Metal (M)-encapsulated clusters of Ge and Sn, Zn@Ge12 and Cd@Sn12, are obtained from total energy calculations using ab initio pseudopotential plane wave method and generalized gradient approximation for the exchange-correlation energy. These have perfect icosahedral symmetry and large highest occupied-lowest unoccupied molecular orbital gap of about 2 eV. It lies in the optical region and makes these species attractive for cluster assembled optoelectronic materials. Calculations on silicon clusters doped with Be show a different behavior. {\textcopyright} 2002 American Institute of Physics.