Five intrinsic exciton spectra with effective exciton bandgaps lower than bulk 3C SiC are observed in 4H SiC epitaxial films grown in hot-wall reactors. In one such epitaxial film, 4H/3C/4H-SiC quantum well structures consisting of thirteen 3C-SiC bilayers are revealed by high-resolution transmission electron microscopy. The optical emission energy of this quantum well is more than 200 meV below the exciton bandgap of bulk 3C SiC. The large redshift of the optical emission is explained by the presence of a strong internal electric field in the quantum well which arises from the spontaneous polarization difference between 3C and 4H SiC.