Bound-States-in-the-Continuum-Induced Directional Photoluminescence with Polarization Singularity in WS Monolayers.

Monolayer transition metal dichalcogenides are promising materials that not only are atomically thin but also have direct bandgaps, making them highly regarded in optics and optoelectronics. However, their photoluminescence exhibits almost random polarization at room temperature. The emission is also omnidirectional and weak due to the low quantum yield. These limitations hamper the development of practical optoelectronic devices and solid-state single-photon sources for quantum technologies. Here, we demonstrate the spatial control of photoluminescence polarization by coupling monolayer tungsten disulfide with photonic bands having bound states in the continuum. We design a dielectric photonic crystal slab with bound states in the continuum that spectrally overlap with the excitonic resonance of the monolayer of tungsten disulfide. Integration with the photonic crystal slab modulates the directionality and improves the intensity of photoluminescence through extraction and excitation enhancement. Our results will enable the development of compact on-chip optoelectronic and quantum photonic devices based on two-dimensional materials.