Salt-coated air oxidation nanodiamond surface purification with a photoluminescence spectroscopy quality control

Emerging fields of quantum technologies and biomedical applications demand pure nanodiamonds (NDs) with well-defined surface chemistry. Therefore, an inexpensive, scalable and eco-friendly ND surface purification technology is required. In this study, we report our method, salt-coated air oxidation (SCAO) thermal annealing, to achieve uniform purification of a ND surface without the loss of diamond material. A photoluminescence (PL) spectroscopy quality control method is proposed to evaluate the degree of purification. The presence of an isoemission point in the set of nitrogen vacancy (NV) center PL spectra, obtained through the photochromic effect, is examined as a surface purity indicator. The ratio of the NV centers in NDs after the SCAO treatment was determined by decomposing the PL spectra using the non-negative matrix factorization technique.