ИСТИНА

It is known that the surface photoluminescence of nanodiamonds (NDs) is dependent on their surface groups. Oxygen contacting surface groups in particular are known to be a part of fluorophores not only for NDs but for the whole carbon nanoparticles family. However, when their influence on the nanodiamond fluorescence is undoubted, the precise structure and properties of NDs’ fluorophores is unknown. The change in the pH can lead to changes in the structure of the existing fluorophores without the need to compare different nanoparticles. Thus, the study of the dependence of nanodiamonds photoluminescence on the pH can shed a light on the peculiarities of the involvement of acidic surface groups in NDs fluorophores. In this study, the influence of the pH on the surface photoluminescence of 6 different oxidized nanodiamonds of various synthesis was investigated. It was found that while the dependence of the photoluminescence on the pH was complex and different for different NDs, if photoluminescence changes with pH, the changes correspond to a particular pH ranges. The measurements of NDs zeta-potentials showed that in these pH ranges the changes in the surface charge of NDs occur: surface groups became (de)protonated. The quantum mechanical calculations confirmed that photoluminescence changes correspond to the deprotonation of carboxyl –COOH and hydroxyl –OH surface groups. The mechanisms of their involvement in the structure of oxidized nanodiamonds fluorophores discussed.