Crystal structure and fluorescence lifetime of potassium neodymium orthophosphate, K3Nd(PO4)2, a new laser material

Crystals of a new high-Nd-concentration laser material, K3Nd(PO4)2, have been grown both from the melt and from a KF-KCl flux. Singlecrystal x-ray diffraction analysis shows the structure to be monoclinic with space group P21m, Z = 2, and cell parameters a = 9.532(2) Å, b = 5.631(3) Å, c = 7.444(3) Å, β = 90.95(2)°, giving a Nd concentration of 5.00 × 1021 cm−3. The basic structural units are isolated PO4 tetrahedra and isolated NdO7 decahedra. The NdO7 decahedra each connect six PO4 tetrahedra to form two-dimensional Nd(PO4)23− sheets in the a-b plane, with K atoms inserted along the c-axis between these sheets. Each PO4 tetrahedron is connected to three NdO7 decahedra; half the tetrahedra share an edge with a decahedron, giving a short Nd-Nd separation of 4.873 Å. Of the seven O ions surrounding each Nd ion, six are near inversion positions. The radiative lifetime of Nd3+ ions in this structure is quite long because of the small deviation from inversion symmetry, but concentration quenching is much stronger than in other structures with isolated Nd-O polyhedra. The measured fluorescence lifetime decreases from 460 μsec in K3Nd0.005La0.995(PO4)2 to 21 μsec in K3Nd(PO4)2.