  By solution of the Bethe-Goldstone equation for the Cooper pairing problem,
an approximate analytic relation is derived between coherence length xi and the
binding energy of the Cooper pair. This relation is then qualitatively
confirmed by numerically solving the corresponding self-consistent gap
equations, following the crossover from weak to strong coupling, in non-s-wave
superconductors. The relation applies to non-conventional superconductors, and
in particular to heavy Fermions and to high-Tc cuprates. Utilizing in addition
a phenomenological link between kB*Tc and a characteristic energy epsilon_c =
hbar^2 / 2m^* xi^2, with m^* the effective mass, major differences are exposed
in the functional relation between kB*Tc and epsilon_c for s-wave materials and
for non-conventional superconductors. The relation between critical temperature
and epsilon_c thereby proposed correctly reflects the qualitative properties of
heavy Fermion superconductors.
