Fig. 1
From: Dual-band polarized upconversion photoluminescence enhanced by resonant dielectric metasurfaces
Polarization-controlled upconversion emission enhancement. a Schematic presentation of a resonant metasurface with high-Q quasi-BIC and Mie resonant modes. The metasurface is composed of an array of TiO2 nanobricks loaded with UCNPs. b Diagram of the designed unit cell depicting dual TiO2 nanobricks with a tilt angle of δ = ±10° relative to the y-axis, placed on a SiO2 substrate. Geometrical parameters: wx=100 nm, wy = 240 nm, h = 450 nm. The rectangular lattices periods are px = 430 nm and py = 345 nm. c TEM image of NaYF4:Yb/Er upconversion nanoparticles. d Energy level diagram illustrating the upconversion transition of Yb3+/Er3+. e x- and y-polarization controlled reflection spectra of the resonant metasurfaces overlapping with the emission spectra of the NaYF4:Yb/Er upconversion nanoparticles. Yellow curves denote Mie resonance under x-polarization and magenta curves denote quasi-BIC resonance under y-polarization incidence