  Understanding the properties of novel solid-state quantum emitters is pivotal
for a variety of applications in field 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, we study the dependence of the emission on the
excitation wavelength. We find 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, we thus gain further
insight to the internal level scheme and demonstrate how to distinguish
different emitters both spatially as well as in terms of their photon
correlations.
