Trivalent Terbium Incorporated into Kanemite and Its Photoluminescent Property

Trivalent terbium (Tb³⁺) incorporated into Na-kanemite (Na-Ka) was firstly reported. Various characterizations, including X-ray diffraction (XRD), Scanning electron microscope equipped with energy dispersive spectroscopy (SEM/EDS), Inductively coupled plasma-mass spectrometry (ICP-MS), thermogravimetry (TG), X-ray photoelectron spectra (XPS), and Photoluminescent (PL) spectra were employed to investigate the structure, composition, morphology, and photoluminescent property of samples. XRD result indicated that the Na-Ka was an orthorhombic structure with lattice parameters of a = 7.279(3), b = 20.456(6), and c = 4.942(2)Å. After ion exchange, the product Tb-Ka showed no diffraction peaks except two weak diffraction peaks. SEM images suggested that the Tb-Ka was alike to Na-Ka in the morphology. EDS and XPS results confirmed that the Na⁺ ions in Na-Ka were almost fully replaced by Tb³⁺ ions after ion exchange. Moreover, the Tb element was uniformly distributed throughout the Tb-Ka. Photoluminescence revealed that the Tb-Ka exhibited strong emissions attributed to ⁵D₄→⁷F_J (J = 3, 4, 5, 6) transitions, and the strongest emission was at 542 nm (⁵D₄→⁷F₅). After the Tb-Ka was thermally treated at 200 ℃, 400 ℃, 600 ℃, or 800 ℃ for 2 h, the photoluminescent intensity greatly decreased. The PL decay behavior at 542 nm for both Tb-Ka and its thermally treated samples are well fitted with bi-exponential decay model. The average lifetime of 542 nm for Tb-Ka (0.990ms) was longer than those of thermally treated samples (0.709 ~ 0.767 ms). These results implied the layered kanemite was favorable for the Tb³⁺ luminescence.