Urea-based Homogeneous Precipitation Research Articles

Controllable synthesis of bifunctional monodisperse gadolinium orthosilicate core-shell nanospheres

Rare-earth scintillator particles with uniform size have garnered significant attention in the biomedical field. In this study, monodisperse spheres of Gd2SiO5:Ce3+@SiO2 (GSO:Ce3+@SiO2) were synthesized via urea-based homogeneous precipitation and the Stöber method. Firstly, the growth process of the precursor spheres was studied by adjusting reaction conditions, including reaction temperature, reaction time, pH, RE3+ ions and urea concentration. Secondly, the evolution of the core-shell structure of the precursor spheres following TEOS coating and calcination was discussed. Core-shell monodisperse spheres with a particle size of approximately 170 nm were obtained. Thirdly, the luminescence characteristics of GSO:Ce3+@SiO2 was investigated under UV and X-ray excitation, and the effects of varying the thickness of the SiO2 shell layer on the fluorescence properties of GSO:Ce3+@SiO2 were discussed. The study revealed that the obtained GSO:Ce3+@SiO2 exhibited excellent stability characteristics, blood compatibility and displayed a favorable spectral match with porphyrin-based photosensitizers in the blue-light region. The present work provides a promising nanomaterial with potential applications in biomedical fields, including X-ray photodynamic therapy and magnetic resonance imaging.

The synthesis and luminescence properties of Bi3+/Eu3+ co-doped Gd2O3 phosphors with high thermal stability and tunable emission via energy transfer

In this work, the highly monodisperse (Gd0.99-xBi0.01Eux)2O3 phosphors with spherical morphologies (∼170 nm) are successfully obtained through precursor synthesis via urea-based homogeneous precipitation (UBHP) method, followed by annealing at 1000 °C. The Bi/Eu-doped does not alter the crystal structure, and maintain the cubic structure of the Gd2O3 host. Owing to the Bi3+ occupies two different sites (C2, S6) in Gd2O3 of the cubic phase, the 1S0 → 3P1 transition of Bi3+ has two significant excitation bands (335 nm and 375 nm). By monitoring the excitation at 335 nm and 375 nm, the (Gd0.99-xBi0.01Eux)2O3 phosphors show both Bi3+ (420 nm and 530 nm) and Eu3+ (611 nm) emissions, respectively. The presences of Gd3+ and Bi3+ excitation bands on the PLE spectra by monitoring the Eu3+ emission indicate the Bi3+ → Eu3+ and Gd3+ → Eu3+ energy transfer, respectively, and the energy transfer efficiency is up to 99 %. Meanwhile, the energy transfer mechanism of the (Gd0.99-xBi0.01Eux)2O3 samples is dominated by the dipole-dipole interaction. Under two different excitation wavelengths, the emission intensity varies with the Eu3+ doping content and the quenching concentration is about 3 at%. The calculated value of the critical distance Rc is 12.12 Å, which indicates that the quenching mechanism is mainly caused by the multipole interaction. Meanwhile, the emission color can be tuned though adjusting the Eu3+ content. The temperature-dependent (in the range of 100–500 K) analysis has been obtained, the results indicate the (Gd0.99-xBi0.01Eux)2O3 samples have good thermal stability. The (Gd0.99-xBi0.01Eux)2O3 phosphors developed in this work is expected to be widely used in lighting and optical display applications.

Facile fabrication of monodispersed α- and γ-Al2O3 microspheres through controlled calcination of alumina precursors synthesized by homogeneous precipitation

Monodispersed spherical particles of γ- and α-alumina were synthesized by urea-based homogeneous precipitation, using potassium sulfate and aluminum nitrate as the precursor and urea as a precipitating agent. The influence of various synthesis parameters like concentration of reactants, temperature, and reaction time, on the morphological features of alumina were investigated. Results showed that all the experimental parameters had a considerable effect on the morphology of the synthesized alumina, and control of these parameters resulted in monodispersed spherical particles with good dispensability and filtering performance. Extensive optimization of the experimental parameters led to produced alumina precursors with spherical morphology and an average particle size of 610 nm. The precipitated solids were characterized by various techniques and it was noted that the as-prepared particles were amorphous. Relatively well-dispersed and crystalline γ- and α-Al2O3 with higher sintering activity were obtained by calcining the as-synthesized precursors at 1000 and 1200 °C, respectively. The crystallographic results showed that crystallite size increased with an increase in annealing temperature. It was observed that the crystallite size of γ-Al2O3 was much smaller (5.71 nm ± 7.21%) than α-Al2O3 (35.40 nm) ± 4.58%. The Scanning electron microscopic analysis of the calcined alumina showed that the particle morphology was retained to a greater extent after calcination. The synthesized alumina particles can be used as a reinforcement filler in the Ni/Al2O3 composite coatings to enhance the tribological and mechanical properties of Ni-composite coating on a steel surface. The incorporated alumina particles in the composite may improve the properties of the coatings.

A facile homogeneous precipitation route synthesis of LiNi1/3Co1/3Mn1/3O2 cathode material for lithium-ion batteries

LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode material has widen prospects due to its high thermal stability, long battery life and high safety. However, the electrochemical performance of NCM111 is affected by particle distribution microstructure. In this paper, NCM111 cathode material is prepared by urea-based homogeneous precipitation method. The obtained NCM111 has small particle and well distributed, which has good electrochemical performance. The as-synthesized NCM111 cathode material exhibits a good initial discharge specific capacity of 205 mAh/g at 0.2 C. The study manifested that homogeneous precipitation method is a simple way to prepare high property NCM111 cathode material.

Phosphate source induced rapid synthesis of urchin-like hydrated GdPO4:Eu3+ nanoparticles: Imaging and drug delivery in A549 cell line

Energy and environmental concerns are increasing owing to the increased consumption of resources. To help solve the energy crisis and contribute to protecting our environment, this study aimed to develop a fast and eco-friendly method of synthesis. We propose a H3PO4 assisted fast synthesis technique for developing urchin-like GdPO4·xH2O:5Eu3+ nanoparticles. First, Gd(OH)CO3:5Eu3+ nanospheres with sizes of about 60 nm were developed using urea-based homogeneous precipitation. These nanospheres were utilized as the Gd3+ source and sacrificial templates in the formation of urchin-like GdPO4.xH2O:5Eu3+ nanoparticles, where the Kirkendall effect takes place during hydrothermal synthesis. The structural properties confirmed the existence of the H2O phase in the GdPO4:5Eu3+ nanoparticles. The synthesized urchin-like GdPO4·xH2O:5Eu3+ nanoparticles exhibited excellent photoluminescence in the reddish-orange region upon excitation by near-UV excitation wavelengths. These urchin-like nanoparticles demonstrated effective penetration in lung cancer cells by exhibiting luminescence from both the cytoplasm and nucleoplasm. The conjugation of doxorubicin with urchin-like GdPO4·xH2O:5Eu3+ nanoparticles helped to realize efficient antitumor activity against lung cancer.

Controllable synthesis and luminescence properties of NaYF4@YOF composite microcrystals with multiform morphologies

A variety of α-NaYF4@YOF composites with diverse morphologies and particles sizes have been fabricated via an easy-to-operate approach. First of all, the YB(OH)4CO3 precursor was obtained by a urea-based homogeneous precipitation route. Subsequently, the uniform and well-dispersed β-NaYF4 microcrystals with a variety of crystal shapes were synthesized by a simple hydrothermal process. The morphology and particle size of the β-NaYF4 samples can be adjusted in a controlled manner by simply tuning the reaction temperature and time, feeding molar ratio of precursor/NaF, or total amount of the reactants. Finally, the β-NaYF4 microcrystals converted to α-NaYF4@YOF composites which inherited the morphology and dispersity of the hydrothermal products after an annealing process in air. Upon UV or NIR excitation, the as-synthesized lanthanide ions Ln3+ (Eu3+, Tb3+, Yb3+/Er3+, Yb3+/Ho3+) doped α-NaYF4@YOF samples show the intense characteristic down-conversion (DC) or up-conversion (UC) multicolor emissions. Moreover, the calcination process not only broadens the excitation range but also improves the emission efficiency of the phosphors due to the enhanced crystallintiy and formation of YOF shell. The as-synthesized Ln3+-doped luminescent materials may find potential applications in fields of color displays, optoelectronic devices, and light-emitting diodes (LEDs).

The position shifting of charge transfer band in Eu3+-doped Re2O3 phosphors

A series of Eu3+ ion doped Re2O3 (Re = Sc, Lu, Y, Gd, La) phosphors have been synthesized via a simple urea-based homogeneous precipitation route. The position shifting of Eu3+ - O2– charge transfer (CT) band from the ligands O2– to the central ion Eu3+ and the 5D0 → 7F2 red luminescence of Eu3+ ion in Eu3+-doped Re2O3 phosphors has been investigated. In addition, the morphologies of Eu3+-doped Sc2O3, Ln2O3 (Lu2O3, Y2O3, Gd2O3) and La2O3 phosphors are irregular-shaped, approximate spherical and spindle-shaped, respectively. Our work provides a reference for the Eu3+-doped other oxide.

Controllable synthesis and luminescence property of spherical Lu(OH)CO3:Ln3+/LuBO3:Ln3+ (Ln = Eu, Tb) nanoparticles

Lu(OH)CO3:Ln3+/LuBO3:Ln3+ (Ln = Eu, Tb) nanospheres have been synthesized by the soft chemistry route. This synthesis process does not require the addition of any organic solvents and surfactant. The whole process consists of homogeneous precipitation and hydrothermal process. First, uniform spherical Lu(OH)CO3:Ln3+ (Ln = Eu, Tb) nanoparticles with the sizes of 70 nm were obtained by the classic urea-based homogeneous precipitation. Then, with the above Lu(OH)CO3:Ln3+ (Ln = Eu, Tb) nanosphere as the precursor, the composites of Lu(OH)CO3:Ln3+/LuBO3:Ln3+ (Ln = Eu, Tb) nanospheres formed by the simple hydrothermal process. The phases, morphologies, as well as the luminescence properties of as-prepared samples were characterized by means of X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and photoluminescence. Under a short wavelength excitation, the down-conversion Eu3+ and Tb3+-doped LuBO3 samples were investigated and explained.

Controlling the morphology and size of (Gd0.98−xTb0.02Eu x )2O3 phosphors presenting tunable emission: formation process and luminescent properties

The (Gd0.98−xTb0.02Eu x )2O3 phosphors have been successfully obtained using the urea-based homogeneous precipitation method in the present work. The particle growth of the precursors with mono-dispersion spherical morphology is surface-diffusion controlled and precipitated in the order of the Tb(OH)CO3 > Gd(OH)CO3 > Eu(OH)CO3, and the formation process has been also studied in detail. Partially replacing the pure water with ethylene glycol (EG) can control the particle size and morphology owing to its lower permittivity constant and interface energy. By monitoring the excitation at 314 nm (4f8 → 4f75d1 transition of Tb3+), the (Gd0.98−xTb0.02Eu x )2O3 phosphors exhibit both Tb3+ (green) and Eu3+ (red) emissions at 547 and 613 nm, respectively. The presence of Gd3+ and Tb3+ excitation bands on the PLE spectra by monitoring the Eu3+ emission directly provides an evidence of the Tb3+ → Eu3+ and Gd3+ → Eu3+ energy transfer, respectively. The quenching concentration is determined to be 2.0 at.%, and the quenching mechanism is determined to be the exchange reaction between Eu3+. The emission color can be readily tuned from approximately green to red via adjusting the Eu3+ content. The temperature-dependent analysis has been performed, and the results indicate that the (Gd0.98−xTb0.02Eu x )2O3 samples possess good thermal stability. Owing to the Tb3+ → Eu3+ energy transfer, the lifetime for the Tb3+ emission rapidly decreases, and the energy transfer efficiency has been calculated. The EG addition does not bring appreciable changes to the lifetime values for the both Tb3+ and Eu3+ emissions, but enhances remarkably the luminescent intensity which confirms the variation of the particle morphology/size, and the reason can be explained by the scattering of the light. The (Gd0.98−xTb0.02Eu x )2O3 phosphors developed in this work hopefully meet the requirements of various lighting and optical display applications.

A Green Route to Synthesize Pr3+/Dy3+-Doped Nd2O3 Nanoreplicas from Nd–Fe–B Magnets

This paper details a green and sustainable process for synthesizing highly concentrated Pr3+/Dy3+-doped Nd2O3 nanoparticles from Nd–Fe–B magnets sourced from e-waste via a facile homogeneous precipitation route under mild conditions. Rare earth elements (REEs) are under a serious crisis owing to their uncertain supply and increasing global demand. REEs’ future demand growth is mainly linked to the use of Nd–Fe–B magnets, which are currently one of the most widely used types of rare-earth magnets with extensive implementation in a variety of applications. Using REEs (i.e., Nd, Pr, and Dy) derived from Nd–Fe–B magnets, we applied a low temperature urea-based homogeneous precipitation method and synthesized crystallized RE (i.e., Nd, Pr, and Dy) OHCO3 nanoparticles with diameters of 40–50 nm and high specific surface area of 60 m2 g–1. The synthesized REOHCO3 was used as a precursor for the synthesis of REO nanoparticles through a thermal degradation process at 700 °C. FE-SEM images revealed that the synthes...

Local symmetry distortion-induced enhancement of upconversion luminescence in Gd2O3:Ho3+/Yb3+/Zn2+ nanoparticles for solid-state lighting and bioimaging

The Ho3+/Yb3+/Zn2+-tridoped Gd2O3 nanoparticles were prepared by a simple urea-based homogeneous precipitation method. Under near-infrared (NIR) light excitation, all the synthesized nanoparticles exhibit bright green and red upconversion (UC) emissions corresponding to the intra-4f transitions of Ho3+ ions and the UC mechanism is found to be a two-photon process. With the introduction of Zn2+ ions, not only the local symmetry surrounding the dopants is decreased, but also the UC emission intensity is also enhanced, which is further verified by the Judd-Ofelt theory. The temperature-dependent UC emission spectra were recorded to examine the thermal stability of the final products. From theoretical calculations, the activation energy is found to be about 0.18 eV. A novel green light-emitting diode device, which consists of the resultant nanoparticles and a NIR chip, was fabricated to examine their suitability for solid-state lighting. Meanwhile, the synthesized nanoparticles exhibit low cytotoxicity in various cell lines, suggesting their potential applications in in vivo UC luminescence imaging. Additionally, the applicability of the Ho3+/Yb3+/Zn2+-tridoped Gd2O3 nanoparticles for in vivo bioimaging applications was also analyzed.

Morphology/size effect on the luminescence properties of the [(YxGd1-x)0.98Dy0.02]2O3 phosphor with enhanced yellow emission

The [(Y0.05Gd0.95)0.98Dy0.02]2O3 phosphor with different particle size and morphology was obtained through precursor synthesis via urea-based homogeneous precipitation (UBHP) method, followed by annealing. The synthesis, particle morphology/size control, luminescent properties and energy transfer of the [(Y0.05Gd0.95)0.98Dy0.02]2O3 phosphor were systematically studied by the combined techniques of XRD, FE-SEM, FT-IR, PLE/PL spectroscopy, fluorescence decay and quantum efficiency analysis. Partly replacing water with ethylene glycol (EG) addition as solvent, the precursor morphology gradually changed from sphere to flower, and the size of sphere decreased with the ethylene glycol addition. The pure [(Y0.05Gd0.95)0.98Dy0.02]2O3 oxide remains the precursor morphology even at the high temperature of 1000°C. The phosphors all exhibit strong yellow emission band at ~574nm (4F9/2→6H13/2 transitions of Dy3+) under optimal UV excitation into the 8S7/2→6IJ intra f-f transition of Gd3+ at ~276nm indicating the efficient Gd3+→Dy3+ energy transfer. The Gd3+→Dy3+ energy transfer efficiency gradually decreases with the Y3+ concentration increasing. The particle morphology/size does not alter the fluorescence lifetime (~0.69 ± 0.04ms), color coordinate (~0.45, ~0.48), temperature (~3200K) and color purity (~82.09%), but brings about appreciable change to the emission intensity and quantum efficiency, and the detailed effect mechanism was discussed in this work. The size/morphology controlled phosphor of [(Y0.05Gd0.95)0.98Dy0.02]2O3 with yellow-emitting is expected to be widely used in the lighting and display areas.

Facile synthesis of Gd_2O_3:Ho^3+/Yb^3+ nanoparticles: an efficient upconverting material for enhanced photovoltaic performance of dye-sensitized solar cells

A series of Ho3+/Yb3+-codoped Gd2O3 nanoparticles were prepared by a facile urea-based homogeneous precipitation method. Under the excitation of 980 nm light, all the samples exhibited strong green and red upconversion (UC) emissions corresponding to the (5F4,5S2) → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions, respectively. A gradual enhancement in the UC emission intensity was observed with increasing the Yb3+ ion concentration, achieving its optimum value when the doping concentration was 3 mol%. In addition, with the introduction of Ho3+/Yb3+-codoped Gd2O3 nanoparticles into the TiO2 porous film of dye-sensitized solar cells (DSSCs), the power conversion efficiency of the cells (7.403%) was ~10.47% higher than that of the DSSCs with pure TiO2 porous film (6.701%), which is mainly caused by increased short-circuit current density due to their enhanced light-harvesting properties via an efficient UC process. The result suggested that the incorporation of upconverting nanoparticles into the TiO2 porous film is an effective approach to improve the photovoltaic characteristics of DSSCs.

Synthesis and characterizations of pompon-like Y2O2SO4:Eu3+ phosphors using a UBHP technique based on UAS system

The pompon-like Y2O2SO4:Eu3+ phosphors have been successfully synthesized using a urea-based homogeneous precipitation (UBHP) technique based on urea-ammonium sulfate (UAS) system. Detailed characterizations of the synthetic products were attained by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis and thermo-gravimetry (DTA – TG) and photoluminescence (PL) spectroscopy. SEM observations clearly revealed that morphologies of the synthetic products were controllable by m values, namely, the molar ratio of SO42− groups to Y3+ ions, and when m=5, pure pompon-like Y2O2SO4 phosphor with 2 – 3μm in diameter was obtained. FT-IR and XRD results showed this precursor was composed of amorphous yttrium hydroxyl, carbonate and sulfate groups compound and could be converted into pure Y2O2SO4 phase by calcined at 800°C for 2h in air. PL spectra of the Y2O2SO4:Eu3+ phosphors under 268nm ultraviolet (UV) light excitation showed a red emission at 620nm as the most prominent peak, which attributes to the 5D0→7F2 transition of Eu3+ ions. The quenching concentration of Eu3+ ions is 5mol%. The concentration quenching mechanism is the exchange interaction and its corresponding lifetime is 1.85ms according to the linear fitting result.

Enhanced Photovoltaic Performance of Dye-Sensitized Solar Cells by Efficient Near-Infrared Sunlight Harvesting using Upconverting Y2O 3:Er (3+)/Yb (3+) Phosphor Nanoparticles.

We report the efficiency enhancement in dye-sensitized solar cells (DSSCs) using Er3+/Yb3+-co-doped Y2O3 (i.e., Y2O3:Er3+/Yb3+) phosphor nanoparticles, prepared by a simple and cost-effective urea-based homogeneous precipitation method, for efficient near-infrared (NIR) sunlight harvesting. Under the light excitation at a wavelength of 980 nm, the as-prepared samples exhibited strong upconversion emissions at green and red visible wavelengths. To investigate the influence of Y2O3:Er3+/Yb3+ nanoparticles on the photovoltaic performance of DSSCs, the phosphor nanoparticles were incorporated into titanium dioxide films to form a composite photoelectrode. For the resulting DSSCs, the increased power conversion efficiency (PCE) of 6.68 % was obtained mainly by the increased photocurrent of JSC = 13.68 mA/cm2 due to the light harvesting enhancement via the NIR-to-visible upconversion process (cf., PCE = 5.94 %, JSC = 12.74 mA/cm2 for the reference DSSCs without phosphor nanoparticles), thus, indicating the PCE increment ratio of ~12.4 %.

Gas sensing properties of semiconducting copper oxide nanospheroids

Monosize spheroidal porous particles of copper oxide were produced by controlled calcination of the copper basic carbonate particles, synthesized by the urea-based homogeneous precipitation process. After characterization by various physical methods, such as SEM, XRD, and FTIR, the copper oxide particles were employed for the fabrication of the gas sensor. The latter was made up of a thick film of copper oxide on alumina plate, having printed interdigitated gold electrodes. Electrical properties of the sensor material were evaluated as a function of the temperature, which indicated its semiconductor behavior. On exposing to ammonia gas, the sensor responded in the form of a decrease in electrical resistance in a reproducible manner. Reproducibility in performance was attributed to the use of monodispersed particles of copper oxide in the fabrication of sensor.

Improved luminescence behavior of YVO4:Eu3+ hollow microspheres by Ca2+ doping

The YVO4:Eu3+/Ca2+ hollow microspheres were prepared via a urea-based homogeneous precipitation method in the presence of colloidal melamine formaldehyde resin (MF) microspheres as templates without heat treatment. Photoluminescence characteristics of YVO4:Eu3+ hollow microspheres are studied. X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) measurements were carried out to characterize their structural and luminescent properties. When compared with those of YVO4:Eu3+ hollow microsphere, the emissions of codoped sample with Ca2+ are greatly enhanced. The intensity of charge transfer absorption at 312nm and its red emission have been greatly increased by codoping the Ca2+ ion into the YVO4:Eu3+ lattice.

Fabrication of Lu2O3:Eu transparent ceramics using powder consisting of mono-dispersed spheres

Mono-dispersed spherical Lu2O3:Eu (5mol%) powders for transparent ceramics fabrication were synthesized by urea-based homogeneous precipitation technique. The effects of the doped-Eu3+ on the synthesis of Lu2O3:Eu particles were investigated in detail. The results show that the doping of Eu3+ ions into Lu system can significantly decrease the particle size of the resultant precursor spheres. Owing to the sequential precipitation in Lu/Eu system, there are compositional gradients within each of the resultant precursor spheres. Well dispersed, homogeneous and spherical/near spherical Lu2O3:Eu powders were obtained after calcination at 600–1000°C for 4h. The powder calcined at 600°C shows better sintering behavior and can be densified into transparent ceramic after vacuum sintering at 1700°C for 5h. The luminescence properties of the obtained Lu2O3:Eu powder and transparent ceramic were also studied.

Size-dependent Luminescence Behavior of (Y,Gd,Tb)2O3 Monodispersed Spherical Green Phosphors

(Y,Gd,Tb)2O3 monodispersed spheres have been calcined from the precursors synthesized via urea-based homogeneous precipitation. The resultant particles are polycrystalline, consisting of ∼40 nm grains. A facile particle size control from 162 nm to 110 nm can be achieved through varying the urea/cation molar ratio. Upon UV excitation at ∼275 nm, the phosphors exhibit green emission at ∼546 nm (5D4→7F5 transition of Tb3+). The phosphors showed luminescent intensity clearly dependent on their particle size, and stronger emission was found for larger spheres mainly due to their smaller surface area. However, the oxides with various particle sizes exhibited similar lifetimes of ∼1.51ms.

Host sensitized spherical up-conversion phosphor Yb2O3:Er3+

Host sensitized up-conversion phosphors Yb2O3:Er3+ with sphere-shaped morphology were prepared by a urea-based homogeneous precipitation process. The effects of sintering temperature on the structure and morphology of particles were investigated. The up-conversion emission spectra of Yb2O3:Er3+ with 980nm excitation exhibit the green and red double bands, attributing to 2H11/2/4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions, respectively. The possible up-conversion mechanism and processes were also proposed.