Fig. 3

Modal loss and confinement factor of guided modes. a, c Modal loss and b, d confinement factor of the guided plasmonic gap modes at fixed SiO₂ gap thickness, t_g = 0 (blue lines), 5 (red lines), and 15 (green lines) nm, corresponding to the doped perovskite in the photoluminescent spectrum from λ = 425 to 800 nm. The hybrid perovskite MAPb(Br_xCl_1-x)₃ WGs on Ag (solid lines) and Al plates (dash dotted lines) are calculated as shown in (a, b). Those of perovskite MAPb(I_yBr_1-y)₃ WGs on Ag (solid lines), Al (dash dotted lines) and Au (dash lines) plates are solved at λ = 555 to 800 nm as shown in (c, d). The insets in (b, d) reveal the modal profiles |E| of the guided plasmonic gap modes on SiO₂-covered Ag plates of t_g = 5 nm for the doped perovskites of compositions x = 0 (yellow circle), x = 0.58 (red circle), y = 0 (orange circle), and y = 0.59 (green circle)