Effective Cooling Generates Efficient Emission: Blue, Green, and Red Light-Emitting Si Nanocrystals

Nanosecond pulsed laser ablation of bulk silicon crystal upon the excitation of 532 run was conducted in supercritical CO2 to generate silicon nanocrystals, whose properties were studied by seven experimental methods. According to the photoluminescence spectra and fluorescence microscope images, emissions of near-ultraviolet, violet, blue, green, and red were observed in air, at room temperature, and without cooling in liquid nitrogen or a helium cryogenic system. A preferable emission channel of carriers, generated by photoexcitation Of Si/SiO2 of core/shell structure, was responsible for interface states with defect sites. This luminescence process caused color changes and intensity increase, enhanced by a factor of 100, where thermal properties of supercritical CO2 were maximized, due to critical anomaly. It was found that colors and intensities of photoluminescence of silicon nanocrystals are controlled by a cooling rate during ablation, whose quantity is Manipulated by the supercritical fluid pressure.