Eu³⁺/Tb³⁺-Doped La₂O₂CO₃/La₂O₃ Nano/Microcrystals with Multiform Morphologies: Facile Synthesis, Growth Mechanism, and Luminescence Properties

Abstract

LaCO(3)OH nano/microcrystals with a variety of morphologies/sizes including nanoflakes, microflowers, nano/microrhombuses, two-double microhexagrams sandwichlike microspindles, and peach-nucleus-shaped microcrystals have been synthesized via a facile homogeneous precipitation route under mild conditions. A series of controlled experiments indicate that the pH values in the initial reaction systems, carbon sources, and simple ions (NH(4)(+) and Na(+)) were responsible for the shape determination of the LaCO(3)OH products. A possible formation mechanism for these products with diverse architectures has been presented. After annealing at suitable temperatures, LaCO(3)OH was easily converted to La(2)O(2)CO(3) and La(2)O(3) with the initial morphologies. A systematic study on the photoluminescence and cathodoluminescence properties of Eu(3+)- or Tb(3+)-doped La(2)O(2)CO(3)/La(2)O(3) samples has been performed in detail. The excitation and site-selective emission spectra were recorded to investigate the microstructure, site symmetry, and difference in the (5)D(0) → (7)F(2) transition of Eu(3+) ions in La(2)O(2)CO(3) and La(2)O(3) host lattices. In addition, the dependence of the luminescent intensity on the morphology for the as-prepared La(2)O(2)CO(3)/La(2)O(3):Ln(3+) (Ln = Eu, Tb) samples has been investigated. The ability of generating diverse morphologies and multiemitting colors for different rare-earth activator ion (Ln = Eu, Tb) doped La(2)O(2)CO(3)/La(2)O(3) nano/microstructures provides a great opportunity for the systematic evaluation of morphology-dependent luminescence properties, as well as the full exploration of their application in many types of color display fields.

Hydrothermal Synthesis of LaCO3OH and Ln3+-doped LaCO3OH Powders under Ambient Pressure and Their Transformation to La2O2CO3and La2O3

“…DTA curves showed that reactions (2) and (3) were endothermic. In addition, the endothermic peak for reaction (2) appeared at higher temperature for o-LaCO 3 OH than for h-LaCO 3 OH, whereas the opposite was observed for reaction (3). Figure 3 shows IR spectra of the h-and o-LaCO 3 OH powders.…”

“…11 LaCO 3 OH powders have been also prepared by a hydrothermal reaction in an autoclave using the following reagents: LaCl 3 and thiourea, 12,13 La(NO 3 ) 3 and urea, 4,14 La(NO 3 ) 3 , glucose, and acrylamide, 15 La 2 O 3 and glycine, 16 LaCl 3 and gelatin, 17 La(oleate) 3 and aqueous tertbutylamine, 18 La…”

“…LaCO 3 OH powders can also be prepared by a hydrothermal reaction without the need for an autoclave, 3,21 as for LaFCO 3 powders. 22 To date, there are still no reports on the factors determining the polymorph of LaCO 3 OH powders obtained by a hydrothermal reaction under ambient pressure.…”

“…The effects of the reaction temperature, inorganic salt additive, species of Ln 3+ dopant, and solvent on the polymorph of LaCO 3 OH powders were investigated. Urea is used widely as the precipitation reagent of metal ions because it thermally decomposes into NH 3 and CO 3 2− ions in neutral and basic aqueous solutions. 23 The as-prepared LaCO 3 OH powders were characterized by powder X-ray diffraction (XRD), Fourier transformation infrared (IR) spectroscopy, thermogravimetric (TG) and differential thermal analysis (DTA), and fieldemission scanning electron microscopy (FE-SEM Characterization.…”

“…Trivalent lanthanide (Ln 3+ ) ions have high affinity to the carbonate (CO 3 2− ) ion, as evidenced by the occurrence of stable minerals such as (La,Ce, Nd) 2 (CO 3 ) 3 ·8H 2 O (lanthanite), (La,Ce) 2 (CO 3 ) 3 ·4H 2 O (calkinsite), and (La,Ce)(F,OH)CO 3 (bastnaesite).…”