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Crystal Structure of NaLuW2O8·2H2O and Down/Upconversion Luminescence of the Derived NaLu(WO4)2:Yb/Ln Phosphors (Ln = Ho, Er, Tm)
journal contribution
posted on 2018-08-15, 19:51 authored by Xiaofei Shi, Maxim S. Molokeev, Xuejiao Wang, Zhihao Wang, Qi Zhu, Ji-Guang LiHydrothermally reacting Lu(NO)3 and Na2WO4·2H2O at
200 °C and pH = 8 produced the new compound NaLuW2O8·2H2O, 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) Å3.
The crystal structure presents −(NaO6)-(NaO6)– and −(LuO4(H2O)2WO5)-(LuO4(H2O)2WO5)– alternating layers linked together by the
O2– ion common to NaO6 octahedron and
WO5 triangle bipyramid. Tetragonal structured and phase-pure
Na(Lu0.87Ln0.03Yb0.1)(WO4)2 phosphors (Ln = Ho, Er, and Tm) were directly produced
by calcining their NaLuW2O8·2H2O 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 Ho3+ (5F5 → 5I8 transition), green bands at ∼500–575
nm for Er3+ (2H11/2/4S3/2 → 4I15/2 transitions) and
a blue band at ∼476 nm for Tm3+ (1G4 → 3H6 transition), all via a
three-photon process. DC luminescence of the phosphors is characterized
by a ∼545 nm green emission for Ho3+ (5F4/5S2 → 5I8 transition, λex = 453 nm), ∼500–575
nm green emissions for Er3+ (2H11/2/4S3/2 → 4I15/2 transitions, λex = 380 nm), and a ∼455 nm
blue emission for Tm3+ (1D2 → 3F4 transition, λex = 360 nm),
with CIE chromaticity coordinates of around (0.27, 0.71), (0.26, 0.72),
and (0.15, 0.04), respectively.