Enhanced lasing from organic gain medium by Au nanocube@SiO₂ core-shell nanoparticles with optimal size

We report a dramatic enhancement of random lasing assisted by Au nanocubesilica core-shell nanoparticles (Au NC@SiO₂ NPs) with optimal size. To determine which size of Au NC@SiO₂ NPs would have the optimal plasmon effect, we first investigated the lasing properties based on different sizes of bare Au nanocubes (Au NCs) with different localized surface plasmon resonance (LSPR) spectra; the edge lengths of the Au NCs ranged from 20 nm to 120 nm. The 80 nm Au NCs, whose LSPR spectrum had the largest overlap with the emission spectrum of the gain medium, exhibited the strongest scattering and electric field intensity to better enhance the lasing. Compared to the gain media with bare Au nanocubes or Au nanosphere@SiO₂ nanoparticles, the gain medium with optimally sized Au nanocube @SiO₂ NPs had the lowest lasing threshold, only 21.7% of that of the neat gain medium. This was attributed to the stronger scattering and electric field enhancement localized at the spiky tips of the Au NCs, and the fact that the SiO₂ shell reduced the absorption loss of the dyes in close proximity to the Au NCs. Using the proper size of Au NC@SiO₂ NPs provides an ideal way to achieve low-threshold plasmon random lasing by tuning the LSPR of metallic nanostructures.