Interacting layered hydroxide nanosheets with KF leading to Y/Eu hydroxyfluoride, oxyfluoride, and complex fluoride nanocrystals and investigation of photoluminescence

Abstract

Treating nanosheets (∼4 nm thick) of RE₂(OH)₅NO₃·nH₂O layered hydroxyl nitrate (LREH-NO₃⁻, RE = Y_0.95Eu_0.05) with KF solution at a low temperature of ∼90 °C yielded F⁻-substituted LREH (RE₂(OH)₅F·nH₂O), RE(OH)_3−xF_x hydroxyfluoride (x = 1.15–1.51), and K₅RE₉F₃₂ complex fluoride depending on the F/RE molar ratio (R) used for phase conversion (R = 3 : 3–200 : 3). Calcining RE(OH)_3−xF_x of a relatively high F content (x = 1.29–1.51, R = 40 : 3–70 : 3) at 450 °C in air produced REO_(3−x)/2F_x oxyfluorides, with the F/RE molar ratio close to that of the orthorhombic structured Y₅O₄F₇ phase. Oxidation of REO_(3−x)/2F_x to form REOF and even RE₂O₃ was observed at temperatures above ∼700 °C. The materials were characterized in depth by the combined techniques of elemental analysis, XRD, FE-SEM, TEM, FTIR, and TG to reveal the process of composition, phase, and morphology evolution, and the photoluminescent properties of the resultant hydroxyfluoride, oxyfluoride and complex fluoride were also elaborated with regard to the crystal structure of the host lattice, F content, and the temperature of calcination.