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.

Recent advances in rare earth co-doped luminescent tungsten oxygen complexes

This review talks about recent advances in RE co-doped tungsten oxygen complexes, including synthesis strategies associated with the luminescent mechanism, structural features and related applications.

Scheelite like NaTb(WO4)2 nanoparticles: Green fluorescence and in vitro cell imaging applications

This study highlights the investigation of the green fluorescence in NaTb(WO₄)₂ materials (NaTbW Bulk and NaTbW Nano) synthesized via template free hydrothermal method as a function of particle size and morphology. Herein, we demonstrated the biocompatibility and intracellular green fluorescence of NaTbW Nano samples using HeLa cells for cell imaging applications. Powder X-ray diffraction studies showed that the as synthesized NaTbW Bulk and NaTbW Nano crystallize in the Scheelite like tetragonal crystal system with the I4₁/a space group. The reaction pH and solvent is observed to play a critical role in determining particle size, shape and morphology of these luminescent materials. Furthermore, size dependent optical properties were systematically studied by diffuse reflectance, steady state photoluminescence; time resolved fluorescence lifetime and quantum yield measurements. Both the materials have shown bright green fluorescence upon UV excitation as a function of particle size. Remarkable high quantum yield of NaTbW Bulk indicated its greater luminescence efficiency and the closer CIE coordinates to the commercial green illuminant suggested their potential use in solid state display systems. On the other hand the observed biocompatibility of NaTbW Nano particles towards mammalian cancer HeLa cells, Staphylococcus aureus, Escherichia coli and the intracellular green fluorescence rightly proved its functionality as active bio-probes. Thus, our work summarize the potential use of these Scheelite like NaTb(WO₄)₂ material for solid state display and bio-imaging applications.

Synthesis, functionalization and properties of uniform europium-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)2, X = Mo,W) probes for luminescent and X-ray computed tomography bioimaging

A one-pot simple procedure for the synthesis of uniform, ellipsoidal Eu³⁺-doped sodium lanthanum tungstate and molybdate (NaLa(XO₄)₂, X  = W, Mo) nanophosphors, functionalized with carboxylate groups, is described. The method is based on a homogeneous precipitation process at 120 °C from appropriate Na⁺, Ln³⁺ and tungstate or molybdate precursors dissolved in ethylene glycol/water mixtures containing polyacrylic acid. A comparative study of the luminescent properties of both luminescent materials as a function of the Eu³⁺ doping level has been performed to find the optimum nanophosphor, whose efficiency as X-ray computed tomography contrast agent is also evaluated and compared with that of a commercial probe. Finally, the cell viability and colloidal stability in physiological pH medium of the optimum samples have also been studied to assess their suitability for biomedical applications.

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.

Crystal Structure of NaLuW2O8·2H2O and Down/Upconversion Luminescence of the Derived NaLu(WO4)2:Yb/Ln Phosphors (Ln = Ho, Er, Tm)

Hydrothermally reacting Lu(NO)₃ and Na₂WO₄·2H₂O at 200 °C and pH = 8 produced the new compound NaLuW₂O₈·2H₂O, which was analyzed via the Rietveld technique to crystallize in the orthorhombic system (space group: Cmmm) with cell parameters a = 21.655(1), b = 5.1352(3), and c = 3.6320(2) Å and cell volume V = 403.87(4) ų. The crystal structure presents -(NaO₆)-(NaO₆)- and -(LuO₄(H₂O)₂WO₅)-(LuO₄(H₂O)₂WO₅)- alternating layers linked together by the O^2- ion common to NaO₆ octahedron and WO₅ triangle bipyramid. Tetragonal structured and phase-pure Na(Lu_0.87Ln_0.03Yb_0.1)(WO₄)₂ phosphors (Ln = Ho, Er, and Tm) were directly produced by calcining their NaLuW₂O₈·2H₂O analogous precursors at 600 °C for 2 h, followed by a detailed study of their downconversion/upconversion (DC/UC) photoluminescence. It was shown that the UC luminescence is dominated by a red band at ∼650 nm for Ho³⁺ (⁵F₅ → ⁵I₈ transition), green bands at ∼500-575 nm for Er³⁺ (²H_11/2/⁴S_3/2 → ⁴I_15/2 transitions) and a blue band at ∼476 nm for Tm³⁺ (¹G₄ → ³H₆ transition), all via a three-photon process. DC luminescence of the phosphors is characterized by a ∼545 nm green emission for Ho³⁺ (⁵F₄/⁵S₂ → ⁵I₈ transition, λ_ex = 453 nm), ∼500-575 nm green emissions for Er³⁺ (²H_11/2/⁴S_3/2 → ⁴I_15/2 transitions, λ_ex = 380 nm), and a ∼455 nm blue emission for Tm³⁺ (¹D₂ → ³F₄ transition, λ_ex = 360 nm), with CIE chromaticity coordinates of around (0.27, 0.71), (0.26, 0.72), and (0.15, 0.04), respectively.

Size and morphology-controlled synthesis of vernier yttrium oxyfluoride towards enhanced photoluminescence and white light emission

In this study, various shapes and sizes of vernier yttrium fluoride (Y₅O₄F₇ denoted as V-YOF) were synthesized to improve fluorescence properties.

Enhanced red luminescence and improved crystallinity in NaEu(WO4)2 phosphors: an electron beam irradiation study

Band gap engineering in NaEu(WO₄)₂ red phospors via dose-dependent EB irradiation: a new strategy for improving fluorescence intensity.

Energy transfer and colour tunability in UV light induced Tm3+/Tb3+/Eu3+: ZnB glasses generating white light emission

A promising energy transfer (Tm³⁺→Tb³⁺→Eu³⁺) approach is brought forward to generate white light emission under ultraviolet (UV) light excitation for solid state lightening. Tm³⁺/Tb³⁺/Eu³⁺ ions are combinedly doped in zinc borate glass system in view of understanding energy transfer process resulting in white light emission. Zinc borate (host) glass displayed optical and luminescence properties due to formation of Zn(II)_x-[O(-II)]_y centres in the ZnB glass matrix. At 360nm (UV) excitation, triply doped Tm³⁺/Tb³⁺/Eu³⁺: ZnB glasses simultaneously shown their characteristic emission bands in blue (454nm: ¹D₂→³F₄), green (547nm: ⁵D₄→⁷F₅) and red (616nm: ⁵D₀→⁷F₂) regions. In triple ions doped glasses, energy transfer dynamics is discussed in terms of Forster-Dexter theory, excitation & emission profiles, lifetime curves and from partial energy level diagram of three ions. The role of Tb³⁺ in ET from Tm³⁺→Eu³⁺ was discussed using branch model. From emission decay analysis, energy transfer probability (P) and efficiency (η) were evaluated. Colour tunability from blue to white on varying (Tb³⁺, Eu³⁺) content is demonstrated from Commission Internationale de L'Eclairage (CIE) chromaticity coordinates. Based on chromaticity coordinates, other colour related parameters like correlated colour temperature (CCT) and colour purity are also computed for the studied glass samples. An appropriate blending of such combination of rare earth ions could show better suitability as potential candidates in achieving multi-colour and warm/cold white light emission for white LEDs application in the field of solid state lightening.

Evolution of hollow nanostructures in hybrid Ce1-x Cu x O2 under droplet confinement leading to synergetic effects on the physical properties

The paper discusses a successful strategy for tuning the hollow, porous or even solid morphologies of pure and Cu²⁺-doped CeO₂ nanostructures. The reaction of nanodroplets at the interface in miniemulsions is significantly affected by the concentration of dopants. The growth mechanism is both reaction- as well as diffusion-controlled, which finally determines the particular morphology. With a varying degree of dopant concentration and quantum confinement, the concentration of Ce³⁺ available on the surface of the nano-droplets and -particles is found to change quite appreciably. This immediately leads to modulation in the physical properties, such as ferromagnetism or absorption. The significant red shift in the absorption spectra and associated broadband visible photoluminescence opens newer applications for the present material in visible optoelectronic devices.

Assembly of 1D coaxial nanoribbons into 2D multicolor luminescence array membrane endowed with tunable anisotropic electrical conductivity and magnetism via electrospinning

A flexible 2D color-tunable coaxial nanoribbon array membrane with anisotropic electrical conductivity and magnetism is successfully fabricated via one-pot electrospinning.

Multidoped Ln3+ gadolinium dioxycarbonates as tunable white light emitting phosphors

Gadolinium dioxycarbonates co-doped with different visible emitting lanthanides were synthesized via a co-precipitation method using oxalic acid as a precipitating agent.

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.

Multi-color luminescence properties and energy transfer behaviour in host-sensitized CaWO4:Tb3+,Eu3+phosphors

A series of host-sensitized and color-tunable CaWO₄:Tb³⁺,Eu³⁺phosphors have been successfully synthesizedviathe high-temperature solid-state reaction route and their photoluminescence properties and energy transfer mechanism have been carefully investigated.

Structural, optical and special spectral changes of Dy3+ emissions in orthovanadates

This paper reports on the structural, optical and photometric characterization of yttrium gadolinium orthovanadates (Y_1−xGd_xVO₄) doped with Dy³⁺ for white emission in solid state lighting.

White-light-emitting properties of SrTiO3:Pr3+ nanoparticles

White-light emission from SrTiO₃:Pr³⁺ nanoparticles has been achieved by tuning combination of the ³P₀ and ¹D₂-related blue to red emissions.

Tunable white-light emission via energy transfer in single-phase LiGd(WO4)2:Re3+ (Re = Tm, Tb, Dy, Eu) phosphors for UV-excited WLEDs

Novel single-phase white-light-emitting phosphors have been successfully synthesized by a solid-state reaction and their photoluminescence properties and energy transfer mechanism have been carefully investigated.

Up/down conversion, tunable photoluminescence and energy transfer properties of NaLa(WO4)2:Er3+,Eu3+ phosphors

A series of novel, color-tunable, single-component NaLa(WO₄)₂:Er³⁺,Eu³⁺ phosphors were prepared by a one-step hydrothermal method. The energy transfer mechanism was studied, and color-tunable emissions in NaLa(WO₄)₂ are realized.

A physicochemical process for fabricating submicrometer hollow fluorescent spheres of Tb3+-incorporated calcium phosphate

The submicrometer hollow fluorescent spheres of Tb³⁺-incorporated calcium phosphate (CaP) were successfully fabricated by pulsed laser irradiation of the dispersion of carbon-integrated hydroxyapatite (HAp) nanopowders into Tb³⁺ ethanol solution.

A new single-phase white-light-emitting CaWO4:Dy3+ phosphor: synthesis, luminescence and energy transfer

A new single-phase white-emitting CaWO₄:Dy³⁺ phosphor has been successfully synthesized and the photoluminescence properties and energy-transfer mechanism have been carefully investigated.

Luminescence, energy-transfer and tunable color properties of single-component Tb3+ and/or Sm3+ doped NaGd(WO4)2 phosphors with UV excitation for use as WLEDs

Tb³⁺ and/or Sm³⁺ codoped NaGd(WO₄)₂ microcrystals were prepared and energy transfer mechanisms of WO₄²⁻ → Sm³⁺ and Tb³⁺ → Sm³⁺ were studied. The color-tunable emissions are investigated, for nUV-LED applications.