  We implement our past investigations in the quark-antiquark interaction
through a non-perturbative running coupling defined in terms of a gluon mass
function, similar to that used in some Schwinger-Dyson approaches. This
coupling leads to a quark-antiquark potential, which satisfies not only
asymptotic freedom but also describes linear confinement correctly. From this
potential, we calculate the bottomonium and charmonium spectra below the first
open flavor meson-meson thresholds and show that for a small range of values of
the free parameter determining the gluon mass function an excellent agreement
with data is attained.
