What Determines the Structures of the Group 15 Elements?

Recently prepared Ce3(SiS4)2I exhibits a strong room temperature luminescence in the blue region of the visible spectrum associated to a CeIII-5d1->CeIII-4f1 electronic transition. In order to approach the emission mechanisms, the La3-xCex(SiS4) 2I family has been investigated by optical techniques at 6 and 300 K. At low temperature luminescence of the two crystallographically distinct cerium cations was evidenced along with an intrinsic luminescence of the lanthanum matrix. The influence of the halogenide on the optical properties has been studied through the substitution of iodine by chlorine and bromine which permits us to follow the increase in energy of the 4f–5d gap in the Cl