Defect-induced multiphoton absorption and photoluminescence in BN for bio-imaging

Emerging two-dimensional materials are known for their excellent optical properties. Boron nitride (BN) is the only 2D material which exhibits multi-photon absorption. This combined with tunable defect-induced photoluminescence in BN could be used for multi-photon bio-imaging. Previously, a two-photon absorption process was proposed for explaining non-linear optical absorption in BN. However, as discussed in this talk, we show that defects (such as C and O) in BN result in mid-gap states that enable three-photon absorption in addition to tunable emission. The non-linear optical properties of BN could be used for bio-imaging at longer wavelengths which facilitate higher penetration depth and the resolution in vivo.