The Effect of pH on the Photoluminescent Properties of Silicon Nanoparticles

Since the discovery of photoluminescent (PL) emissions from nanosilicon in 1990, there has been an increased effort to understand this phenomenon, as well as applications it might serve. In particular, the potential use of silicon nanoparticles (SiNPs) in the biomedical industry as optical contrast agents has garnered attention due to the non-toxicity of silicon, as well as its abundance and low cost. It is therefore prudent to understand factors that effect the PL behavior of these SiNPs in biological media. In this research, hydrogen terminated SiNPs (H-SiNPs) were synthesized using a sol-gel method, suspended in ethanol, then titrated with aqueous acid and base. The resulting behavior was then characterized with Fourier-transform infrared and photoluminescence emission and excitation spectroscopies. It was observed that suspension of red emitting H-SiNPs in ethanol led to a quenching of PL emissions and a reduction of hydrogen termination on their surface. Titration of the ethanol suspension with acid led to a resurgence of the red emissions, while titration with base did not induce any observable PL emissions. Additional modification by warming and resuspension into hexane also led to a brief resurgence of the red emissions in both cases. While the work presented here is relatively focused in scope, it raises a number of questions regarding the structure and behavior of SiNPs for future exploration and research