(color online) (a) PL spectra of gold and copper film at room temperature.^[1] (b) The band structure of gold near X and L close to the Fermi surface.^[6] (c) The enhanced PL spectra from rough copper film (dashed lines) as compared to that of the smooth sample (solid lines).^[2] (d)–(f) QYs of PL from gold nanoparticles are strongly dependent on the overlap between the excitation wavelengths and LSPR positions.^[31] (g)–(j) Gap-plasmon enhanced PL (457 nm excitation) from a Ag nanowire on a single Au nanobeam with a 6 nm-thick Al₂O₃ insulator layer.^[32] (k) Excitation wavelength dependent gap-plasmon enhanced PL from gold nanospheres on a gold film with a 3.4 nm-thick Al₂O₃ insulator layer.^[33]