Systematic Crystallization of NHLn(MoO) as a Family of Layered Compounds (Ln = La-Lu and Y), Derivation of LnMoO, Crystal Structure, and Photoluminescence.

NHLn(MoO) (Ln = La-Lu lanthanide, Y) was crystallized via hydrothermal reaction as a new family of layered materials, from which phase-pure LnMoO was successfully derived via subsequent annealing at 700 °C for the series of Ln elements excluding Ce and Lu. Detailed structure analysis revealed that the ionic size of Ln decisively determined the crystal structure and Mo/Ln coordination for the two families of compounds. NHLn(MoO) was analyzed to be orthorhombic ( space group, no. 60) and monoclinic (2/, no. 13) for the larger and smaller Ln of Ln = La-Gd and Ln = Tb-Lu (including Y), respectively, where both the crystal structures have a layered topology featured by the alternative stacking of a [Ln(MoO)] three-tier infinite anionic layer and interlayer NH. Four types of crystal structures were found for the LnMoO series, which are monoclinic (2/, no. 14) for Ln = La, triclinic (1̅, no. 2) for Ln = Pr-Sm, triclinic (1̅, no. 2) for Ln = Eu and Gd, and monoclini (2/, no. 14) for Ln = Tb-Yb (including Y). The photoluminescence of NHLn(MoO) (Ln = Eu, Tb) and LnMoO:Eu (Ln = La, Gd, Y) was thoroughly investigated in terms of spectral features, quantum efficiency, fluorescence decay, and CIE chromaticity. The thermal stability of luminescence was also studied for LnMoO:Eu, and the observed charge-transfer excitation components were successfully correlated with the features of the Mo-O polyhedron/unit.