A convenient strategy for tunable quasi-WGM lasing in pyramid structures enabled by Förster resonance energy transfer

In this study, we present a novel implementation of three-dimensional pyramid structures as optical resonators that can generate multiple quasi-whispering gallery mode (WGM) lasing sets corresponding to varying perimeter lengths along the structure's height. Polyvinyl alcohol (PVA) polymer embedded with CdSe/ZnS quantum dots (QDs) was used as the gain medium to form pyramid structures. Through optical excitation, quasi-WGM lasing was readily observed in pyramids incorporating 640 nm CdSe/ZnS QDs. To further enhance lasing performance, Förster resonance energy transfer (FRET) is employed by incorporating 540 nm CdSe/ZnS QDs as donors to enhance the emission and increase the lasing Q factor of the 640 nm CdSe/ZnS QD acceptors. The efficiency of FRET is determined to be as high as 68%, resulting in more than a fivefold enhancement of the Q factor and a substantial reduction in the quasi-WGM lasing threshold. Moreover, the unique features of pyramid resonators help us more easily observe and control height-dependent quasi-WGM behavior, which enables precise and efficient modulation of multiple quasi-WGM sets from a single microcavity. These findings may offer a valuable alternative for applications ranging from bio-imaging to optical communication.