Optimizing the excitation wavelength of boron vacancy defects in hexagonal boron nitride.

Boron vacancy defects (V_B^-) in hexagonal boron nitride (hBN) are promising sensors for magnetic fields, temperature, and pressure. Unlike nitrogen vacancy (NV) centers, V_B^- defects are active just an atomic layer below the material surface. The sensor/sample standoff distance achievable with V_B^- defects could enable significant benefits for standoff-critical applications such as nanoscale nuclear magnetic resonance. In addition, the ability to embed a sensor in nanometer-scale flakes could enable new applications for temperature and pressure sensing, allow integration of sensors into 2D heterostructures, and facilitate the study of properties of van der Waals materials. However, V_B^- magnetic sensitivity is inferior to that of NVs in most situations. One strategy to improve sensitivity is to optimize the laser wavelength used for optical pumping. While photoluminescence excitation measurements show maximal emission under 477 nm excitation, it is not known if this holds at typical experimental optical intensities, and most published research on V_B^- utilizes 532 nm excitation. We report progress in a study of the impact of 405, 473, 515, and 532 nm excitation on the photoluminescence, contrast, and other properties of V_B^- defects across a range of optical intensities.