Figure 3.

(a) EPR echo pulse sequence used in the measurement. ${\mathit{\tau }}_{\mathrm{laser}}$ is the delay time used for the lifetime decay measurement and ${\mathit{\tau }}_{\mathrm{echo}}$ is the echo time. (b–f) EPR spectra of polycrystalline samples under study obtained by experiment and simulation: (b) optically polarized EPR powder spectrum of microdiamonds with MW frequency of 11.63 GHz. (c) EPR powder spectrum of microdiamonds with MW frequency of 11.63 GHz without the laser pulse irradiation. (d) Optically polarized EPR powder spectrum of nanodiamonds with MW frequency of 11.52 GHz. (e) EPR powder spectrum of powder BA doped with 0.04 mol% pentacene with MW frequency of 11.66 GHz. (f) Simulated EPR powder spectra of thermal state triplet electron in NV ${}^{-}$ center and pentacene at 11.6 GHz. The shaded area is the magnetic field-sweep range $B_{\mathrm{sweep}}$ for each system.