Structural evolution induced preferential occupancy of designated cation sites by Eu 2+ in M5(Si3O9)2 (M = Sr, Ba, Y, Mn) phosphors

In this paper, we present new insight into a changing Eu2+ crystallographic site preference in Eu-doped M5(Si3O9)2 (M = Sr, Ba, Y, Mn), which is related to the structural variation induced by M cation substitutions. The effect of the local structural geometry on the luminescence properties of Eu2+ is revealed. By substitution of Ba2+ for Sr2+, the lattice expansion is restricted to specific cation sites, resulting in the abrupt blue shifted emission of Eu2+ ions. The abnormal blue shift on replacing Sr2+ with Mn2+ is attributed to the preferential 6-fold coordination for Mn2+ that moves the Eu2+ ions to other sites. The results elucidate the mechanisms of emission band adjustment by local site coordination change and it can be potentially extended to crystals which properties are sensitive to local lattice variations