Measuring the Singlet Lifetime of the Boron Vacancy Center in Hexagonal Boron Nitride
Richard Escalante
University of Maryland, College Park, Maryland, USA _______________________________________
Optically active defects in two-dimensional (2D) materials provide a promising platform for applications in quantum sensing. One advantage compared to defects in other wide band gap materials, such as diamond, is the potential to reduce the stand-off distance to the sensing target, thereby providing enhanced sensitivity. A recently discovered defect in a 2D material is the negatively charged boron vacancy center (VB–) in hexagonal boron nitride (hBN). It has garnered attention because of its similar electronic structure to the nitrogen vacancy (NV) center in diamond. Due to its recent discovery, many of the VB– electronic transition rates and branching ratios are not fully known. In this study, we use time-resolved measurements and < 2 ns rise time lasers, to directly measure the lifetime of the singlet state of VB– in neutron-irradiated nanoflakes of hBN. We perform this measurement on 16 different nanoflakes and obtain an average lifetime of 15.7 ± 2.8 ns. Additionally, we optically probe thermal and polarized spin distributions at several laser powers and fit the time-resolved data to a 7-level rate equation model. We place constraints on the intersystem crossing branching ratio using the measured singlet lifetime, allowing us to extract several rates in the model. Next, we report on the variability of the lower bound of the population that is polarized to the singlet state. Lastly, we discuss observations of possible ionization to the neutral charge state VB0 in large neutron-irradiated flakes of hBN. These results provide valuable insights and clarification of the rates and lifetimes governing VB– photodynamics; and contribute to optimization of VB– creation methods for use in quantum sensing.
Email: rescala1@umd.edu