Structural, spectroscopic, and magnetic properties of Eu3+-doped GdVO4 nanocrystals synthesized by a hydrothermal method

Luminescent materials with dual-mode excitation and tunable emission color for anti-counterfeiting applications

GdVO₄-based dual-mode phosphors were successfully synthesized via a hydrothermal approach. The X-ray diffraction analysis determined the tetragonal structure as well as I4₁/amd space group of products by comparing with a reference pattern no. ICDD #01-072-0277. The morphology of yielded phosphors was confirmed by transmission electron microscopy and scanning electron microscopy. Detailed spectroscopy analysis revealed tunable luminescence properties with an increasing Yb³⁺ content in series of GdVO₄: x% Yb³⁺, y% Tm³⁺, 5% Eu³⁺ (x = 5, 10, 15, 20; y = 0.1, 0.5, 1) phosphors. For Yb³⁺, Tm³⁺, and Eu³⁺- codoped phosphors we observed bands related to the ¹G₄ → ³H₆ and ¹G₄ → ³F₄ transitions of Tm³⁺ ions, occurred through the cooperative up-conversion mechanism, where two nearby Yb³⁺ ions were involved in near-infrared absorption. Moreover, the GdVO₄: 20% Yb³⁺, 0.5% Tm³⁺, 5% Eu³⁺ showed the most outstanding color tunability from red color (x = 0.6338, y = 0.3172) under UV to blue color (x = 0.2640, y = 0.1988) under NIR excitation, which can be applied in anti-counterfeiting activity.

Effect of Cr3+ doping on structural and optical properties of Eu3+ doped LaVO4 phosphor

In this work, the Eu³⁺, Cr³⁺ doped and co-doped LaVO₄ phosphors have been prepared through a high temperature solid-state reaction method. The powder XRD patterns of phosphors are very sharp and intense, which reflects a highly crystalline nature of phosphors. The XRD data were also refined by a Rietveld refinement method. The particle size of the phosphor samples lies in the sub-micron to micron range. The existence of La, Eu, Cr, V and O elements was verified by EDS spectra. The FTIR spectra show various absorption bands due to different vibrating groups. The optical band gap of the phosphor decreases on increasing concentration of Cr³⁺ ion. The photoluminescence excitation spectra of Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor exhibit bands due to Eu³⁺ and Cr³⁺ ions. The Eu³⁺ doped LaVO₄ phosphor exciting at 393 and 316 nm wavelengths gives intense red color at 614 nm due to the ⁵D₀ → ⁷F₂ transition of the Eu³⁺ ion. When the Cr³⁺ ion is co-doped in the Eu³⁺ doped LaVO₄ phosphor the emission spectra contain emission bands due to Eu³⁺ and Cr³⁺ ions. The emission intensity of Eu³⁺ doped phosphor reduces due to energy transfer from Eu³⁺ to Cr³⁺ ions in presence of Cr³⁺ ions upon 393 and 386 nm excitations. The lifetime of the ⁵D₀ level of Eu³⁺ ions decreases in the Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor, which also reflects the energy transfer. The Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor also produces a large amount of heat upon 980 nm excitation. Thus, the Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphors may be used for LEDs, solid state lighting and heat generating devices.

Highly Sensitive Lanthanide-Doped Nanoparticles-Based Point-of-Care Diagnosis of Human Cardiac Troponin I

Introduction

Methods

Results

Conclusion

Influence of GdVO4:Eu3+ Nanocrystals on Growth, Germination, Root Cell Viability and Oxidative Stress of Wheat (Triticum aestivum L.) Seedlings

The increasing application of lanthanide-doped nanocrystals (LDNCs) entails the risk of a harmful impact on the natural environment. Therefore, in the presented study the influence of gadolinium orthovanadates doped with Eu³⁺ (GdVO₄:Eu³) nanocrystals on wheat (Triticum aestivum L.), chosen as a model plant species, was investigated. The seeds were grown in Petri dishes filled with colloids of LDNCs at the concentrations of 0, 10, 50 and 100 µg/mL. The plants’ growth endpoints (number of roots, roots length, roots mass, hypocotyl length and hypocotyl mass) and germination rate were not significantly changed after the exposure to GdVO₄:Eu³⁺ nanocrystals at all used concentrations. The presence of LDNCs also had no effect on oxidative stress intensity, which was determined on the basis of the amount of lipid peroxidation product (thiobarbituric acid reactive substances; TBARS) in the roots. Similarly, TTC (tetrazolium chloride) assay did not show any differences in cells’ viability. However, root cells of the treated seedlings contained less Evans Blue (EB) when compared to the control. The obtained results, on the one hand, suggest that GdVO₄:Eu³⁺ nanocrystals are safe for plants in the tested concentrations, while on the other hand they indicate that LDNCs may interfere with the functioning of the root cell membrane.

Vanadium-based nanomaterials for cancer diagnosis and treatment

In the past few decades, various vanadium compounds have displayed potential in cancer treatment. However, fast clearness in the body and possible toxicity of vanadium compounds has hindered their further development. Vanadium-based nanomaterials not only overcome these limitations, but take advantage of the internal properties of vanadium in photics and magnetics, which enable them as a multimodal platform for cancer diagnosis and treatment. In this paper, we first introduced the basic biological and pharmacological functions of vanadium compounds in treating cancer. Then, the synthesis routes of three vanadium-based nanomaterials were discussed, including vanadium oxides, 2D vanadium sulfides, carbides and nitrides: V_mX_n (X = S, C, N) and water-insoluble vanadium salts. Finally, we highlighted the applications of these vanadium-based nanomaterials as tumor therapeutic and diagnostic agents.

Influence of Bi3+ ion on structural, optical, dielectric and magnetic properties of Eu3+ doped LaVO4 phosphor

In this paper, we have studied the structural, optical, dielectric and magnetic properties of Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphors prepared by solid state reaction method. Rietveld structural analysis of the samples confirms the monoclinic crystal structure with P2₁/n space group. The particles size of Eu³⁺ doped LaVO₄ phosphor increased in presence of Bi³⁺ ion. The excitation spectrum of Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphor reveals bands due to charge transfer state (CTS) and electronic transitions of Eu³⁺ and Bi³⁺ ions. The Eu³⁺ doped LaVO₄ phosphor gives intense red emission centred at 613 nm due to ⁵D₀ → ⁷F₂ transition of Eu³⁺ ion excited at 266, 355 and 394 nm wavelengths. When Bi³⁺ and Eu³⁺ ions are co-doped in the LaVO₄ phosphor the photoluminescence intensity is enhanced upto two times. The photoluminescence intensity is largest for the 266 nm excitation. This is due to energy transfer from CTS and (¹P₁, ³P₁) levels of the Bi³⁺ ion to ⁵D₄ level of the Eu³⁺ ion and increase in the particles size of phosphor. The Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphors also show excellent dielectric and magnetic properties with a variation in frequency and magnetic field, respectively. Thus, the Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphor may be useful in fabricating displays devices, red emitting phosphors, dielectric capacitors and magnetic devices.

Morphology of the GdVO4 crystal: first-principles studies

The present paper reports a theoretical investigation based on first-principles density functional theory calculations to predict the external morphology of the tetragonal GdVO₄ crystal from its internal structure. The Bravais-Friedel-Donnay-Harker (BFDH) method, attachment energy (AE) method and surface energy (SE) method were used in this study. Slice energies (cohesive, attachment and specific surface) of the three main crystal faces having (110), (101) and (200) orientation and their d_hkl thicknesses were computed using CRYSTAL17 code, in the frame of a 2D periodic slab model. The relative growth rate (R_hkl) and the morphological importance (MI_hkl) for each unrelaxed and relaxed (hkl) face of interest were determined. Consequently, the crystal shapes predicted based upon BFDH, AE and SE methods were represented by the Wulff construction. The results of the morphology crystal predictions, based on the above methods, were compared both against each other and against the experimentally observed morphologies. A quite satisfactory agreement between the predicted and observed crystal morphologies is noticed.

GdVO4:Eu3+,Bi3+ Nanoparticles as a Contrast Agent for MRI and Luminescence Bioimaging

With the development of multifunctional imaging, gadolinium (Gd)-bearing inorganic nanoparticles (NPs), which were doped with trivalent lanthanide (Ln3+), have been applied in magnetic resonance imaging (MRI) and optical imaging owing to their high payload of Gd3+ ions and specific optical characteristics. In this study, we chose GdVO4 codoped with Eu3+ and Bi3+ as the host material to generate a highly efficient contrast agent (CA) for MRI and long-term luminescence imaging. The new CA emits strong and stable luminescence because of its strong characteristic emissions, resulting from the energy-transfer process from the vanadate groups (VO4 3-) to the Eu3+ and Bi3+ dopants. Additionally, these NPs provided conspicuous T 1 and T 2 relaxation time-shortening characteristics, which result in MRI enhancement. GdVO4:Eu3+,Bi3+ NPs were tested on liver tumor-bearing nude mice, and showed improved liver tumor contrast in T 2-weighted MR images (T 2WI). The dual-modal imaging probe exhibited no cytotoxicity or organ toxicity, reflecting its excellent biocompatibility. Thus, GdVO4:Eu3+,Bi3+ has the potential to be used for bioassays in vitro and liver tumor targeting in vivo. The results reveal the great promise of using the designed GdVO4:Eu3+,Bi3+ NPs as luminescent and MRI dual-mode bioprobes for clinical bioimaging applications.

K3Eu5(PO4)6: hydrothermal synthesis, crystal structure and photoluminescence properties

An anhydrous orthophosphate, K₃Eu₅(PO₄)₆ (tripotassium pentaeuropium hexaphosphate), has been prepared by a high-temperature solid-state reaction combined with hydrothermal synthesis, and its crystal structure was determined by single-crystal X-ray diffraction analysis (SC-XRD). The results show that the compound crystallizes in the monoclinic space group C2/c and the structure features a three-dimensional framework of [Eu₅(PO₄)₆]_∞, with the tunnel filled by K⁺ ions. The IR spectrum, UV-Vis spectrum and luminescence properties of polycrystalline samples of K₃Eu₅(PO₄)₆, annealed at temperatures of 650, 700, 750, 800 and 850 °C, were investigated. Although with a full Eu³⁺ concentration (9.96 × 10²¹ ions cm^-3), the self-activated phosphor K₃Eu₅(PO₄)₆ shows s strong luminescence emission intensity with a quantum yield of 37%. Under near-UV light excitation (393 nm), the series of samples shows the characteristic emissions of Eu³⁺ ions in the visible region from 575 to 715 nm. The sample sintered at 800 °C gives the strongest emission and its lifetime sintered at 800 °C (1.88 ms) is also the longest of all.

Tamm Plasmons Directionally Enhance Rare-Earth Nanophosphor Emission

Rare-earth-based phosphors are the materials on which current solid-state lighting technology is built. However, their large crystal size impedes the tuning, optimization, or manipulation of emitted light that can be achieved by their integration in nanophotonic architectures. Herein we demonstrate a hybrid plasmonic-photonic architecture capable of both channeling in a specific direction and enhancing by eight times the emission radiated by a macroscopically wide layer of nanophosphors. In order to do so, a slab of rare-earth-based nanocrystals is inserted between a dielectric multilayer and a metal film, following a rational design that optimizes the coupling of nanophosphor emission to collective modes sustained by the metal-dielectric system. Our approach is advantageous for the optimization of solid-state lighting systems.

Shape-controllable synthesis of GdVO4 photocatalysts and their tunable properties in photocatalytic hydrogen generation

Novel visible light responsive materials for water splitting are essential for the efficient conversion of solar energy into hydrogen bond energy. Among other semiconductors, gadolinium orthovanadate has appropriate conduction and valence band edges positioned to split water molecules and a narrow band gap that allows the use of visible light for hydrogen generation. Thus, we present here that hydrogen evolution under visible light (λ > 420 nm) could be accomplished using hierarchical 3D GdVO₄ particles, obtained by a simple, one pot hydrothermal synthesis. We found that applying various reaction components, such as EDTA-Na₂ and EDTA, and adjusting the pH of the solution allow one to tune the shape of GdVO₄ (such as short nanowires, long nanowires, short nanorods, long nanorods, nanoparticles and spheres - all having a tetragonal crystal structure) as well as optical and photocatalytic properties. The highest ability to photocatalytically split methanol solution into hydrogen under UV-Vis irradiation was detected for the long nanowire sample (42 μmol h^-1), having almost 11 times higher efficiency in comparison with the weakest sample - short nanowires. In addition, GdVO₄ spheres generated H₂ more than 2 times (5.75 μmol h^-1) in comparison with the short nanorod sample (2.5 μmol h^-1) under visible light excitation. Photostable in three-hour work cycles, long nanowires and spheres were even able to generate hydrogen from pure water, reaching values of 17 and 3 μmol under UV-Vis and Vis light, respectively.

Photonic structuring improves the colour purity of rare-earth nanophosphors

Nanophosphor integration in an optical cavity allows unprecedented control over both the chromaticity and the directionality of the emitted light, without modifying the chemical composition of the emitters or compromising their efficiency. Our approach opens a route towards the development of nanoscale photonics based solid state lighting.

Tunable and ultra-stable UV light-switchable fluorescent composites for information hiding and storage

Different information could be hidden and read under 365 nm and 254 nm light excitation, respectively. Moreover, the hidden information still can be identified after being exposed to an ambient environment for as long as 90 days.

Multifunctional GdVO4:Eu core–shell nanoparticles containing 225Ac for targeted alpha therapy and molecular imaging

Development of actinium-225 doped Gd_0.8Eu_0.2VO₄ core–shell nanoparticles as multifunctional platforms for multimodal molecular imaging and targeted radionuclide therapy.

Origin of the temperature-induced redshift of the charge transfer band of GdVO4

The charge transfer band (CTB) of the VO43- groups in vanadates shifts to longer wavelengths with increasing temperature. The origin of this temperature-induced redshift was explored by studying the temperature-dependent excitation and emission spectra of GdVO₄ ranging from 300 to 480 K. The influences of the thermal population and the decline of the charge transfer gap on the spectral shift were analyzed using the configurational coordinate diagram. We conclude that the thermal population of vibrational sublevels of the ground electronic energy level dominates the temperature-induced redshift of the CTB. Taking advantage of the redshift and the thermal quenching, a novel ratiometric temperature-sensing strategy was proposed. Drastic temperature dependence was achieved, indicating a promising candidate for an optical thermometer with high sensing performance.

Unclonable Security Codes Designed from Multicolor Luminescent Lanthanide-Doped Y2O3 Nanorods for Anticounterfeiting

The duplicity of important documents has emerged as a serious problem worldwide. Therefore, many efforts have been devoted to developing easy and fast anticounterfeiting techniques with multicolor emission. Herein, we report the synthesis of multicolor luminescent lanthanide-doped Y₂O₃ nanorods by hydrothermal method and their usability in designing of unclonable security codes for anticounterfeiting applications. The spectroscopic features of nanorods are probed by photoluminescence spectroscopy. The Y₂O₃:Eu³⁺, Y₂O₃:Tb³⁺, and Y₂O₃:Ce³⁺ nanorods emit hypersensitive red (at 611 nm), strong green (at 541 nm), and bright blue (at 438 nm) emissions at 254, 305, and 381 nm, respectively. The SEM and TEM/HRTEM results reveal that these nanorods have diameter and length in the range of 80-120 nm and ∼2-5 μm, respectively. The two-dimensional spatially resolved photoluminescence intensity distribution in nanorods is also investigated by using confocal photoluminescence microscopic technique. Further, highly luminescent unclonable security codes are printed by a simple screen printing technique using luminescent ink fabricated from admixing of lanthanide doped multicolor nanorods in PVC medium. The prospective use of these multicolor luminescent nanorods provide a new opportunity for easily printable, highly stable, and unclonable multicolor luminescent security codes for anti-counterfeiting applications.

Spectroscopic, structural and in vitro cytotoxicity evaluation of luminescent, lanthanide doped core@shell nanomaterials GdVO4:Eu(3+)5%@SiO2@NH2

The luminescent GdVO4:Eu(3+)5%@SiO2@NH2 core@shell nanomaterials were obtained via co-precipitation method, followed by hydrolysis and co-condensation of silane derivatives: tetraethyl orthosilicate and 3-aminopropyltriethoxysilane. Their effect on human erythrocytes sedimentation and on proliferation of human lung microvascular endothelial cells was examined and discussed. The luminescent nanoparticles were synthesized in the presence of polyacrylic acid or glycerin in order to minimalize the agglomeration and excessive growth of nanostructures. Surface coating with amine functionalized silica shell improved their biocompatibility, facilitated further organic conjugation and protected the internal core. Magnetic measurements revealed an enhanced T1-relaxivity for the synthesized GdVO4:Eu(3+)5% nanostructures. Structure, morphology and average grain size of the obtained nanomaterials were determined by X-ray diffraction, transmission electron microscopy and dynamic light scattering analysis. The qualitative elemental composition of the nanomaterials was established using energy-dispersive X-ray spectroscopy. The spectroscopic characteristic of red emitting core@shell nanophosphors was completed by measuring luminescence spectra and decays. The emission spectra revealed characteristic bands of Eu(3+) ions related to the transitions (5)D0-(7)F0,1,2,3,4 and (5)D1-(7)F1. The luminescence lifetimes consisted of two components, associated with the presence of Eu(3+) ions located at the surface of the crystallites and in the bulk.

Tunable photoluminescence and magnetic properties of Dy(3+) and Eu(3+) doped GdVO4 multifunctional phosphors

A series of Dy(3+) or/and Eu(3+) doped GdVO4 phosphors were successfully prepared by a simple hydrothermal method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectrometry (EDS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). The results indicate that the as-prepared samples are pure tetragonal phase GdVO4, taking on nanoparticles with an average size of 45 nm. Under ultraviolet (UV) light excitation, the individual Dy(3+) or Eu(3+) ion activated GdVO4 phosphors exhibit excellent emission properties in their respective regions. The mechanism of energy transfer from the VO4(3-) group and the charge transfer band (CTB) to Dy(3+) and Eu(3+) ions is proposed. Color-tunable emissions in GdVO4:Dy(3+),Eu(3+) phosphors are realized through adopting different excitation wavelengths or adjusting the appropriate concentration of Dy(3+) and Eu(3+) when excited by a single excitation wavelength. In addition, the as-prepared samples show paramagnetic properties at room temperature. This kind of multifunctional color-tunable phosphor has great potential applications in the fields of photoelectronic devices and biomedical sciences.

Reddish-orange-emitting and paramagnetic properties of GdVO4:Sm3+/Eu3+ multifunctional nanomaterials

The as-prepared samples are short and rod-like in shape with a diameter of about 10 nm and length of about 20–30 nm. The excitation spectra indicate that Sm³⁺ ions transfer energy to Eu³⁺ ions, which increases the color purity of Eu³⁺ ions in the GdVO₄ system.

Cubic KLu3F10 nanocrystals: Mn2+ dopant-controlled synthesis and upconversion luminescence

Rare-earth-doped cubic KLu₃F₁₀ nanocrystals with excellent upconversion luminescence have been fabricated by adding Mn²⁺ ions.