Optical properties of the nitrogen-vacancy singlet levels in diamond

We report measurements of the optical properties of the 1042 nm transition of negatively charged nitrogen-vacancy (NV) centers in type-1b diamond. The results indicate that the upper level of this transition couples to the $m_s=\pm 1$ sublevels of the ${}^{3}E$ excited state and is short lived with a lifetime of $\lesssim 1\text{ns}$. The lower level is shown to have a temperature-dependent lifetime of 462(10) ns at 4.4 K and 219(3) ns at 295 K. The light-polarization dependence of 1042 nm absorption confirms that the transition is between orbitals of $A_1$ and $E$ character. The results shed light on the NV level structure and optical pumping mechanism.

Figure 1

(Color online) Level diagram for NV center showing spin-triplet ground and excited states, as well as the singlet system involved in intersystem crossing. Radiative transitions are indicated by solid arrows and nonradiative transitions by dashed arrows. The tentative label of the upper (lower) singlet as ${}^{1}E\left({{}^{1}A}_1\right)$ is based on the observed spin-selective decay paths (see text).

Figure 2

(Color online) (a) Apparatus used for magnetic resonance and optical studies. MC—monochromator. (b) Fluorescence spectrum of the IR transition (excitation at 532 nm) at room temperature for two diamonds with different ${\text{NV}}^{-}$ concentrations (Ref. 16) showing a ZPL at 1042.5(3) nm. The sloped background is due to the tail of the phonon sideband of the much stronger ${}^{3}E\to {{}^{3}A}_2$ transition (Ref. 26). (c) Magnetic-resonance spectra of sample S2 for visible (650–800 nm bandpass filter) and IR (1000 nm longpass filter) emission at room temperature under an applied field of $\sim 4\text{mT}$. Excitation was with $\sim 1\text{W}$ of 532 nm light, polarized in the plane of the sample surface. The variation in peak heights can be explained by the pump light and microwave polarization selection rules (Ref. 30).

Figure 3

(Color online) (a) The phase-shift technique. (b) Phase shift of visible (650–800 nm) and IR (1035–1045 nm) fluorescence as a function of modulation frequency and fits (see text). (c) Lifetime of the MS as a function of temperature as well as fits to Eq. (1). The values of $ϵ$ and ${ϵ}_{1,2}$ are the fitted phonon energies for $N=1$ and $N=2$ decays, respectively. Error bars represent the standard deviation of multiple measurements.

Figure 4

(Color online) (a) Example magnetic-resonance spectrum for visible fluorescence and transmission of IR probe at 70 K. As the sample was [111] oriented, one of the NV axes was normal to the sample surface. (b) Polar plot of the contrast of visible fluorescence (left) and IR absorption (right) as a function of light-polarization angle for both geometries (see text). Solid lines are fits to a constant and dashed lines are fits to ${\text{sin}}^2\left(\theta -{\varphi }_{\text{NV}}\right)+c$, where $\theta$ is the polarizer angle, ${\varphi }_{\text{NV}}$ is the angle of $\mathbf{z}$ relative to the polarizer axis, and $c$ is an offset which takes into account imperfections in light polarization, beam alignment, and selection rules. For the $\mathbf{z}\perp \widehat{\mathbf{k}}$ geometry, the sample and polarizer were positioned such that we expected ${\varphi }_{\text{NV}}=90\left(3\right)°$ and both of the fitted values of ${\varphi }_{\text{NV}}$ agree with this value to within the uncertainty. (c) Light-polarization axes for allowed transitions between the singlet levels (Ref. 39). The selection rules are identical for both absorption and emission.