Photophysics of single LX centers in high pressure–high temperature microdiamonds

LX centers are a recently discovered class of impurity centers in diamonds, which are characterized by nearly phononfree, spectral narrowband, and intense fluorescence at room temperature. Such a set of properties pave the way for a variety of applications, including sensing and single-photon emission. The latter requires a detailed study of photophysical processes of single emitters, which is the focus of this paper. The study of the luminescence dynamics of single LX centers in microdiamonds, synthesized by the high pressure-high temperature method, is performed by means of second-order cross-correlation function (${g}^{(2)}$) analysis. Even though the blinking is not observed directly in the measurements, the presence of photon bunching indicates that the fluorescence of a single emitter is intermittent at microsecond scale. The three-level system that is commonly used to describe intermittency of dye molecules is not consistent with the observed power dependences. We suggest a four-level energy system model with two metastable states to describe the results and perform numerical simulations to validate the model. Finally, we discuss the four-level model in the form of fluctuations of photophysical parameters.