New salt-inclusion lanthanide silicates, [K9F2][Ln(3)Si(12)O(32)] (Ln = Sm, Eu, Gd), have been synthesized using a KF-MoO3 flux, and structurally characterized by single-crystal and powder X-ray diffraction. The structures of these three isostructural compounds consist of open-branched funfer silicate single layers with six-, eight-, and twelve-membered rings, which are connected via LnO(6) octahedra to form a 3-D framework. The F- and K+ ions are located in the structural channels and form a F2K7 dimer with a structure similar to that of Cl2O7. The photoluminescence properties of the Eu compound have also been studied. The sharp peaks in the room-temperature emission spectrum are assigned and the relative intensities of the D-5(0) -> F-7(1) and 5D(0) -> F-7(2) ransitions are consistent with the crystallography results. Crystal data for the Eu compound: triclinic, space group P (1) over bar (No. 2), a = 6.8989(2) angstrom, b = 11.3834(4) angstrom, c = 11.4955(4) angstrom, alpha = 87.620(2)degrees, beta = 89.532(2)degrees, gamma = 80.221(2)degrees, and Z = 2. Crystal data for the Sm compound: The same as those for the Eu compound except a = 6.9152(6) angstrom, b = 11.400(1) angstrom, c = 11.531(1) angstrom, alpha = 87.610(1)degrees, beta = 89.445(1)degrees, and gamma = 80.081(1)degrees.