How to Identify, Attribute, and Quantify Triplet Defects in Ensembles of Small Nanoparticles

Abstract

Nanodiamonds containing negatively-charged triplet (having an electron spin S = 1) Nitrogen-Vacancy (NV^-) centers are an extraordinary room temperature quantum system, whose electron spins may be polarized and read out optically even in a single nanocrystal. In this report, we promote a simple but reliable method to identify, attribute and quantify these triplet defects in a polycrystalline sample using Electron Paramagnetic Resonance (EPR) spectroscopy. The characterization relies on a specific “forbidden” transition (“ΔM_S = 2”), which appears at about half the central magnetic field and shows a remarkably small anisotropy. In particular, we emphasize that this method is by far not limited to NV^- centers in diamond, but could become an important characterization tool for novel triplet defects in various types of nanoparticles.