Charge state dynamics of the nitrogen vacancy center in diamond under 1064-nm laser excitation

The photophysics and charge state dynamics of the nitrogen vacancy (NV) center in diamond has been extensively investigated, but is still not fully understood. In contrast to previous work, we find that ${\mathrm{NV}}^0$ converts to ${\mathrm{NV}}^{-}$ under excitation with low power near-infrared (1064-nm) light, resulting in increased photoluminescence from the ${\mathrm{NV}}^{-}$ state. We used a combination of spectral and time-resolved photoluminescence experiments and rate-equation modeling to conclude that ${\mathrm{NV}}^0$ converts to ${\mathrm{NV}}^{-}$ via absorption of 1064-nm photons from the valence band of diamond. We report fast quenching and recovery of the photoluminescence from both charge states of the NV center under low power 1064-nm laser excitation, which has not been previously observed. We also find, using optically detected magnetic resonance experiments, that the charge transfer process mediated by the 1064-nm laser is spin dependent.

Figure 1

(a) Experimental confocal microscope integrated with 1064-nm cw laser. 532-nm laser, PL from NV centers and 1064-nm laser are separated by two dichroic beam splitters (DBS1 and DBS2). A moving lens (ML) in the 1064-nm laser path helps to correct the chromatic aberration of the high NA objective (Obj). Scanning mirror (SCM) helps to obtain a 2D PL image. Samples are indium soldered on the cold finger made of copper (Cu) and microwaves are delivered with an antenna (MW) to the sample. Notch 532 nm (NF) and different longpass (LP) and shortpass (SP) filters are applied for different collection windows (650 nm LP and 800 nm SP for ${\mathrm{NV}}^{-}$ or 582/75 nm bandpass filter for ${\mathrm{NV}}^0$). The PL was coupled into a single mode fiber (SM fiber) and received by a single photon counting module (SPCM) or a spectrometer (SPEC). (b) Optical image of indium soldered bulk diamond on a copper plate (yellow), the indium solder (silver) can been seen through the bulk diamond, which is $3.5\times 3.5$ mm for its dimension. (c) SEM image of 100 nm commercial nanodiamond deposited on a silicon chip.

Figure 2

(a) Photochromism behavior of NV centers in bulk diamond at room temperature 295 K under 1064-nm laser illumination (120 s exposure). ZPL of ${\mathrm{NV}}^0$ and ${\mathrm{NV}}^{-}$ are observed at 575 and 638 nm; strong Raman peak is observed at 572.8 nm. (b) Photochromism behavior of NV centers in 100 nm diamond nanocrystal at 16 K under 1064-nm laser illumination (30 s exposure). ZPL of ${\mathrm{NV}}^0$ and ${\mathrm{NV}}^{-}$ are observed at 575 and 637 nm; no obvious Raman peak is observed at 572.8 nm. Shaded ranges indicate a ${\mathrm{NV}}^0$ (yellow) and ${\mathrm{NV}}^{-}$ (red) PL collection window, shared with (a) and (b).

Figure 3

Confocal images of ensemble of NV centers in bulk diamond sample at room temperature under 0.25 mW Green excitation. (a) ${\mathrm{NV}}^{-}$ PL data. (b) ${\mathrm{NV}}^0$ PL data. (c) Time trace of the ${\mathrm{NV}}^{-}$ PL counts, under IR gating (10 mW), normalized to when IR is off. (d) Time trace of the ${\mathrm{NV}}^0$ PL counts, under IR gating (10 mW), normalized to when IR is off.

Figure 4

(a) PL versus time (Savitzky-Golay filter applied [14]) while fast switching on and off the 1064-nm laser applied by AOMs. Inner figure: Zoom in of the “slow effect.” (b) Optical pulsed sequence used in the experiments for result (a).

Figure 5

Theoretical model for NV charge state flipping. Left: Our postulated model that ${\mathrm{NV}}^0$ is excited first by the 532-nm laser (green arrow), then it captures an electron promoted by the 1064-nm laser from the valence band (pink arrow). This two-step procedure converts ${\mathrm{NV}}^0$ to ${\mathrm{NV}}^{-}$. Right: Accepted photoionization two-step procedure induced by a 532-nm laser (green arrows indicate the two steps), which converts ${\mathrm{NV}}^{-}$ to ${\mathrm{NV}}^0$ [3] through the conduction band.

Figure 6

Dependence of the charge flipping rate $r=r^{-/0}+r^{0/-}$ on the 1064-nm laser power. Green laser excitation is fixed at 0.3 mW.

Figure 7

(a) PL versus time (Savitzky-Golay filter applied [14]) under fast modulation to examine the rapid quenching behavior. Inner figure: Zoom in of the fast edges of PL counts. (b) Optical pulse sequence used for the results in (a).

Figure 8

ODMR signals comparison with IR and no IR for (a) ${\mathrm{NV}}^{-}$ charge state and (b) ${\mathrm{NV}}^0$ charge state.

Figure 9

(a) Spin dependence of ${\mathrm{NV}}^0$ PL counts (Savitzky-Golay filter applied [14], normalized to steady state) through charge state flipping after switching on the 1064-nm laser. (i) Zoom in of PL contrast. (ii) Exponentially fit of the PL contrast decay time. (b) Corresponding pulsed sequence: start with green laser initialization pulse for 2300 ns, followed with a 2.87 GHz $\pi$ pulse to flip the spin after green was off. A detection green pulse was applied 100 ns after the $\pi$ pulse and IR gating pulse was 50 ns after that.