The negatively charged nitrogen vacancy ($\mathrm{N}{\mathrm{V}}^{-}$) defect in diamond serves as a popular platform for manipulating and exploiting long-lived coherent spin dynamics at room temperature combined with optical readout. The required spin polarization of the spin triplet ${}^{3}A_2$ electronic ground state occurs through a cycle of repetitious optical photoexcitation events to the ${}^{3}E$ electronic excited state that is accompanied by a series of electronic transitions to a ${}^{1}A_1$ and a ${}^{1}E$ electronic state, and back to the ${}^{3}A_2$ state. The timescales of these transitions are largely known, yet for the relaxation time of the ${}^{1}A_1\to {}^{1}E$ infrared transition, which predominantly occurs via nonradiative recombination, only an upper limit of 1 ns could be determined so far. Here, we employ ultrafast transient absorption spectroscopy to probe the dynamics of the nonradiative relaxation from the ${}^{1}A_1$ to the ${}^{1}E$ state after photoexcitation of the ${}^{3}E$ state and find a relaxation time of 100 ps at a temperature of 78 K.

• Received 31 July 2018

DOI:https://doi.org/10.1103/PhysRevB.98.094309