence efficiency by continuous injection[6]. Considering the approaches thus far, one-pot production of larger colloidal NCs with emission wavelengths in the SWIR range (> 1000 nm) remains challenging.

In our study, we introduce a one-pot approach to synthesize SWIR InAs-based core and core@shell NCs. In this regard, we have used a new reducing agent which enables the controlled growth of InAs core NCs, tuning the absorbance (Abs) from 835 to 1165 nm. Then, without any purification step, we grew zinc selenide (ZnSe) shell on bare core structure to increase photoluminescence quantum yield (PLQY). The resulting core@shell NCs exhibited PLQY values of ~46%, ~19%, and ~8% at ~1030, ~1080, and ~1500 nm emission wavelengths, respectively.

Keywords: Indium arsenide, reducing agent, one-pot synthesis, colloidal, quantum dots, nanocrystals