Clusters based on the cubic, hexanuclear rhenium(III) core [Re-6(mu(3)-Q)(8)](2+) (Q = S, Se) emit red phosphorescence with microsecond-scale lifetimes. Emission quantum yields of 16 clusters range from 1% to 23%; those having O-bound terminal ligands feature the highest yields and the longest liftimes. Certain clusters are photolabile, with medium-sensitive emissive properties. When photodecomplexation is suppressed, all clusters herein obey the energy gap law, indicating excitation confined to the [Res(6)Q](2+) core.