Potassium Gadolinium Phosphate with a Tunnel Structure:  Synthesis, Structure, and Optical Properties of K₃Gd₅(PO₄)₆

Abstract

A potassium gadolinium phosphate crystal, K 3 Gd 5 (PO 4 ) 6, has been synthesized by a high-temperature solution reaction and exhibits a new structural family of the alkali-metal−rare-earth phosphate system. Single-crystal X-ray diffraction analysis shows the structure to be monoclinic with space group C 2/ c and the following cell parameters: a = 17.470(3) Å, b = 6.9365(6) Å, c = 18.096(2) Å, β = 114.308(4)°, V = 1998.4(5) Å 3, Z = 4. Its structure features a three-dimensional Gd 5 (PO 4 ) 6 3- anionic framework with interesting tunnels where the K atoms are located. The framework are constructed from Gd polyhedra and isolated PO 4 tetrahedra. We have also investigated the optical properties of K 3 Gd 5 (PO 4 ) 6 in terms of the measured absorption and emission spectra.