Ultra-Confined Visible-Light-Emitting Colloidal Indium Arsenide Quantum Dots

Abstract

Indium arsenide quantum dots, which typically emit in the near-infrared, have been utilized in various optoelectronics and biomedical applications, such as covert illumination, optical communication, and deep-tissue imaging. While theory predicts that further quantum confinement through size reduction could enable visible light emission, systems with larger optical bandgaps have not been realized. Here, we report a method of preparing highly luminescent, visible-light-emitting In(Zn)As/ZnSe/ZnS QD, using a low-temperature nanocluster synthesis approach. Each QD contains an ultraconfined In(Zn)As nanocluster and fluoresces at tunable wavelengths between 538 and 640 nm with a high photoluminescence quantum efficiency of 58%. We confirm, through DFT and spectroscopic analysis, that the strong confinement effects in the few-atom-wide In(Zn)As nanoclusters are responsible for the significant spectral shift from the nearinfrared to the visible region. These findings suggest that broader-than-expected optical tuning may now be achievable in other quantum-confined semiconductor systems, which could lead to a wider scope of functional applications in optoelectronics.

ZnCl2 Mediated Synthesis of InAs Nanocrystals with Aminoarsine

“…34,35 Additionally, the PL quantum yields (QYs) characterizing Cd-free InAs-based core@shell NCs made with TMS-As/TMGe-As, such as InAs@InP@ZnSe NCs, can be as high as 23%, while those synthesized with amino-As (i.e., InAs@ZnSe or InAs@ZnS) could only reach ∼10%. 14,26,30,31 It was noted that ZnCl 2 has been extensively used as an additive in the synthesis of InAs NCs based on amino-As and amino-P, the latter acting as a mild reducing agent. ZnCl 2 is actually believed to trigger the NCs formation by activating the amino-P reducing agent, which would not work otherwise.…”

“…Semiconductor nanocrystals (NCs) emitting in the infrared spectral region are very appealing building blocks for applications ranging from telecommunications to night vision, photovoltaics, , lasing, and in vivo biological imaging. , To date, the most studied near-infrared (NIR) and short-wave infrared emitting NC compounds are Hg-based (II–VI) or Pb-based (IV–VI) semiconductors, whose synthesis and optical properties have been optimized over the past decades. − The presence of Hg or Pb, however, severely restricts the use of such compounds in commercial applications due to the EU’s “Restriction of Hazardous Substances” (RoHS) directives, prompting the search for alternative lead- and mercury-free RoHS compliant materials. − Among the possible candidates, III–V semiconductors, in particular InAs NCs, have been indicated as the most appealing alternatives. , One important reason is that the absorption and photoluminescence (PL) of InAs NCs can be tuned from 750 to 1400 nm, thus covering a large fraction of the NIR range with a single material. However, the synthesis of InAs is far more complex than that of the more studied II–VI and IV–VI NCs.…”

“…Yet, improvements are still needed to meet the standards reached with the TMS-As/TMGe-As precursors. For example, the width of the first exciton absorption peak (normally measured as half width at half-maximum, HWHM) of InAs NCs, which is strictly correlated to the size distribution of the sample, can be as narrow as 60 meV or even 40 meV when employing TMS-As/TMGe-As, while in the case of amino-As the best value reported so far is around 100 meV. , Additionally, the PL quantum yields (QYs) characterizing Cd-free InAs-based core@shell NCs made with TMS-As/TMGe-As, such as InAs@InP@ZnSe NCs, can be as high as 23%, while those synthesized with amino-As (i.e., InAs@ZnSe or InAs@ZnS) could only reach ∼10%. ,,, …”

Wurtzite InAs Nanocrystals with Short-Wavelength Infrared Emission Synthesized through the Cation Exchange of Cu3As Nanocrystals

“…Among the group III–V semiconductors, bulk indium arsenide (InAs) is a direct semiconductor with a narrow bulk band gap of ∼0.35 eV . Colloidal InAs NCs exhibit widely tunable emitting wavelengths ranging from the visible region to the short-wavelength infrared (SWIR, 1000–2000 nm) region by size adjustment and stand out as an infrared-active candidate material for efficient SWIR LEDs, biological imaging, photovoltaics, and sensing applications. ,, InAs in bulk is known to crystallize into two distinct phases, a stable cubic zinc-blende phase and a metastable high-temperature hexagonal wurtzite phase. , Compared to the zinc-blende structure with T d point group symmetry, the characteristic feature of the wurtzite structure ( C 6 v point group symmetry) is the crystal field, causing the formation of three doubly-degenerate hole bands at the topmost valence band when combining with the spin–orbit interaction .…”

“…15−18 Among the group III−V semiconductors, bulk indium arsenide (InAs) is a direct semiconductor with a narrow bulk band gap of ∼0.35 eV. 19 Colloidal InAs NCs exhibit widely tunable emitting wavelengths ranging from the visible region to the short-wavelength infrared (SWIR, 1000−2000 nm) region by size adjustment and stand out as an infrared-active candidate material for efficient SWIR LEDs, biological imaging, photovoltaics, and sensing applications. 6,12,20 InAs in bulk is known to crystallize into two distinct phases, a stable cubic zinc-blende phase and a metastable high-temperature hexagonal wurtzite phase.…”