Photophysical Properties of Ball Milled Silicon Nanostructures
Luminescent silicon nanocrystals (SiNCs) have attracted scientific interest for their potential use in LEDs, displays, lasers, photovoltaic spectral-shifting filters and for biomedical applications. A lot of efforts have been made to improve the radiative emission rate in SiNCs mostly using quantum confinement, strain and ligands. Existing methods, however, are not easily up-scalable, as they do not provide high material yield required for industrial applications. Besides, also photoluminescence (PL) efficiency of SiNCs emitting in the visible spectral range remains very low. Hence, there is a need to develop a low-cost method for high material yield of brightly emitting SiNCs. Theoretically, strain can be used alongside with quantum confinement to modify radiative emission rates and band-gaps. In view of that, high-energy ball milling is a method that can be used to produce large quantities of highly strained SiNCs. In this technique, balls with high kinetic energy collide with the walls of the chamber and other balls, crushing the particles in between, followed by wielding, fracture and re-wielding phenomena, reducing the particle size and increasing strains in the samples. In this study, we have used high-energy ball milling in inert gas atmosphere to synthesize SiNCs and study their photophysical properties. The induced accumulation of high strain, quantum confinement and possibly also impurities in SiNCs result in visible light spectrum PL at room temperature. This method is low cost and easily up-scalable to industrial scale.