In this work, a new Cu(I) cluster is synthesized and structurally characterized: [Cu11(TBBT)9(PPh3)6](SbF6)2 (where TBBT = 4-tert-butylbenzenethiol). This Cu(I) cluster exhibits good stability and a bright-red emission both in solution (685 nm) and in the solid state (675 nm) with a large Stokes shift (∼280 nm) under ambient conditions. Its absolute quantum yield is 0.22 in the solid state. Temperature-dependent emissions and theoretical calculations suggest that the origin of this cluster luminescence mainly results from a mixture of the metal-ligand charge transfer and the cluster-centered triplet excited states. This work not only opens new opportunities for functional applications of copper clusters but also sheds light on the structure-luminescence relationship.