Plasmonically induced coherent and polarized random laser emissions in colloidal CdSe/ZnS quantum dots with ellipsoidal Ag nanoparticles

We demonstrate the capability of controlling the optical anisotropy of lasing emissions by manipulating the coupling between the oscillated electric field and the localized surface plasmon (LSP) resonance for a random lasing medium composed of colloidal CdSe/ZnS quantum dots (QDs) and ellipsoidal silver nanoparticles (Ag NPs). Distinctive from the amplified spontaneous emission (ASE) generally observed on the CdSe/ZnS QDs, it has been found that lasing emissions of the revealed system exhibit clear interference features with low-threshold characteristics, mainly attributed to enhanced light scatterings and optical gains arisen in the peripheral surfaces of ellipsoidal Ag NPs. Importantly, the relative orientation, between the oscillated electric field of emitted light from CdSe/ZnS QDs and the ellipse axis of Ag NPs, plays a critical role in selective excitation of LSP resonances leading to the laser emissions with preferential optical polarizations. That is further examined and validated by the finite-difference time-domain simulation. The achievement of spatial and spectral coupling of LSP resonance with colloidal QDs respectively make the present system one of the promising candidates of colloidal QDs-based random lasers to achieve coherent and polarized lasing emissions.