Quantum Emitters in Hexagonal Boron Nitride Have Spectrally Tunable Quantum Efficiency

Understanding the properties of novel solid-state quantum emitters is pivotal for a variety of applications in research fields ranging from quantum optics to biology. Recently discovered defects in hexagonal boron nitride are especially interesting, as they offer much desired characteristics such as narrow emission lines and photostability. Here, the dependence of the emission on the excitation wavelength is studied. It is found that, in order to achieve bright single-photon emission with high quantum efficiency, the excitation wavelength has to be matched to the emitter. This is a strong indication that the emitters possess a complex level scheme and cannot be described by a simple two or three-level system. Using this excitation dependence of the emission, further insight to the internal level scheme is gained and it is demonstrated how to distinguish different emitters both spatially as well as in terms of their photon correlations.