Photoluminescent Si/SiO₂ Core/Shell Quantum Dots Prepared by High-Pressure Water Vapor Annealing for Solar Concentrators, Light-Emitting Devices, and Bioimaging

As non-toxic, elementally abundant, and low-cost luminophores, silicon quantum dots (Si QDs) suit a wide variety of applications, from luminescent devices, such as solar concentrators and light-emitting diodes, to bioimaging. Nonthermal plasma-assisted decomposition of silane gas is an efficient, relatively sustainable, and controllable method for synthesizing Si QDs. However, as-synthesized Si QDs have a high defect density and require additional passivation for utilization in these settings. Liquid-based passivation methods, such as thermal hydrosilylation, organically cap Si QDs but cannot prevent oxidation upon exposure to ambient air. Native oxidation effectively passivates the Si QDs and ensures long-term stability in air but typically requires long exposures to ambient conditions. Here, we report the use of high-pressure water vapor annealing (HWA) to quickly obtain Si/SiO₂ core/shell quantum dots with tunable photoluminescence (PL). We first show that the injection of additional hydrogen gas, commonly used in synthesizing organically capped Si QDs, is detrimental to achieving stable silica shells. Then, we demonstrate that varying the applied pressure tunes the PL quantum yield. At higher pressures, the formed silica shells are fully thermally relaxed. Lastly, we report the influence of silica shell thickness, with thicker silica shells leading to environmentally stable quantum yields of >40%. Compared to both thermal hydrosilylation and native oxidation, HWA is a convenient and rapid technique for surface passivation.