Hydrothermal synthesis and luminescence behavior of rare-earth-doped NaLa(WO4)2 powders

Low-temperature synthesis of NaRE(WO4)2 films via anion exchange from Layered rare-earth hydroxides (LRHs) films, phase/morphology evolution and photoluminescence

Alkaline lanthanide tungstates NaRE(WO4)2 (RE = La-Ho, and Y) films were hydrothermally synthesized via anion exchange using the electrodeposited layered rare-earth hydroxide (RE2(OH)5NO3·nH2O) films as precursor template in the presence...

Judd-Ofelt spectroscopic properties of Er3+-doped NaLa(WO4)2 polycrystalline powder

Er³⁺-doped NaLa(WO₄)₂ is a promising phosphor material for applications in many fields including the ratiometric thermometry based on thermal effect of fluorescence intensity ratio (FIR) of green fluorescence of Er³⁺, which is directly correlated with Judd-Ofelt parameters Ω_i (i = 2, 4, 6). Present paper reports synthesis and Judd-Ofelt spectroscopic properties of Er³⁺-doped NaLa(WO₄)₂ µm-sized phosphor. The phosphor was synthesized by solid-state chemical reaction and characterized by X-ray diffraction and Raman scattering techniques. The results show that the phosphor is dominated by NaLa(WO₄)₂ crystalline phase and has a maximum phonon energy 927 cm^-1. Judd-Ofelt analysis was done for the phosphor using a safe, reliable method based on diffuse reflection spectrum and Er³⁺ 1.5 μm fluorescence lifetime. First, diffuse reflection spectrum of the phosphor was measured and relative absorption spectrum was calibrated from it using Kubelka-Munk theory. Second, Er³⁺ 1.5 μm fluorescence lifetime of the phosphor was measured and absorption cross-section spectrum was obtained based on the assumption that the 1.5 μm emission has 100% quantum efficiency. Finally, based on the absorption cross-section spectrum, standard Judd-Ofelt analysis was carried out to extract the Ω_i. Radiative rate, fluorescent branch ratio and radiative lifetime of some transitions have been obtained from the known Ω_i values. In addition, FIR proportional factor was evaluated in terms of Ω_i and compared with those values of other materials. The result shows that the phosphor has a better prospect for the application in ratiometric thermometry.

NaLaW2O7(OH)2(H2O): Crystal Structure and RE3+ Luminescence in the Pristine and Annealed Double Tungstates (RE = Eu, Tb, Sm, and Dy)

Hydrothermal reaction of La(NO₃)₃ and Na₂WO₄·2H₂O at 100 °C and pH 8 resulted in the formation of new compound NaLaW₂O₇(OH)₂(H₂O), as confirmed by the X-ray diffraction results, chemical composition, Fourier transform infrared, thermogravimetric/differential thermal analysis, and transmission electron microscopy analyses. The crystal structure was determined in the triclinic system (space group P1̅), with lattice constants a = 5.8671(2) Å, b = 8.2440(2) Å, and c = 9.0108(3) Å, axis angles α = 93.121(2)°, β = 75.280(2)°, and γ = 94.379(2)°, and cell volume V = 420.03(2) ų. The structure contains two-dimensional layers of -(W1O₆)-(W1O₆)-(W2O₆)-(W2O₆)-(W1O₆)-(W1O₆)- and -LaO₉-LaO₉- chains alternating in the a-b plane, which are linked together through NaO₆ octahedral trigonal prisms by edges to form a three-dimensional net. Dehydration of the compound proceeds up to a low temperature of ∼350 °C and results in the formation of technologically important NaLa(WO₄)₂ double tungstate, which is thus a unique precursor for the latter. Na(La,RE)W₂O₇(OH)₂(H₂O) and Na(La,RE)(WO₄)₂ solid solutions separately doped with the practically important activators for which RE = Eu, Tb, Sm, and Dy were also successfully synthesized and investigated for their structural features and photoluminescence properties, including excitation, emission, quantum yield, emission color, and fluorescence decay kinetics. The compounds were shown to exhibit dominantly strong red (∼616 nm for Eu³⁺; λ_ex = 395 or 464 nm), green (∼545 nm for Tb³⁺; λ_ex = 278 or 258 nm), deep red (∼645 nm for Sm³⁺; λ_ex = 251 nm), and yellow (∼573 nm for Dy³⁺; λ_ex = 254 nm) emission upon being irradiated with the peak wavelengths of their strongest excitation bands.

Novel red-emitting LiGd(WO4)2:Eu3+phosphor with high thermal stability and high color purity for application in white light-emitting diodes

Novel red-emitting LiGd(WO₄)₂:Eu³⁺phosphors with high thermal stability and high color purity have been developed for ultraviolet-excited white light-emitting diodes.

Structural, vibrational study and UV photoluminescence properties of the system Bi(2−x)Lu(x)WO6 (0.1 ≤ x ≤ 1)

This study on bismuth lutetium tungstates presents, for the first time, correlations between structure, vibrational and photoluminescence properties in the case of solid solutions Bi_2−xLuxWO₆. The origin of luminescence signals under UV excitation is discussed.

Pure-phase La2(WO4)3:Eu3+ nanocrystals and spindle-like NaLa(WO4)2:Yb3+/Er3+ nano/microcrystals: selective synthesis, morphologies and photoluminescent properties

The selective synthesis of pure-phase La2(WO4)3 nanocrystals and uniform spindle-like NaLa(WO4)2 nano/microcrystals with tunable size based on one reaction system has been reported for the first time. The sodium ion is crucial for the selective synthesis of La2(WO4)3 and NaLa(WO4)2. An additional hydrothermal treatment has a great effect on the morphology of La2(WO4)3, while the hydrothermal temperature and time, and the amount of glycerine, significantly influence the morphology and size of NaLa(WO4)2. Based on the time-dependent experiments, it is proposed that the Ostwald ripening is the formation mechanism of the spindle-like NaLa(WO4)2. The resultant La2(WO4)3:Er(3+) nanocrystals can emit a bright red color with a high purity under the excitation of 467 nm (blue region) and, more importantly, it can be easily dispersed in distilled water. The up-conversion emission intensity of NaLa(WO4)2:Yb(3+)/Er(3+) is increased rapidly with the Yb(3+) concentration under 980 nm laser excitation, suggesting the efficient energy transfer from Yb(3+) to Er(3+). Moreover, the emission color can be tuned from chartreuse to green by increasing the Yb(3+) concentration. These unique properties of La2(WO4)3 and NaLa(WO4)2 are closely related with their distinctive crystal structures, and it is anticipated that the findings in this work may give an insight into the fabrication and application of the rare earth tungstates.