Electronic transitions of single silicon vacancy centers in the near-infrared spectral region

Photoluminescence (PL) spectra of single silicon vacancy (SiV) centers in diamond frequently feature very narrow room temperature PL lines in the near-infrared (NIR) spectral region, mostly between 820 nm and 840 nm, in addition to the well known zero-phonon line (ZPL) at approximately 738 nm [E. Neu et al., Phys. Rev. B 84, 205211 (2011)]. We here exemplarily prove for a single SiV center that this NIR PL is due to an additional purely electronic transition (ZPL). For the NIR line at 822.7 nm, we find a room temperature linewidth of 1.4 nm (2.6 meV). The line saturates at similar excitation power as the ZPL. The ZPL and NIR line exhibit identical polarization properties. Cross-correlation measurements between the ZPL and the NIR line reveal anticorrelated emission and prove that the lines originate from a single SiV center, furthermore indicating a fast switching between the transitions (0.7 ns). $g^{\left(2\right)}$ autocorrelation measurements exclude that the NIR line is a vibronic sideband or that it arises due to a transition from/to a metastable (shelving) state.

Figure 1

PL spectrum of a single SiV center. All spectra have been normalized to the ZPL. (a) Overview spectrum revealing a bright ZPL with low sideband contributions. The solid lines give Lorentzian fits to the data. The inset shows the dominant narrow PL line in the region $\lambda >800$ nm. (b) Zoomed image of the spectral region revealing the vibronic sidebands.

Figure 2

Saturation curves measured for the single SiV center. Filled squares (open circles) represent the data points; the solid line (dashed line) represents the fit using Eq. (1) for the ZPL (NIR line). The measurement for the NIR line has been corrected for the lower detection efficiency.

Figure 3

Polarization measurements for a single SiV center: (a) measurements for the 822.7 nm line; (b) measurements for the 739.1 nm ZPL. Filled squares (open circles) represent the measured data of polarized absorption (emission polarization). Solid lines (dashed lines) give the sinusoidal fits to the absorption (emission) data. To enable comparison of the data, all measurements have been normalized to one.

Figure 4

Intensity correlation measurements [normalized assuming $g^{\left(2\right)}\left(\tau \right)=1$ for long delay times $\tau$]. Note that adjacent $g^{\left(2\right)}$ functions have been shifted for clarity [(a), (c) adjacent $g^{\left(2\right)}$ functions shifted by 1; (b) adjacent $g^{\left(2\right)}$ functions shifted by 0.5]: (a) $g_{\text{ZPL}}^{\left(2\right)}$ (739.1 nm line) $0.62P_{\text{sat}}-2.92P_{\text{sat}}$, (b) $g_{\text{ZPL}}^{\left(2\right)}$ $0.08P_{\text{sat}}-0.37P_{\text{sat}}$, (c) $g_{\text{NIR}}^{\left(2\right)}$ (822.7 nm line) with increasing excitation power ($0.32P_{\text{sat}}$, $0.81P_{\text{sat}}$, $1.49P_{\text{sat}}$), and (d) intensity cross-correlation $g_{\text{cross}}^{\left(2\right)}$ of 739.1 nm and 822.7 nm line (approximately $0.3P_{\text{sat}}$) (further explanation see text). Solid lines represent fits using Eq. (5) convoluted with the instrument response function of the HBT setup.

Figure 5

Parameters $a$, ${\tau }_1$, and ${\tau }_2$ obtained for the $g^{\left(2\right)}$ measurements. Black solid lines give the intensity dependent curves for the ZPL $g^{\left(2\right)}$ function in the intensity dependent deshelving model. Gray, dashed curves are plotted using the model with constant deshelving (for explanation, see text).

Figure 6

Normalized occupation of state 3 and state 2, simulated using $k_{23}=5.8$ MHz, $k_{21}=1.16$ GHz, $k_{31}^0=0.27$ MHz, $d=18.96$ MHz, $\sigma =8.4$ MHz/$\mu$W, and $c=66.6$ $\mu$W. (a) $P=7$ $\mu$W, (b) $P=35$ $\mu$W, (c) $P=140$ $\mu$W, and (d) $P=210$ $\mu$W. The excitation powers roughly correspond to $0.1P_{\text{sat}}$, $0.5P_{\text{sat}}$, $2P_{\text{sat}}$, and $3P_{\text{sat}}$. Insets show zoomed images.

Figure 7

Schematic representation of the extended model including the NIR transition. The level scheme included in the dashed box indicates the level scheme for the intensity dependent deshelving model. Length of the NIR transition and of the ZPL transition drawn to scale.