Visible emitter creation in hexagonal boron nitride by angle-dependent ion irradiation

Sagar Chowdhury, PhD

Optically active defect centers in wide-bandgap materials have gained significant research interest. Owing to their stable emission capabilities at room temperature, these color centers serve as building blocks for several quantum technologies and metrologies. While material platforms like diamond and silicon carbide (SiC) have been widely explored, hexagonal boron nitride (hBN) is a compelling alternative due to its layered architecture and ease of integration with diverse substrates and photonic systems. Due to the wide band gap, hBN hosts a diverse range of optically active defect states, with optical emission spanning the ultraviolet to near-infrared regions. However, simultaneous activation of these defect species often leads to spectral crowding and broadened photoluminescence (PL), which makes it challenging to isolate and engineer specific quantum emitters in hBN. Therefore, it is necessary to develop process strategies that enable efficient defect activation while controlling the emission spectrum. In integrated photonics, the emitters must be spectrally selective and spatially addressable for efficient light coupling.

In this talk, I will discuss our work on engineering visible-light-emitting defects in hBN using angle-dependent Xe+-ion irradiation. To achieve geometrical control over the defect activation, we systematically vary the irradiation angle, fluence, and flake thickness and identify the optimized fluence window for each condition that maximizes visible emission. Spatially resolved PL mapping, together with the ion-trajectory simulations, shows that varying the irradiation geometry reshapes the depth profile and lateral spread of the ion-induced defects, providing a direct handle to controlling emitter distributions for photonic integration. We observe a pronounced thickness-dependent shift in the optimal fluence window while overall spectral composition remains similar. The time-resolved PL also shows similar excited-state dynamics under normal and oblique incidence, indicating the emission from a related family of defect states. Post-irradiation annealing redistributes the spectral weight and forms more stable defect configurations. Our results establish angle-dependent ion irradiation as an effective controlled parameter for optically active defect engineering in hBN and other van der Waals materials.