Fig. 1. (a) Schematic diagram of the plasmon-assisted mode selection lanthanide-based microcavity. (b) Transmission electron microscope image of (i) NaYF4:20%Yb3+/2%Tm3+ UCNPs, (ii) scanning electron microscope (SEM) image of SiO2@UCNP microsphere, (iii) atomic force microscope image of the silver microplate and its corresponding height profile, and (iv) SEM image of SiO2@UCNP microsphere on the silver microplate. (c) Simplified energy-level diagram describing the plasmon-assisted selective enhancement process of the TE mode. (d) Fluorescence emission spectra of UCNPs and a SiO2@UCNP microsphere.

Fig. 2. (a) Pumping power-dependent plots of emission intensities and spectral linewidth narrowing of 802-nm lasing on the glass substrate exhibiting upconversion lasing emissions. (b) Polarization investigation of the 788- and 802-nm lasing lines using a polar plot of the intensities; the fitting curves were drawn by a cosine-square function.

Fig. 3. (a) Fluorescence emission spectra of SiO2@UCNP microsphere on the glass substrate and silver microplate. (b) Emission polarization spectra of SiO2@UCNP microsphere on the glass substrate and silver microplate when the polarizer was at 90 deg. (c) COMSOL-simulated emission spectra corresponding to panel (a). (d) Charge distribution diagram of the silver microplate excited by (i) Ex, (ii) Ey, and (iii) Ez dipole on the microsphere.

Fig. 4. (a) Enlarged view of the lasing mode peak near 798 nm on the silver microplate. (b) Fluorescence spectrum of the corresponding lasing peak in panel (a) when the polarizer in the collected optical path was at 0 and 90 deg.

Fig. 5. (a) Bright-field microscopy image of a microlaser remotely excited by SPPs. The red and blue circles represent the excitation and collection positions, respectively. The angle θ in the lower right corner represents the polarization angle of the excited light. (b) Microcavity on the silver microplate at the excitation point corresponds to different emission spectra with the change in polarization angle of excitation light.