Trap-Driven Exciton Recombination Processes within Femtosecond Laser-Synthesized Strongly Oxidized Silicon Nanoparticles

Trap states are central to silicon nanoparticle (Si NP) photoluminescence and charge transport properties, significantly influencing their potential for real-life applications. Laser ablation, typically conducted in a controlled environment, is an efficient technique for Si NPs synthesis that inherently minimizes the incorporation of impurities. This work presents results from time-integrated and time-resolved spectroscopic and microscopic studies of Si NPs synthesized by femtosecond laser ablation. The stationary spectroscopic and microscopic results indicate that the amorphous Si phase and oxidized SiO_x mesoporous phase cover the crystalline Si core. The analysis of time-resolved transient absorption spectra and dynamics indicates that the exciton initially photoinduced in the crystalline Si core is transferred to the shell-related trap states within approximately 2 ps. The trapped charges are further redistributed among localized states on a time scale of a few picoseconds. Finally, the traps in various Si NPs samples are depopulated into the valence band (VB) within approximately 170–190 and 1600–2100 ps. Our results highlight the importance of understanding the role of surface composition and morphology in shaping the complex photoinduced processes in the excited states of laser-synthesized Si NPs. Improving surface performance will help to increase Si NPs size-tunable photoluminescence efficiency, paving the way for developing materials suitable for future photoemitting devices.