(138d) Defect Engineering in Hexagonal Boron Nitride Towards Practical Quantum Applications

Single-photon emitters (SPEs) are essential building blocks in photonic quantum technologies. Hexagonal boron nitride (hBN) is emerging as a promising two-dimensional (2D) material that can host bright, room-temperature SPEs. Emitting defects in hBN exhibit a wide range of emission energies, but identifying the properties and origins of specific emitters remains challenging, which is confounded by the exponential scaling of potential candidates with the number of lattice atoms removed. To address this challenge, we collect more than 2000 spectra consisting of single, isolated zero-phonon lines in the visible range, and observe that most of them are organized into 6 discretized emission energies. We then develop facile, scalable chemical processing schemes based on water and boric acid etching that generate or interconvert specific emitters, respectively. The identification and chemical interconversion of these discretized emitters should significantly advance our understanding of the solid-state chemistry and photophysics of hBN defects. The promise of utilizing these emitting defects for practical applications can be seriously limited by commonly observed photobleaching. We present a systematic study comparing diverse hBN samples in a controlled atmospheric environment. Independent of the source or the number of layers of hBN, we find that the photobleaching of a common emission at 1.98 ± 0.05 eV can be described by two consistent time constants. Only the former is environmentally sensitive, and can be mitigated by shielding oxygen, whereas the latter is the result of carbon-assisted defect migration. We further colocalize the photobleaching experiment with scanning transmission electron microscopy, and present a rich variety of atomic-scale defect structures in hBN with unprecedented crystallographic details. Our findings reveal a key to photostable luminescence in hBN, and provide new insight into the structural origins of hBN quantum emission.