Hydrothermal Yb³⁺-Doped NaGd(WO₄)₂ Nano- and Micrometer-Sized Crystals with Preserved Photoluminescence Properties

Abstract

Mild hydrothermal preparations using nitrate and chloride reagents as Gd3+ and Yb3+ sources lead to the synthesis of NaGd1−x Yb x (WO4)2 (0.001≤ x ≤ 0.5) particles with tetragonal scheelite-like structure phase. Nearly neutral pH ∼7.5 conditions ensure the stability of this crystalline phase over a wide range of reaction times. Synthetical routes with both kind of reagents yield basically the same particle morphology sequences, although using Gd(Yb)-chlorides the presence of nanorods is more evident, whereas using Gd(Yb)-nitrates the faster growth rate favors well-defined micrometer-sized octahedral particles. The spectroscopic properties of Yb3+ in NaGd1−x Yb x (WO4)2 synthesized micrometer-sized octahedra are equivalent to those obtained in bulk single crystals, showing a single exponential photoluminescence decay and 2F5/2 lifetime τ ≈ 330 μs for 0.001 ≤ x ≤ 0.005 doped samples. The nanoparticles and nanorods formed with Gd(Yb)-nitrates and pH < 7 by short time annealing as well as in Gd(Yb)-chloride preparations show a strong reduction of the Yb3+ lifetime with regards to that observed in micrometer-sized octahedra or in single crystals, leading to nonexponential fluorescence decays when both nano- and micrometer-sized particles coexist. The use of raw Yb2O3 with increasing purity level in the hydrothermal process yields materials that show an increase in Yb3+ lifetime toward its radiative value.

The Luminous and Magnetic Properties of Tb<SUP>3+</SUP>-Doped Four Angle Star-Like NaGd(WO<SUB>4</SUB>)<SUB>2</SUB>

“…Figure 4(a) presents the excitation and emission spectra of the NaGd(WO 4 the charge-transfer transitions within the WO 2− 4 groups. 28 Upon 273 nm excitation, NaGd(WO 4 2 shows a broad band with a maximum of 476 nm, which matches the work in Ref. [28].…”

“…28 Upon 273 nm excitation, NaGd(WO 4 2 shows a broad band with a maximum of 476 nm, which matches the work in Ref. [28]. The excitation and emission spectra of NaGd 0 99 Tb 0 01 (WO 4 2 are shown in Figure 4 The excitation band is the coalition of two broad bands.…”

Low temperature nanocasting synthesis of lanthanide ions (Ln = Tb, Eu, Dy) doped CaWO4 mesoporous structure with efficiently luminescent properties

“…All above applications are highly driven by the small particle sizes, chemical compositions, huge specific surface areas, and redox activity of metal tungstates obtained for nanoscale materials [5]. Extensive methodologies [6][7][8][9] have been performed to study the synthesis, characterization, and properties of nanoscale metal tungstates that although attractive, still face issues in efficient control over the particle size, chemical composition, surface area as well as structural specialty, and complexity that are crucial for superior physical properties. For advanced materials applications, the development of preparation techniques for mesoporous tungstate materials, showing higher surface area, controllable pore size and pore morphology, and superior interparticle connectivity compared to conventional randomly deposited nanoparticles of metal tungstates, is fundamentally important, which may help to translate the chemical language of molecular construction into the organization of various nanocrystals for certain functions.…”

Characterizations and morphology of sodium tungstate particles

“…In these conditions, the peak at 551 cm −1 can be attributed to the bending vibration of the $\text{W}{{\text{O}}_4}^{-2}$ tetrahedron [13]. The stretching vibration of the $\text{W}{{\text{O}}_4}^{-2}$ tetrahedron is observed also in the range 650–800 cm −1  [14]. The strong absorption band at 828 cm −1 originates from the O–W–O stretches of the WO 4 tetrahedron.…”