Stability of Silicon Quantum Dots Against Solar Light/Hot Water: RGB Foldable Films and Ligand Engineering

Abstract

Heavy-metal-free fluorophores such as silicon quantum dots (SiQDs) are required for next-generation light sources to address environmental concerns. However, few studies on SiQD devices are concerned with flexible devices, luminescence colors other than red, or stability data. Herein, the synthesis via three different methods of colloidal SiQDs exhibiting red/green/blue (RGB) photoluminescence (PL) is presented. The durability of each RGB SiQD embedded in a flexible polymer film (>4 × 4 cm 2 ) and exposed to solar light or hot water is evaluated. The nature of the terminating ligand on the SiQD surface significantly affects PL stability. In particular, SiQDs passivated with siloxane groups exhibiting blue PL retained 80% of their initial PL intensity after solarlight exposure for 8 days. These blue SiQDs embedded in a film retain 94% of their original PL quantum yield (PLQY) after 12 days at 80 °C in water. The types of ligand, coverage, and host material properties (light absorptivity, permeability, and hydrophobicity) are critical for enhancing the PLQY, radiative rate, and durability of SiQDs. These new insights are invaluable for designing heavy-metal-free light sources, accelerating their use, implementing them, and integrating them into curved substrates with soft textures and improved flexibility and stretchability, leading to foldable optoelectronics, e-skins, and wearable devices.

Formation of Blue-Emitting Colloidal Si Quantum Dots through Pulsed Discharge of Si Strips in Distilled Water Medium

“…The corresponding PLQY is 5.1%. Previous research on Si QDs has revealed the influence of size distribution 12−14 and surface properties 15,72,73 on their optical properties. Fujimoto et al 72 The above results suggest the delicate control of discharge conditions and the size of the Si strip are conducive to from Si QDs through PWD.…”

“…Previous research on Si QDs has revealed the influence of size distribution 12−14 and surface properties 15,72,73 on their optical properties. Fujimoto et al 72 The above results suggest the delicate control of discharge conditions and the size of the Si strip are conducive to from Si QDs through PWD. At the charging voltage of 7.0−8.0 kV, the Si strip completely melts and evaporates to form gas Si, which expands rapidly before the formation of plasma channel.…”

“…Previous research on Si QDs has revealed the influence of size distribution − and surface properties ,, on their optical properties. Fujimoto et al investigated the blue-Si QDs passivated by the O atoms of a siloxane group (Si–O–Si). The corresponding PL mechanism is the ligand effects via recombination in the ligand-induced states instead of the quantum confinement effect based on the F (fast) band region in PL results.…”

“…The corresponding PLQY is 5.1%. Previous research on Si QDs has revealed the influence of size distribution − and surface properties ,, on their optical properties. Fujimoto et al investigated the blue-Si QDs passivated by the O atoms of a siloxane group (Si–O–Si).…”

Silicon quantum dots: surface matter, what next?

“…Among these emission characteristics is that the PL-decay (t PL ) is so fast, on the order of nanoseconds instead of micro -to milliseconds as typical alkyl-SiQD. 13,14 Fujimoto et al (2022) 15 elaborated on the difference between the F-band and S-band. The authors synthesized three types of SiQDs based on their emission.…”