The stability of large ligated copper(I) clusters of undeca- and dodecanuclearity encapsulating iodide and stabilized by dithio- and diseleno-phosph(in)ates was investigated by density functional theory (DFT) calculations. A bonding analysis is provided, which shows strong iono-covalent bonding between the iodide and its host. The electronic structures of the title compounds suggest the possibility for interesting photoluminescent properties, which were fully investigated by time-dependent DFT calculations including vibronic contributions to simulate the phosphorescence spectra. The quantum mechanical results were compared to the experimental data obtained for the new clusters [Cu11(μ9-I)(μ3-I)3{Se2P(OiPr)2}6]+ and [Cu11(μ9-I)(μ3-I)3(Se2PPh2)6]+, whose syntheses, X-ray structures, and full characterizations are reported in this paper. From this combined theoretical/experimental investigation, it is suggested that the encapsulation by the same copper(I) cages of a formally Cu- anion is also possible. DFT calculations on these species are consistent with the existence of stable two-electron superatoms.