The $N_2V$ color center: a ubiquitous visible and near-infrared-II quantum emitter in nitrogen-doped diamond

TL;DR

This study reveals that the $N_2V$ color center in nitrogen-doped diamond emits in the visible and NIR-II range, is widespread across various diamond types, and can be used for bioimaging, opening new avenues for quantum and photonic applications.

Contribution

It demonstrates the ubiquity of the $N_2V$ center in different diamond forms and explores its optical properties and potential for bioimaging in the NIR-II spectrum.

Findings

$N_2V$ is present in various diamond types including CVD and HPHT.

The $N_2V^-$ charge state has a PL lifetime of 0.3 ns.

$N_2V$ enables stable NIR-II photoluminescence in nanodiamonds for bioimaging.

Abstract

Photoluminescent defects in diamond, like the nitrogen-vacancy (NV) color center, are at the forefront of emerging optical quantum technologies. Most emit in the visible and near-infrared spectral region below 1000 nm (NIR-I), limiting their applications in photonics, fiber communications, and biology. Here, we show that the nitrogen-vacancy-nitrogen ($N_2V$) center, which emits in the visible and near-infrared-II (NIR-II, 1000-1700 nm), is ubiquitous in as-synthesized and processed nitrogen-doped diamond from bulk samples to nanoparticles. We demonstrate that $N_2V$ is also present in commercially available state-of-the-art NV diamond sensing chips made via chemical vapor deposition (CVD). In high-pressure high-temperature (HPHT) diamonds, the photoluminescence (PL) intensity of both $N_2V$ charge states, $N_2V^0$ in the visible and $N_2V^-$ in the NIR-II, increases with increasing substitutional nitrogen concentration. We determine the PL lifetime of $N_2V^-$ to be 0.3 ns and compare a quantum optical and density functional theory model of the $N_2V^-$ with experimental PL spectra. Finally, we show that detonation nanodiamonds (DND) show stable PL in the NIR-II, which we attribute to the $N_2V$ color center, and use this NIR-II PL to image DNDs inside skin cells. Our results will contribute to the scientific and technological exploration and development of the $N_2V$ color center and inspire more research into its effect on other color centers in diamond.