Functional Silicon Nanoparticles with Sizes Ranging from Single Nanometers to Sub-Micrometers

Si forms not only the backbone of microelectronics technology but also gains in significance for photonics when its size is down to nanoscale. Depending on its size (1-1000 nm), Si nanostructures exhibit different optical responses. In this presentation, we show the optical properties of Si nanoparticles with two different size regimes. For sub-10 nm in size, so-called quantum dots (QDs), the quantum confinement effect enables the efficient photoluminescence (PL) and facilitate the applications as light emitters. The properties can be also controlled by doping impurities. Here we present a comprehensive study on colloidal Si QDs codoped with boron (B) and phosphorus (P).[1,2] We show the detailed structural and optical characterization and demonstrate that the codopants modify the electronic structures of Si QDs and introduce donor and acceptor levels in the band gap of Si QDs. This enables the optical transition with the energy below bulk Si bandgap (~1.1 eV). We will demonstrate the potential applications of codoped Si QDs in photonics and biomedical fields.<br/>The second part of the presentation focuses on Si nanoparticles with 100-250 nm in diameter that exhibit electric and magnetic Mie resonance in the visible to near-IR range due to the high refractive index of Si, which can be utilized as optically resonant antennas. We develop monodispersed Si nanoparticles in solution and show the structural colors by size-dependent Mie resonances. We also discuss optical functionalities and Mie-resonance-enhanced light matter interactions in different materials such as emitting lanthanoid ions and two-dimensional materials.<br/>[1] Nano Lett., 16, 2615 (2016). [2] Nano Lett., 18, 7282 (2018). [3] Adv. Opt. Mater., 8, 2000033 (2020). [4] Nano Letters, 20, 7737 (2020). [5] ACS Photon., 8, 1794 (2021). [6] ACS Photon., 9, 1741 (2022).