DOI: https://doi.org/10.29363/nanoge.emlem.2024.011
Publication date: 13th July 2024
Near-infrared (NIR) light-sources are of interest for a variety of applications such as hyperspectral imaging, night vision, telecommunication systems and point-of-care testing. Colloidal quantum dots (QDs) possess interesting properties for NIR optoelectronics thanks to their tunable photoluminescence, solution processability (which also enables mechanically flexible devices), and capability for CMOS integration. Various QD compositions have been investigated, most of them either including Pb or Hg, with the latter holding promise for extending emission beyond the telecommunication C-band. Yet, QDs based on heavy-metals cannot gain approval for optoelectronic applications due to the European Union’s “Restriction of Hazardous Substances” (RoHS) directive. Colloidal indium arsenide QDs are emerging as a promising substitute to heavy-metal containing compositions as they are fully RoHS-compliant and, thanks to recent progress in material synthesis, they can demonstrate stable and highly efficient emission.Here, I will discuss our recent findings on different NIR-emitting QDs, in particular InAs and CdHgSe ones.
Employing InAs QDs coated with a thick ZnSe shell (7 monolayers) we were able to reach a photoluminescence quantum yield approaching 70% at 906 nm. We have used such QDs in a light-emitting diode (LED) obtaining an EQE of 13.3%, a turn-on voltage of 1.5V, and a maximum radiance of 12 Wsr-1m-2. Such results are comparable to state-of-the-art PbS QD LEDs. Furthermore, not only the fabricated LEDs are fully RoHS-compliant but it employs InAs QDs prepared via a synthetic route based on non-pyrophoric, cheap, and commercially available precursors.1-4
Similarly, CdHgSe/ZnCdS nanoplatelets (NPLs) exhibit optical absorption and emission that can be tuned from the visible to the NIR range through both quantum confinement and adjustment of their composition. By finely control their synthetic parameters, we have obtained CdHgSe/ZnCdS NPLs with a photoluminescence quantum yield of 58% at 1300 nm (O-band). NIR-LEDs based on NPLs demonstrate and EQE of 7.5%, a turn-on voltage of 0.95 V, and a maximum radiance of 1 Wsr-1m-2.5-6
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