Various optical phenomena can be induced in periodic arrays of nanoparticles by the radiative coupling of the local dipoles in each particle. Probably the most impressive example is bound states in the continuum (BICs), which are electromagnetic modes with a dispersion inside the light cone but infinite lifetime, that is, modes that cannot leak to the continuum. Symmetry‐protected BICs appear at highly symmetric points in the dispersion of periodic systems. Although the addition of nonequivalent lattice points in a unit cell is an easy and straightforward way of tuning the symmetry, BICs in such particle lattice, that is, non‐Bravais lattice, are less explored among periodic systems. Starting from a periodic square lattice of Si nanodisks, three non‐Bravais lattices are prepared by detuning size and position of the second disk in the unit cell. Diffraction‐induced coupling excites magnetic/electric dipoles in each nanodisk, producing two surface lattice resonances at the Γ point with a band gap in between. The high/low energy branch becomes a BIC for the size/position‐detuned array, respectively, while both branches are bright (or leaky) when both size and position are detuned simultaneously. The unexplored role of the interplay between magnetic and electric dipoles in dielectric nanoparticles in connection with the change of BIC to bright character in the detuned arrays is discussed with the aid of a coupled electric and magnetic dipole model. This study gives a simple way of tuning BICs at telecom wavelengths in non‐Bravais lattices, including both plasmonic and dielectric systems, thus scalable to a wide range of frequencies.

The resonant phenomena of metasurfaces highly depend on the scattering strength of each component and their interferences. The losses modify the phase and reduce the amplitude of all multipoles; thus, the loss control is vital for obtaining the designed properties. Amorphous (a‐)Si has a higher absorption coefficient than that of the crystalline form, which limits its optical application. A simple rapid thermal annealing (RTA) path to refine the a‐Si metasurfaces is found. It is applied to the sputtering‐made a‐Si metasurface comprising square array of nanodisks. While the large loss smears out the resonances for the as‐made metasurface, the sharp and near‐zero reflectance with near‐perfect absorptance is achieved after RTA, satisfying the lattice Kerker condition via the interference of magnetic and electric dipoles. At the lattice Kerker condition, the forward‐enhanced and backward‐reduced directional photoluminescence is observed from the emitter layer deposited on the metasurface. The numerical results are all found to be in good agreement with the experimental results, and the multipole expansion analysis for the single nanodisk gives the physical background of this observation. This refinement of a‐Si metasurfaces by RTA treatment paves the simple and robust way for realizing thrilling optical and optoelectrical applications, such as detectors and filters.

Various optical phenomena can be induced in periodic arrays of nanoparticles by the radiative coupling of the local dipoles in each particle. Probably the most impressive example is bound states in the continuum (BICs), which are electromagnetic modes with a dispersion inside the light cone but infinite lifetime, i.e., modes that cannot leak to the continuum. Symmetry-protected BICs appear at highly symmetric