Excitons with large binding energies in MgS/ZnSe/MgS and ZnMgS/ZnS/ZnMgS quantum wells by Urbaszek, B, Morhain, C, Bradford, C, O'Donnell, C, Telfer, SA, Tang, X, Balocchi, A, Prior, K, Cavenett, B, Townsley, C, Nicholas, R