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.¹ 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,² thanks to recent progress in material synthesis, they can demonstrate stable and highly efficient emission.^3–5

Here, I will discuss our recent findings on different NIR-emitting QDs, in particular InAs and CdHgSe ones. In fact, both InAs/ZnSe and CdHgSe/CdS core-shell QDs can be employed for the fabrication of NIR light-emitting diodes with high external quantum efficiencies (EQE).

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 the employed InAs QDs are prepared via a synthetic route based on non-pyrophoric, cheap, and commercially available precursors.

Similarly,  CdHgSe/CdS 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/CdS 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.^6,7

References

¹ Pradhan, S. et al. Nature Nanotechnology 14, (2019)

² Bahmani Jalali, H. et al. Chemical Society Review 51, 9861–9881 (2022)

³ Zhu, D. et al. Advanced Materials, 2303621 (2023)

⁴ De Franco, M. et al. ACS Energy Letters 7, 3788–3790 (2022)

⁵ Zhu, D. et al. Journal of  the American Chemical Society 144, 10515–10523 (2022)

⁶ Prudnikau, A. et al. Advanced Functional Materials 2310067 (2023)

⁷ Mitrofanov, A. et al. Chemistry of Materials 33, 7693–7702 (2021)