Solid solution between lithium-rich yttrium and europium molybdate as new efficient red-emitting phosphors

Abstract

Li_3.5Y_1.5(MoO₄)₄ was synthesized in the form of phase-pure crystals. It forms a solid solution with Li_3.5Eu_1.5(MoO₄)₄. Single crystals obtained from Li₂MoO₄ fluxes had edge lengths of up to 0.5 mm. The crystal structures of Li_3.5(Y_1−xEu_x)_1.5(MoO₄)₄ (x = 0, 0.1, 0.25, 0.5, 0.75 and 1) were determined in the triclinic crystal system (e.g. P, no. 2, Z = 1; Li_3.5Y_1.5(MoO₄)₄: a = 5.1875(2) Å, b = 6.6380(2) Å, c = 10.2731(4) Å, α = 100.082(3)°, β = 100.257(2)° and γ = 111.943(2)°). All the compounds are isostructural and crystallize with a structure related to the scheelite-type structure with mixed occupancy of one cation position, while the two others are occupied by Li ions exclusively. Thermal analyses reveal stability in air up to 995 K for Li_3.5Y_1.5(MoO₄)₄; the decomposition temperature decreases with an increase in Eu-content. Spectroscopic properties (emission and excitation) were investigated in the context of the search for new thermographic phosphors. Excitation at 395 nm leads to strong red emission at 613 nm. Features of the emission spectra suggest the potential of Li_3.5(Y_1−xEu_x)_1.5(MoO₄)₄ as red phosphor candidates for light emitting diodes. Their luminescence properties at high temperatures were also investigated.