Li 2 BaMgP 2 O 8 and Na 2 BaMgP 2 O 8 were synthesized by a standard solid state reaction. Structural analyses have revealed that Li 2 BaMgP 2 O 8 is a member of the olgite family, as is the case with Na 2 BaMgP 2 O 8 . The layer-framework build up by corner-sharing MgO 6 octahedra and PO 4 tetrahedra twists around C 3 axes to match the size of B-site cation (Li + or Na + ). This twisting affects the coordination number for the B-site cation and unit cell size.Eu-doped Li 2 BaMgP 2 O 8 and Na 2 BaMgP 2 O 8 exhibited intense violet–blue emission under ultraviolet excitation. They were characterized by two emission centers; Eu 2+ ions replacing A-site cations (Ba 2+ ) and B-site cations (Li + or Na + ). The B-site Eu 2+ emission was very sensitive to the twisting behavior caused by original B-site cation.