Crystal Structure of NaLuW2O8 center dot 2H(2)O and Down/Upconversion Luminescence of the Derived NaLu(WO4)(2):Yb/Ln Phosphors (Ln = Ho, Er, Tm)

Shi, Xiaofei; Molokeev, Maxim S.; Wang, Xuejiao; Wang, Zhihao; Zhu, Qi; Li, Ji-Guang Source: INORGANIC CHEMISTRY, 57 (17):10791-10801; 10.1021/acs.inorgchem.8b01427 SEP 3 2018

Hydrothermally 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+ (5F55I8 transition), green bands at ∼500–575 nm for Er3+ (2H11/2/4S3/24I15/2 transitions) and a blue band at ∼476 nm for Tm3+ (1G43H6 transition), all via a three-photon process. DC luminescence of the phosphors is characterized by a ∼545 nm green emission for Ho3+ (5F4/5S25I8 transition, λex = 453 nm), ∼500–575 nm green emissions for Er3+ (2H11/2/4S3/24I15/2 transitions, λex = 380 nm), and a ∼455 nm blue emission for Tm3+ (1D23F4 transition, λex = 360 nm), with CIE chromaticity coordinates of around (0.27, 0.71), (0.26, 0.72), and (0.15, 0.04), respectively.