Highly Luminescent Alkyl- and Alkoxy-Terminated Silicon Quantum Dots via Aging Following Single-Step Plasma Synthesis and Functionalization

Abstract

Nonthermal plasma synthesis enables the continuous production and immediate surface functionalization of silicon quantum dots (Si QDs) in a single, flow-through reactor. While this process occurs on a millisecond time scale, the resulting nanocrystals are often limited by low photoluminescence quantum yields (PLQY) due to persistent surface defects. In this work, we demonstrate that a minimal post-treatment, aging the Si QDs in specific solvents, can enhance the PLQY to ∼50%, approaching the performance of much more complex solution-phase methods. We find that the choice of the surface ligand and solvent is critical: hexanol-terminated Si QDs exhibit significantly higher initial and final PLQYs than decene-terminated particles, likely due to the faster reaction of alcohols with electrophilic surface sites in the gas phase. Among the solvents investigated, chloroform consistently yields the highest PLQY. Furthermore, we show that light irradiation at 400 and 633 nm drastically accelerates the Si QD aging process, reducing the aging time from hundreds of hours to under 20 h. This practical “synthesize and forget” strategy offers an efficient pathway for optimizing high-PLQY Si QDs for applications in optoelectronics and bioimaging.