Crystal growth, structure determination, and optical properties of new potassium-rare-earth silicates K 3RESi 2O 7 ( RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)

Abstract

Single crystals of K 3 RESi 2O 7 ( RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were grown from a potassium fluoride flux. Two different structure types were found for this series. Silicates containing the larger rare earths, RE=Gd, Tb, Dy, Ho, Er, Tm, Yb crystallize in a structure K 3 RESi 2O 7 that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment, while in K 3LuSi 2O 7, containing the smallest of the rare earths, lutetium is found solely in an octahedral coordination environment. The structure of K 3LuSi 2O 7 crystallizes in space group P6 3/ mmc with a=5.71160(10) Å and c=13.8883(6) Å. The structures containing the remaining rare earths crystallize in the space group P6 3/ mcm with the lattice parameters of a=9.9359(2) Å, c=14.4295(4) Å, (K 3GdSi 2O 7); a=9.88730(10) Å, c=14.3856(3) Å, (K 3TbSi 2O 7); a=9.8673(2) Å, c=14.3572(4) Å, (K 3DySi 2O 7); a=9.8408(3) Å, c=14.3206(6) Å, (K 3HoSi 2O 7); a=9.82120(10) Å, c=14.2986(2) Å, (K 3ErSi 2O 7); a=9.80200(10) Å, c=14.2863(4) Å, (K 3TmSi 2O 7); a=9.78190(10) Å, c=14.2401(3) Å, (K 3YbSi 2O 7). The optical properties of the silicates were investigated and K 3TbSi 2O 7 was found to fluoresce in the visible.