Nanoparticles’ environment,
in particular pH, can strongly
affect their photoluminescence (PL). This can be especially true for
the surface PL of nanodiamonds (NDs) known to be dependent on the
composition of surface groups. In this paper, the effect of environmental
pH in the range from 2 to 12.5 on the surface photoluminescence of
oxidized NDs of various syntheses and surface treatments was investigated.
For the first time, the varying changes of the NDs’ PL with
the pH were shown, having, however, an essential common feature: they
were observed in the same pH regions from 2 to 5 and from 9 to 12.5,
while in the pH region from 5 to 9, the PL intensity of all samples
was almost constant. Obtained dependences of NDs’ ζ-potentials
on pH and quantum mechanical modeling showed that all changes of NDs’
PL are due to the (de)protonation of surface groups: carboxyl at pH
from 2 to 5 and hydroxyl on sp2-hybridized carbon at pH
from 9 to 12.5. The varying response of NDs’ PL to such deprotonation
shows the possibility of tuning the surface photoluminescence of NDs
for use in industry and biomedicine beyond what is possible by only
controlling the nanodiamonds’ surface groups.