Generation of luminescent defects in hBN by various irradiation methods

Hexagonal Boron Nitride (hBN) is a van der Waals (vdW) crystal with a very widebandgap and often used as insulating layer for other vdW materials, like graphene. Luminescentcentres in hBN have recently been gathering much attention because of their brightness andtheir excellent quantum properties at room temperature, which would make them competitivewith state-of-the-art quantum emitters, like the NV center in diamond.Among the most studied luminescent centres in hBN, there is the charged Boron vacancy (V^–_B),which features a very broad photoluminescence (PL) spectrum centered around 850 nm, alongwith magnetic properties which have important applications in quantum sensing schemes.In the present work, we use a Helium Ion Microscope (HIM) for irradiating hBN flakes, eitheron bare Si/SiO₂ substrate or stacked on thick Graphite flakes, to generate luminescent centres like the V^–_B. We perform in-depth PL characterization of these centres at different laserexcitation wavelengths, power and polarization, and at cryogenic temperature, for different hBNthicknesses and for varying HIM irradiation fluences. Our results show that this technique cansystematically produce high-quality luminescent emitters, in good agreement with literature,and allow us to have a good benchmark for further studies on V^–B emitters in hBN.