  We present a detailed investigation of excitonic absorption in
$Zn_{0.69}Cd_{0.31}Se/ZnSe$ quantum wells under the application of a
perpendicular magnetic field. The large energy separation between heavy- and
light-hole excitons allows us to clearly resolve and identify magneto-excitonic
absorption resonant with the continuum edge of the 1S heavy-hole exciton.
Experimental values of the exciton binding energy are compared with results of
a theoretical model that includes the exciton-phonon interaction. The
remarkable agreemeent found unambiguously indicates the predominant polaronic
character of excitons in ZnSe-based heterostructures.
