Spectroscopy of photoionization from the $^1E$ singlet state in nitrogen$-$vacancy centers in diamond

TL;DR

This study measures the energy levels of the singlet states in nitrogen-vacancy centers in diamond, crucial for quantum technologies, using photoluminescence spectroscopy under various conditions.

Contribution

It provides the first direct measurements of the energy gap between the singlet and triplet states in NV centers, revealing their position within the diamond bandgap.

Findings

Identified the energy gap between singlet and triplet states.

Observed ionization effects under magnetic fields.

Located singlet states within the diamond bandgap.

Abstract

The $^1E-^1A_1$ singlet manifold of the negatively charged nitrogen vacancy $(NV^-)$ center in diamond plays a central role in the quantum information and quantum sensing applications of the $NV^-$ center. However, the energy of this manifold within the diamond bandgap and with respect to the $^3A_2-^3E$ triplet manifold has not been measured directly. Using field-quenching effects on photoluminescence (PL) spectra, we report on the energy gap between the $^1E-^1A_1$ singlet manifold and the $^3A_2$ and $^3E$ ground and excited triplet states of the $NV^-$ as a function of excitation wavelength and power, temperature, and applied magnetic field in a heavily nitrogen-doped sample. Increased PL and decreased zero-phonon line width from the $NV^0$ were observed in the presence of an applied magnetic field, indicating ionization from the long-lived $^1E$ singlet state. A temperature-dependent ionization threshold between 532 nm and 550 nm was found, locating the singlet states within the diamond band gap.