Photoluminescence from an emitter layer sandwiched between the stack of metasurfaces

The combination of metasurface with optical emitters provides a unique opportunity to control the emission. The metasurface effect strongly depends on the spectral overlap between the internal electronic transitions of the emitter and the optical resonances of the metasurface. Elaborate design of the metasurface could realize the resonances at both absorption and emission wavelengths of the emitter, but it usually leads to complexity in fabrication. In this work, we propose a very simple strategy to obtain the resonances at both wavelengths by sandwiching the emitter layer with a pair of metasurfaces designed for absorption and emission, respectively. For this purpose, we use a sticker of Al metasurface, which is the array of Al nanoparticles embedded in a flexible polymer film that can be stuck on any clean surfaces. The metasurface stack is prepared by simply placing the sticker, resonating at the emission wavelength, on the emitter layer deposited on the $TiO2$ metasurface resonating at the absorption wavelength. The overall enhancement achieved for the stack of the metasurfaces can be understood roughly as the multiplication of contributions from the respective metasurfaces. Employing a sticker provides an easy-to-make way of constructing a stack of metasurfaces, which increases the degree of freedom in designing the metasurface-coupled emitters.