Fig. 3

a–b Simulated angle-resolved reflectance spectra under a) x-polarized beam and (b) y-polarized beam for the wavelength range 530–700 nm. The ratio between the projected in-plane momentum k_x and free-space momentum k₀ indicates the reflection angle sinθ = k_x/k₀. c–d Upconversion luminescence spectra from UCNPs deposited on the metasurface and on glass substrate under x-polarization detection (c) and y-polarization detection d. Inset: Fourier-plane upconversion photoluminescence images. (e)The linewidth of luminescence spectra of UCNPs on the metasurface and glass substrate. f The upconversion luminescence intensities from UCNPs deposited on glass and metasurface, as a function of the excitation power density for the green and red emissions, respectively. g Luminescence enhancement factors at emission wavelengths of 540 nm (green) and 660 nm (red) as a function of the 980 nm incident excitation power. h Emission lifetime measurements at 540 nm for UCNPs deposited on resonant metasurface supporting Mie resonant mode (green) and on a glass slide (black) under x-polarization detection. i Time-resolved photoluminescence measurements of UCNPs deposited on a glass slide (black) and a metasurface supporting quasi-BIC mode (red) at an emission wavelength of 660 nm under y-polarization detection