Fig. 1. (a) Schematic of MIM (Ag–PMMA + LDS 798 dye–Ag) cavity. (b) Simulated reflection result for different thicknesses of dielectric layer. White dashed lines show resonance position of both cavities with thicknesses of 140 nm and 190 nm.

Fig. 2. Measured reflectance spectra of (a) MIM-I and (b) MIM-II cavities. The absorption and emission spectra of LDS 798 dye molecules are presented as black and red curves in both panels, respectively. The reflectance band of MIM-I cavity overlaps with the absorption peak and the emission tail of fluorescent dye, while the reflectance band of MIM-II overlaps with the emission of the dye and barely with absorption of dye.

Fig. 3. Experimentally recorded steady-state PL spectra of LDS 798 dye molecules embedded in cavities (red solid lines): (a) MIM-I cavity and (b) MIM-II cavity. The recorded emission of embedded dye molecules in PMMA as a reference sample is shown as a black dotted line. Time-resolved fluorescence spectroscopy results of embedded dye molecules in the MIM cavities (red triangles): (c) MIM-I and (d) MIM-II. The recorded fluorescent lifetime of embedded dye in PMMA as a reference sample is shown as a black dotted line.

Fig. 4. Simulation results for the electric field contour plot in the two nanocavities: (a) MIM-I and (b) MIM-II. The insets in panels (a) and (b) show the schematics of the MIM-I and MIM-II designs, respectively. The Purcell factor calculation for the two cavities: (c) MIM-I and (d) MIM-II. The higher mode profile describes the lower Purcell factor of the MIM-II cavity with respect to that of MIM-I.