Abstract
A novel orthorhombic polymorph of (NH(4),Li)Eu(MoO(4))(2) enabled by partial substitution of NH(4) with Li was synthesized via a one-pot low-temperature hydrothermal route using a Li/NH(4) precursor solution. Synchrotron X-ray powder diffraction and Rietveld refinement confirmed that this phase crystallizes in an orthorhombic lattice, representing a new structure type distinct from the known triclinic and tetragonal phases (P1 and I4(1)/a space groups). Under UV excitation, the orthorhombic ((NH(4))(1-x)Li(x))Eu(MoO(4))(2) (x = 0.074-0.172) with Pbcn space group exhibits intense red photoluminescence. The emission spectrum shows multiple sharp lines from Eu(3+) ((5)D(0) → (7)F(J)) transitions, with a dominant peak at ∼615 nm ((5)D(0) → (7)F(2)) indicative of a noncentrosymmetric Eu(3+) site environment. The pronounced crystal-field splitting of these emission lines further corroborates the Eu(3+) site symmetry deduced from the structure. This facile hydrothermal approach demonstrates an effective strategy to stabilize previously unreported polymorphs at mild conditions, underscoring its advantage in accessing new structure-property regimes for rare-earth molybdate phosphors.