Light-Induced Evolution of Silicon Quantum Dot Surface Chemistry—Implications for Photoluminescence, Sensing, and Reactivity

The photoluminescence of freestanding silicon quantum dots (QDs) responds rapidly to various gases in the atmosphere. Under short wavelength irradiation, the luminescence can change over a time frame of seconds to minutes and can feature orders-of-magnitude shifts in the luminescence intensity and rapid "jumps" in the peak wavelength. Starting with hydride-terminated Si QDs, the luminescence can be reversibly quenched or strongly activated, leading to a partly reversible, three-state luminescence condition consisting of regular, quenched, and activated states. These changes were characterized using photoluminescence spectroscopy, Fourier transform infrared spectroscopy, and electron spin resonance. The response is a multistep process involving several stages, including energy transfer, abstraction of hydrogen, and rapid optical-irradiation-assisted oxidation. These properties make freestanding Si QDs a potentially attractive material for optical sensor applications.