Phonon-Assisted Photoluminescence and Exciton Recombination in Monolayer Aluminum Nitride

Efficient solid-state photon emitters with longer operating lifetimes in the ultraviolet (UV) wavelength range are crucial for optoelectronic devices. However, finding suitable material candidates has been a significant challenge. Here, we demonstrate that hexagonal aluminum nitride (AlN) monolayers exhibit strong photoluminescence emission within the UV range of 3.94 - 4.05 eV. We show that these emissions in indirect bandgap AlN are facilitated by phonon modes with finite lattice momentum. These phonon modes promote efficient recombination of electrons and holes from the $\Gamma$ to K point of the Brillouin zone. Our findings provide a foundation for developing advanced optoelectronic devices and efficient UV light sources based on hexagonal AlN monolayers.