Zinc-Free Synthesis of High-Quality Indium Phosphide Quantum Dots Covering a Large Size Range

Indium phosphide QDs hold great promises for use in displays and LEDs and are widely considered a safer alternative to toxic Cd-based QDs.[1] Even though significant progress has been made in their synthesis, using non-pyrophoric phosphorus precursors it is still highly challenging to achieve narrow emission linewidths and to reach the near-infrared spectral range. The addition of zinc carboxylates to the synthesis of InP QDs has become commonplace with the goal to reduce the size distribution and increase the PLQY [2]. However, lattice doping by zinc can lead to shallow hole traps inducing spectral broadening, large Stokes shift, and long PL lifetimes.[3]<br/><br/>We present a novel Zn-free synthetic pathway for high-quality InP QDs. As-synthesized InP QDs are tetrahedral-shaped with tunable sizes from 3 nm to 9 nm without secondary additions of precursors. The first excitonic is tunable from 450 nm to 700 nm by changing the reaction conditions. These core QDs have been subsequently overcoated with a thin ZnS shell at a temperature as low as 140°C to avoid alloying and doping of the core lattice. The emission of the InP/ZnS QDs was tunable up to 728 nm with a NIR PL linewidth of only 48 nm (FWHM). The obtained InP/ZnS QDs also exhibit a much lower Stokes shift and significantly shorter PL lifetime compared to the reported data. Finally, the reaction mechanism underlying the novel synthetic scheme was elucidated by NMR spectroscopy.<br/><br/>[1] Reiss, P.; Carrière, M.; Lincheneau, C.; Vaure, L.; Tamang, S., Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials. <i>Chem. Rev. </i><b>2016,</b> <i>116</i> (18), 10731-10819.<br/>[2] Kim, Y.; Lee, S., Investigating the role of zinc precursor during the synthesis of the core of III–V QDs. <i>Chem. Commun. </i><b>2022,</b> <i>58</i> (6), 875-878.<br/>[3] Janke, E. M.; Williams, N. E.; She, C.; Zherebetskyy, D.; Hudson, M. H.; Wang, L.; Gosztola, D. J.; Schaller, R. D.; Lee, B.; Sun, C.; Engel, G. S.; Talapin, D. V., Origin of Broad Emission Spectra in InP Quantum Dots: Contributions from Structural and Electronic Disorder. <i>J. Am. Chem. Soc. </i><b>2018,</b> <i>140</i> (46), 15791-15803.