Crystal Structure of NaLuWO·2HO and Down/Upconversion Luminescence of the Derived NaLu(WO):Yb/Ln Phosphors (Ln = Ho, Er, Tm).

Hydrothermally reacting Lu(NO) and NaWO·2HO at 200 °C and pH = 8 produced the new compound NaLuWO·2HO, which was analyzed via the Rietveld technique to crystallize in the orthorhombic system (space group: Cmmm) with cell parameters a = 21.655(1), b = 5.1352(3), and c = 3.6320(2) Å and cell volume V = 403.87(4) Å. The crystal structure presents -(NaO)-(NaO)- and -(LuO(HO)WO)-(LuO(HO)WO)- alternating layers linked together by the O ion common to NaO octahedron and WO triangle bipyramid. Tetragonal structured and phase-pure Na(LuLnYb)(WO) phosphors (Ln = Ho, Er, and Tm) were directly produced by calcining their NaLuWO·2HO analogous precursors at 600 °C for 2 h, followed by a detailed study of their downconversion/upconversion (DC/UC) photoluminescence. It was shown that the UC luminescence is dominated by a red band at ∼650 nm for Ho (F → I transition), green bands at ∼500-575 nm for Er (H/S → I transitions) and a blue band at ∼476 nm for Tm (G → H transition), all via a three-photon process. DC luminescence of the phosphors is characterized by a ∼545 nm green emission for Ho (F/S → I transition, λ = 453 nm), ∼500-575 nm green emissions for Er (H/S → I transitions, λ = 380 nm), and a ∼455 nm blue emission for Tm (D → F transition, λ = 360 nm), with CIE chromaticity coordinates of around (0.27, 0.71), (0.26, 0.72), and (0.15, 0.04), respectively.