The luminescence properties of Eu3+‐activated disilicates (Y, Tb)2Si2O7 are strongly influenced by their crystal structure. Within the region of type C in cathodoluminescence an energy transfer from the hole trap Tb3+ to the electron trap Eu3+ is working due to the crystallographic equivalence of the Ln3+ surroundings. However, in disilicates of type B with four inequivalent Ln3+ positions and additionally large variations in the shape of the coordination polyhedra the energy transfer is blocked, resulting in a strong reduction of the efficiency. The mechanisms of energy transfer are discussed.