NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties

Frequency upconversion based thermally stable molybdate phosphors in temperature sensing probe

Er3+-Yb3+ co-doped NaGd(MoO4)2 phosphors with different concentrations of Er3+ and Yb3+ ions have been successfully synthesized via a high-temperature solid-state reaction method. Phase confirmation and morphological studies have been done...

NaY(MoO4)2-based nanoparticles: synthesis, luminescence and photocatalytic properties

We report on a novel synthesis method, which produces NaY(MoO₄)₂ nanoparticles having an almost spherical shape and hydrophilic character. The procedure is also suitable for the preparation of NaY(MoO₄)₂-based nanophosphors by doping this host with lanthanide cations (Eu³⁺, Tb³⁺ and Dy³⁺), which, under UV illumination, exhibit intense luminescence whose color is determined by the selected doping cation (red for Eu³⁺, green for Tb³⁺ and yellow for Dy³⁺). The effects of the cations doping level on the luminescent properties are analyzed in terms of emission intensities and luminescent lifetime, to find the optimum phosphors. Finally, the performance of these nanophosphors and that of the undoped system for the photocatalytic degradation of rhodamine B, used as a model compound, is also analyzed.

Enhancing the static green up-conversion luminescence of NaY(MoO4)2:Yb/Er microcrystals via an annealing strategy for anti-counterfeiting applications

The majority of the fabrication procedures of lanthanide-doped materials involve thermal treatment that often results in crystallite regrowth, stabilizing the specific crystal structure and resulting in luminescence enhancement. The efficiency and intensity of up-conversion luminescence are closely related to the structure and synthesis process of the materials. Herein, well-crystallized and pure tetragonal NaY(MoO4)2 microcrystals with a uniform octahedral shape have been successfully synthesized via an environmentally friendly hydrothermal method, followed by annealing treatment. The phases, structures, morphologies, and compositions of the synthesized products annealed at 500-1000 °C remain unchanged, indicating high thermal stability. Furthermore, the NaY(MoO4)2:Yb3+/Er3+ microcrystals exhibit strong green emission when irradiated using infrared (980 nm) or ultraviolet (378 nm) wavelengths. Upon 980 nm excitation, up to 37-fold luminescence enhancement is achieved when the samples are annealed at about 700 °C. Interestingly, the high colour purity of the strong green emission is not only independent of the dopant concentration and heat treatment temperature, but it is also independent of the excitation conditions, including power and wavelength, and this makes it particularly suitable as a green safety signal light and luminescent security ink in paintings. As-prepared safety inks with NaY(MoO4)2:Yb3+/Er3+ microcrystals were used for visual fingerprint recognition printed on A4 paper with three-level fingerprint security features, significantly increasing the difficulty of illegal imitation and enhancing the levels of anti-counterfeiting.

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.

Low-Temperature Solid-State Synthesis and Upconversion Luminescence Properties in (Na/Li)Bi(MoO4)2:Yb3+,Er3+ and Color Tuning in (Na/Li)Bi(MoO4)2:Yb3+,Ho3+,Ce3+ Phosphors

In this Article, we reported the synthesis and the upconversion luminescence (UCL) properties of a series of novel (Na/Li)Bi(MoO₄)₂:Yb³⁺,Er³⁺ [(N/L)BMO:Yb³⁺,Er³⁺] and (Na/Li)Bi(MoO₄)₂:Yb³⁺,Ho³⁺,Ce³⁺ [(N/L)BMO:Yb³⁺,Ho³⁺,Ce³⁺] phosphors. X-ray diffraction patterns and Rietveld refinements for several representative samples indicated the pure phase of as-prepared samples. The Yb³⁺,Er³⁺ codoped (N/L)BMO presented bright green luminescence under 975 nm laser excitation with UCL spectra showing two main green bands around 529 nm (Er³⁺, ²H_11/2 → ⁴I_15/2) and 551 nm (Er³⁺, ⁴S_3/2 → ⁴I_15/2), in addition to a very weak one at 655 nm (Er³⁺, ⁴F_9/2 → ⁴I_15/2). The (N/L)BMO:Yb³⁺,Ho³⁺ mainly showed a green band around 544 nm (⁵S₂,⁵F₄ → ⁵I₈) and a red band around 654 nm (⁵F₅ → ⁵I₈) upon 975 nm laser excitation. With increasing Yb³⁺ concentrations in (N/L)BMO:Yb³⁺,0.01Ho³⁺, the red/green ratios decreased monotonously corresponding to the emission color variation from light red to light yellow. Both UCL mechanisms of Yb³⁺,Er³⁺ and Yb³⁺,Ho³⁺ were determined to be two-phonons absorption processes in (N/L)BMO:Yb³⁺,Er³⁺/Ho³⁺. The Ce³⁺ ions were introduced into Yb³⁺,Ho³⁺ codoped (N/L)BMO to show the color tuning from light yellow to light red originating from the cross relaxation processes of (CR1) Ho³⁺ (⁵F₄,⁵S₂) + Ce³⁺ (²F_5/2) → Ho³⁺ (⁵F₅) + Ce³⁺ (²F_7/2) and (CR2) Ho³⁺(⁵I₆) + Ce³⁺ (²F_5/2) → Ho³⁺ (⁵I₇) + Ce³⁺ (²F_7/2), which is based on the energy matching of Ce³⁺²F_7/2-²F_5/2 level pairs with Ho³⁺⁵I₆-⁵I₇ and ⁵F₄,⁵S₂-⁵F₅ level pairs and confirmed by the decay times. These results suggest good UCL properties of (N/L)BMO:Yb³⁺, Er³⁺ and (N/L)BMO:Yb³⁺, Ho³⁺, Ce³⁺ materials, and color modulation is easily controlled by varying Yb³⁺ concentration and a cross relaxation process between Ce³⁺ and Ho³⁺, which provides efficient methods to regulate the emission color of UCL phosphors.

Multifunctional BiF3:Ln3+ (Ln = Ho, Er, Tm)/Yb3+ nanoparticles: an investigation on the emission color tuning, thermosensitivity, and bioimaging

Pure cubic phase and uniform BiF₃:Ln³⁺ (Ln = Ho, Er, Tm)/Yb³⁺ nanoparticles (NPs) were prepared by coprecipitation. The growth mechanism of BiF₃:2%Er³⁺/20%Yb³⁺ NPs was proposed based on evolution analysis of the time-dependent morphology, in which BiF₃:2%Er³⁺/20%Yb³⁺ was formed through the growth process of “nucleation to crystallization and Ostwald ripening”. The upconversion luminescence (UCL) properties and mechanism of BiF₃:Ln³⁺ (Ln = Ho, Er, Tm)/Yb³⁺ under dual-wavelength excitation were also systematically investigated. The emission intensity of BiF₃:2%Er³⁺/20%Yb³⁺ by dual-wavelength excitation (λ = 980 nm + 1550 nm) was 1.49 times more than that excited by 1550 nm or 980 nm individually. Furthermore, the properties of the bright white and multicolor UCL showed that yellow, purple, green, or pinkish light could be observed by controlling the doping concentration of Ln³⁺ (Ln = Yb, Er, Tm, and Ho), indicating that they had potential applications in backlight sources of color displays and security labeling. The temperature sensitivity of BiF₃:2%Er³⁺/20%Yb³⁺ exhibited a downward tendency and its max value was about 0.0036 K⁻¹ at 273 K. Cell toxicity tests showed that the UCNPs in phospholipid aqueous solution presented low cytotoxicity. Also, in vivo imaging and X-ray imaging revealed that the BiF₃:2%Er³⁺/20%Yb³⁺ NPs had deep penetration and high contrast, which meant it could be used as a potential probe and contrast agent in in vivo optical bioimaging.

Multifunctional BiF₃:Ln³⁺(Ln = Ho, Er, Tm)/Yb³⁺ UCLNPs presented better performances in dual-wavelength synergy, thermosensitivity, emission color tuning, and bioimaging.

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.

Controllable synthesis and luminescent properties of rare earth doped Gd2(MoO4)3 nanoplates

For the first time, we have successfully synthesized rare-earth doped Gd₂(MoO₄)₃: RE³⁺ (RE=Eu, Tb) nanoplates by solvothermal method. The morphology of Gd₂(MoO₄)₃ can be manipulated by changing the reaction times and reaction temperatures. The composition and surface morphology have been investigated by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), respectively. Under the excitation of UV, Photoluminescence (PL) has been used to explore the excellent luminescence properties of the synthesized nanophosphors. The Gd₂(MoO₄)₃: Eu³⁺ phosphors shows a hypersensitive red emission (612nm) when excitation wavelength within the scope of 200-350nm corresponding to a ⁵D₀-⁷F₂ transition. Similarly, the Gd₂(MoO₄)₃: Tb³⁺ phosphors certificate a highly strong green emission at 544nm at an excitation wavelength of 298nm corresponding to a ⁵D₄-⁷F₅ transition. Furthermore, the characteristic spectrum peak of the Gd₂(MoO₄)₃: Eu³⁺/Tb³⁺ nanophosphor exhibits the corresponding spectra position (green emission at 544nm and red emission at 612nm). Hence, the obtained Gd₂(MoO₄)₃: RE³⁺ nanoplates may establish highly potentiality in light field applications.

Efficient up-conversion in Yb:Er:NaT(XO4)2 thermal nanoprobes. Imaging of their distribution in a perfused mouse

Yb and Er codoped NaT(XO4)2 (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:β-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)2 and β-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT(XO4)2 oxides with large cutoff phonon energy (ħω≈ 920 cm-1) is ascribed to 4F9/2 electron population recycling to higher energy 4G11/2 level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)2 have been synthesized by sol-gel with sizes most commonly in the 50-80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.

Ultrasmall, water dispersible, TWEEN80 modified Yb:Er:NaGd(WO4)2 nanoparticles with record upconversion ratiometric thermal sensitivity and their internalization by mesenchymal stem cells

This work presents the synthesis by coprecipitation of diamond shaped Yb:Er:NaGd(WO₄)₂ crystalline nanoparticles (NPs) with diagonal dimensions in the 5-7 nm × 10-12 nm range which have been modified with TWEEN80 for their dispersion in water, and their interaction with mesenchymal stem cells (MSCs) proposed as cellular NP vehicles. These NPs belong to a large family of tetragonal Yb:Er:NaT(XO₄)₂ (T = Y, La, Gd, Lu; X = Mo, W) compounds with green (²H_11/2 + ⁴S_3/2 → ⁴I_15/2) Er-related upconversion (UC) efficiency comparable to that of Yb:Er:β-NaYF₄ reference compound, but with a ratiometric thermal sensitivity (S) 2.5-3.5 times larger than that of the fluoride. At the temperature range of interest for biomedical applications (∼293-317 K/20-44 °C) S = 108-118 × 10^-4 K^-1 for 20 at%Yb:5 at%Er:NaGd(WO₄)₂ NPs, being the largest values so far reported using the ²H_11/2/⁴S_3/2 Er intensity ratiometric method. Cultured MSCs, incubated with these water NP emulsions, internalize and accumulate the NPs enclosed in endosomes/lysosomes. Incubations with up to 10 μg of NPs per ml of culture medium maintain cellular metabolism at 72 h. A thermal assisted excitation path is discussed as responsible for the UC behavior of Yb:Er:NaT(XO₄)₂ compounds.

Hydrothermal synthesis, characterization and luminescence properties of CaGd2(MoO4)4:Eu3+ ovoid like structures

Red light emission from CaGd₂(MoO₄)₄:0.06Eu³⁺ phosphor by EDTA assisted hydrothermal route at 200 °C for 24 h.

A novel anion doping strategy to enhance upconversion luminescence in NaGd(MoO4)2:Yb3+/Er3+ nanophosphors

A novel and efficient F⁻ anion doping strategy is proposed for enhancing upconversion luminescence in NaGd(MoO₄)₂:Yb³⁺/Er³⁺ nanophosphors.