Exciting Hybrid Optical Modes with Fano Lineshapes in Core-Shell CsPbBr3 Microspheres for Optical Sensing

Whispering gallery modes (WGMs) supported with micrometer resonators have been widely applied in optical sensing and lasing action. In general, WGMs with high-quality factors can only be achieved in large resonators made of materials with low optical loss. Here, we report the excitation of hybrid optical modes, which originate from the interference between WGMs and high-order Mie resonances, in polystyrene microspheres and perovskite (CsPbBr3) microspheres with core-shell structures. It is found that such optical modes can be effectively excited by exploiting the evanescent wave generated on a thin metal film with s-polarized light. These optical modes exhibit wavelength-dependent Fano lineshapes characterized by asymmetric parameters with different values. We show that such optical modes excited in core-shell CsPbBr3 microspheres exhibit a strong dependence on the geometrical parameters and refractive indices of the core-shell structure. This unique feature is exploited to monitor the phase transition in the annealing process of CsPbBr3 microspheres induced by femtosecond laser pulses, which leads to significantly enhanced two-photon-induced luminescence and a blue shift of the optical modes as large as similar to 7 nm. In addition, this property is also employed to sense the water vapor in the atmosphere with a sensitivity of similar to 0.038 nm/%. Our findings indicate that the hybrid optical modes excited in core-shell CsPbBr3 microspheres, which are sensitive to heat and humidity, can be exploited to realize highly sensitive optical sensing.

Automated summary

This study reports the excitation of hybrid optical modes in polystyrene microspheres and perovskite microspheres with core-shell structures. These optical modes can be effectively excited by exploiting the evanescent wave generated on a thin metal film. The sensitivity of the optical modes to the geometrical parameters and refractive indices of the core-shell structure allows for monitoring of phase transition and sensing of water vapor.