Silicon (Si) nanomaterials with bright luminescence in the visible region are promising materials for use as the nextgeneration light source in displays, lighting, and biomedical imaging. A scalable and cost-effective method for the synthesis of Si quantum dots (SiQDs) is essential for research and development in the field of quantum dots. Herein, we show a facile and costeffective method for controlling the structure and properties of SiQDs, obtained using the pyrolysis of hydrogen silsesquioxane (HSQ) polymer precursors synthesized using methanol. The amount of methanol added to trichlorosilane prior to the addition of water is a key factor that determines the structure and crosslinking density of the HSQ polymer used as the precursor. In turn, these features control the SiQD size, crystallinity, and luminescence efficiency. Dodecyl-passivated SiQDs of size 3−4 nm are obtained as a final product and show red photoluminescence (PL) at approximately 700−800 nm with the peak wavelength depending on the size of SiQDs. The PL quantum yield ranged from 10 to 25% with the highest value obtained for the smaller SiQDs with higher crystallinity. The present study provides new insight into the SiQD synthesis procedure and the understanding of the reaction mechanism. Furthermore, it was found that only methanol is the crucial reagent and the facile and cost-effective synthesis method can be controlled merely by changing the amount of methanol.

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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.

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Initially established catalysis mechanism for the decomposition of VOCs on noble-metal-free hydroxyapatite catalysts.

Carbon nano-onion is synthesized via microwave pyrolysis of fish scale waste in seconds. Simultaneous surface functionalization facilitates bright visible-light emission and excellent dispersibility, enabling the fabrication of flexible film and LED.