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.
The photophysics of the nitrogen-vacancy (NV) center in diamond has been extensively investigated. Especially the fast optical switch based on the NV centers' photoluminescence (PL) by the near-infrared laser (NIR) modulation has been demonstrated, but the photophysical processes behind it are still not fully understood. Here, the NIR modulation on the PL of an isolated single NV center in bulk diamond is probed and detected with precision at picosecond timescale. We thereby observe NIR optical excitation at the NV ground state as well as at the excited state. Meanwhile, a generalized model is constructed with additional energy levels that can be reached under NIR illumination. The transition rates from numerical simulations are demonstrated in good agreement with the experimental results. Our findings may provide insights into the understanding of the NV center's related photophysics and open intriguing prospects such as reversible optical switching, super-resolution microscopy, and so forth.
A study of the photophysical properties of nitrogen-vacancy (NV) color centers in diamond nanocrystals of size 50 nm or below is carried out by means of second-order time-intensity photon correlation and cross-correlation measurements as a function of the excitation power for both pure charge states, neutral and negatively charged, as well as for the photochromic state, where the center switches between both states at any power. A dedicated three-level model implying a shelving level is developed to extract the relevant photophysical parameters coupling all three levels. Our analysis confirms the very existence of the shelving level for the neutral NV center. It is found that it plays a negligible role on the photophysics of this center, whereas it is responsible for an increasing photon bunching behavior of the negative NV center with increasing power. From the photophysical parameters, we infer a quantum efficiency for both centers, showing that it remains close to unity for the neutral center over the entire power range, whereas it drops with increasing power from near unity to approximately 0.5 for the negative center. The photophysics of the photochromic center reveals a rich phenomenology that is to a large extent dominated by that of the negative state, in agreement with the excess charge release of the negative center being much slower than the photon emission process.