Surface photoluminescence of nanodiamonds: dependence on pH
Nanodiamonds (NDs), like other carbon nanoparticles with surfaces containing many different functional groups, have the ability to photoluminesce. In many publications, it was suggested that the reason for such photoluminescence of carbon nanoparticles is the electron trap levels caused by surface groups [1-3]. For most nanodiamonds, such surface photoluminescence is too weak for their effective use in biomedicine as photoluminescent markers. Nevertheless, certain surface groups and surrounding parameters make it possible to achieve the intensities of the NDs surface photoluminescence of the order of the intensity of the photoluminescence of NDs with color centers.
One of the parameters of the medium affecting the surface groups of NDs and, as a consequence, their surface photoluminescence, is the pH. In this work, we investigated the photoluminescence and colloidal properties of carboxylated nanodiamonds ND-COOH of various types of synthesis with a change in the pH of the medium. It was shown that a significant increase in the photoluminescence intensity with increasing pH is characteristic for carboxylated nanodiamonds of all types of synthesis and is caused by the deprotonation of the carboxyl group in the medium. However, the pH value at which this deprotonation occurs is different for different nanodiamonds. It is shown that this effect is due to the different values of the Zeta-potentials of nanodiamonds and, consequently, to the different influence of their surface charges on the values of the pH near NDs surfaces.
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Lachko A. V.
Faculty of Physics, M.V. Lomonosov Moscow State University
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