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Single photon emitters play a central role in the rapidly developing field of quantum technologies. Therefor new single photon sources are highly sought after. Understanding their properties is essential for their applications in integrated quantum technologies. Defect centers in hexagonal boron nitride (hBN) have become prominent candidates as single photon sources during the last years due to their highly favorable properties, like bright emission, narrow linewidth, and high photostability at even at room-temperature. Several recent studies have shown a spectral dependency on the excitation wavelength of fluorescence behavior of these emitters1,2. In general, both the intensity and second order autocorrelation function, as well as the emission spectrum, vary with the excitation wavelength. By tuning the excitation over a broad range inside the visible spectrum and performing measurements regarding the quantum nature as well as the spectral decomposition of the emission light, we gain further insight to the characteristic properties and energy level schemes of these defect centers. Especially interesting for the energetic investigation of individual emitters is the appearance of additional sharp emission lines at higher excitation frequencies. These lines can be interpreted as higher order excited states of the same quantum system. To verify the assumption of a single system as the origin of these additional states, spectral cross correlations between individual lines are measured in a free beam HBT setup. Further analysis of these excited states can be done by performing fluorescence life time measurements, as well as comparison between the emission rates in order to determine the efficiency of the different decay channels.
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