Due to their high biological stability and strong fluorescence, thiolated metal nanoclusters have shown great potential as a new generation of bio-nano-materials. However, the ambiguous mechanism of fluorescence impedes the design and synthesis of highly fluorescent nanoclusters. In this work, Ag25 nanocluster and its dopants were chosen as a model to study the effect of metal synergy on the optical properties. Significantly, when the valence electrons shrank to the center of the metal kernel, an enhanced fluorescence was observed, and vice versa. This finding will hopefully make a significant contribution to the property regulations of the metal nanoclusters and stimulate more excellent applications of the luminescent nanoclusters.