Nanomaterial toxicity and environmental concerns inspired us to develop a scalable method for fabricating quantum dots with a positive environmental impact. Milling rice creates billions of kilograms of rice husks yearly, which are an excellent source for high-quality silica (SiO 2 ) and value-added silicon (Si) powders. Herein, we synthesize SiO 2 , porous Si, and Si quantum dots (SiQDs) from rice husks containing 20 wt % SiO 2 using a conventional chemical synthesis method and investigate the structure, optical, and optoelectrical properties. The extraction yields of SiO 2 and Si powders from rice husks are 100 and 86%, respectively. The final product, decyl-passivated SiQDs, consists of 3 nm crystalline particles that are soluble in an organic solvent. A colloidal solution of the decyl-passivated SiQDs exhibits orange− red photoluminescence at a wavelength of 680 nm, with a 21% quantum yield. This colloidal solution is used to develop a SiQD LED, resulting in orange−red electroluminescence.

Colloidal silicon quantum dots (SiQDs) may potentially minimize the environmental impact of commercial LEDs and advance next-generation light sources. Many studies have investigated the optical properties of SiQDs prepared by chemical synthesis, but the essential features of surface ligands have not fully been understood. Characterizing surface ligands should have a significant impact on optoelectronic research and ensuing applications. In this study, colloidal SiQDs were synthesized by pyrolyzing hydrogen silsesquioxane, followed by thermal hydrosilylation with 1-decene. Decyl-terminated SiQDs exhibited photoluminescence (PL) in a wavelength of 730 nm and PL quantum yields (QYs) of up to 38%. Seven decyl-terminated SiQDs with different ligand coverages were synthesized by varying the reaction time of hydrosilylation between 10 min and 9 h, and then these SiQDs were assembled into LEDs. The PL spectra, PLQYs, and performance of the SiQD LEDs were evaluated as a function of the decyl-ligand coverage. The PL properties (i.e., peak wavelength and PLQY) were insensitive to changes in decyl-ligand coverage, whereas the LED performance changed significantly. In particular, a 2-fold difference in decyl-ligand coverage exhibited a 4-fold difference in electroluminescence (EL) turn-on voltage and a 17-fold difference in EL external quantum efficiencies. In addition, the LED performance was characterized by quantifying the relationship between ligand coverage, the number of bonding sites, and the surface areas of the ligands. At greater than 25% coverage, the total surface area of the decyl-ligands was significantly larger than that of a single SiQD, and when decyl-ligands and Si–O groups covered 50% of the surface, the insulation effect impaired the LED performance. Therefore, ligand coverage significantly affected the performance of SiQD LEDs. Although this study was limited to decyl-terminated SiQDs, the same method can be applied to other ligands to further improve LED efficiency of next-generation light sources in displays, lighting, and biomedical imaging.