Figure 2.

Cross-relaxometry principle. (a) Cross-relaxometry offers spectral information. If T1 experiments are done in the presence of a varying magnetic field B, there is a condition where the energy difference between the NV center energy levels equals the difference in the energy levels of the spins in the sample. When the magnetic field is swept, there is a peak at this energy which is characteristic for the sample spin. (b) Example spectrum taken with the cross-relaxometry method. The scan over the Larmor frequency of 1H is shown in red. Data from ref (13).