Tunable Luminescence of Sr₂CeO₄:M²⁺ (M = Ca, Mg, Ba, Zn) and Sr₂CeO₄:Ln³⁺ (Ln = Eu, Dy, Tm) Nanophosphors

Nanophosphors based on cerium–strontium oxide (Sr₂CeO₄), doped with M²⁺ or Ln³⁺ (M = Ca, Mg, Ba, Zn; Ln = Eu, Dy, Tm) were successfully prepared using a modified Pechini method. The structure of prepared materials has been confirmed and characterized using several techniques such as X-ray powder diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The obtained materials were composed of nanocrystals with an average size around ∼50 nm. The luminescence properties of synthesized nanophosphors were characterized by excitation or emission spectra and luminescence lifetimes. The chromaticity coordinates were also calculated to demonstrate changes of the luminescence color

Multifunctional Optical Sensors for Nanomanometry and Nanothermometry: High-Pressure and High-Temperature Upconversion Luminescence of Lanthanide-Doped PhosphatesLaPO₄/YPO₄:Yb³⁺–Tm³⁺

Upconversion luminescence of nano-sized Yb³⁺ and Tm³⁺ codoped rare earth phosphates, that is, LaPO₄ and YPO₄, has been investigated under high-pressure (HP, up to ∼25 GPa) and high-temperature (293–773 K) conditions. The pressure-dependent luminescence properties of the nanocrystals, that is, energy red shift of the band centroids, changes of the band ratios, shortening of upconversion lifetimes, and so forth, make the studied nanomaterials suitable for optical pressure sensing in nanomanometry. Furthermore, thanks to the large energy difference (∼1800 cm^–1), the thermalized states of Tm³⁺ ions are spectrally well-separated, providing high-temperature resolution, required in optical nanothermometry. The temperature of the system containing such active nanomaterials can be determined on the basis of the thermally induced changes of the Tm³⁺ band ratio (³F_2,3 → ³H₆/³H₄ → ³H₆), observed in the emission spectra. The advantage of such upconverting optical sensors is the use of near-infrared light, which is highly penetrable for many materials. The investigated nanomanometers/nanothermometers have been successfully applied, as a proof-of-concept of a novel bimodal optical gauge, for the determination of the temperature of the heated system (473 K), which was simultaneously compressed under HP (1.5 and 5 GPa)

Hydrothermal Synthesis and Structural and Spectroscopic Properties of the New Triclinic Form of GdBO₃:Eu³⁺ Nanocrystals

Triclinic Gd_1‑<i>x</i>Eu_<i>x</i>BO₃ nanophosphors have been prepared by a hydrothermal method without using additional coreagents and prior precipitation of precursor (<i>in situ</i>). The formation of the borate nanorods and their crystal structure was refined on the basis of X-ray diffraction patterns (XRD) and well confirmed using various techniques such as infrared spectroscopy (IR), Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The new triclinic crystal structure (space group <i>P</i>1̅) for the GdBO₃ nanocrystals and detailed structure parameters were determined with the help of the Rietveld analysis. The spectroscopic characteristics of the synthesized nanomaterials with different concentrations of Eu³⁺ ions were defined with the use of luminescence excitation spectra as well as emission spectra and decay kinetics. The Judd–Ofelt parameters (Ω₂, Ω₄) and quantum efficiency, η, were also calculated for the more detailed analysis of Eu³⁺ spectra in the GdBO₃ host

Hydrothermal Synthesis and Structural and Spectroscopic Properties of the New Triclinic Form of GdBO₃:Eu³⁺ Nanocrystals

Triclinic Gd_1‑<i>x</i>Eu_<i>x</i>BO₃ nanophosphors have been prepared by a hydrothermal method without using additional coreagents and prior precipitation of precursor (<i>in situ</i>). The formation of the borate nanorods and their crystal structure was refined on the basis of X-ray diffraction patterns (XRD) and well confirmed using various techniques such as infrared spectroscopy (IR), Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The new triclinic crystal structure (space group <i>P</i>1̅) for the GdBO₃ nanocrystals and detailed structure parameters were determined with the help of the Rietveld analysis. The spectroscopic characteristics of the synthesized nanomaterials with different concentrations of Eu³⁺ ions were defined with the use of luminescence excitation spectra as well as emission spectra and decay kinetics. The Judd–Ofelt parameters (Ω₂, Ω₄) and quantum efficiency, η, were also calculated for the more detailed analysis of Eu³⁺ spectra in the GdBO₃ host

Structural, Spectroscopic, and Magnetic Properties of Eu³⁺-Doped GdVO₄ Nanocrystals Synthesized by a Hydrothermal Method

New interesting aspects of the spectroscopic properties, magnetism, and method of synthesis of gadolinium orthovanadates doped with Eu³⁺ ions are discussed. Gd_1–<i>x</i>Eu_<i>x</i>VO₄ (<i>x</i> = 0, 0.05, 0.2) bifunctional luminescent materials with complex magnetic properties were synthesized by a microwave-assisted hydrothermal method. Products were formed in situ without previous precipitation. The crystal structures and morphologies of the obtained nanomaterials were analyzed by X-ray diffraction and transmission and scanning electron microscopy. Crystallographic data were analyzed using Rietveld refinement. The products obtained were nanocrystalline with average grain sizes of 70–80 nm. The qualitative and quantitative elemental composition as well as mapping of the nanocrystals was proved using energy-dispersive X-ray spectroscopy. The spectroscopic properties of red-emitting nanophosphors were characterized by their excitation and emission spectra and luminescence decays. Magnetic measurements were performed by means of vibrating sample magnetometry. GdVO₄ and Gd_0.8Eu_0.2VO₄ exhibited paramagnetic behavior with a weak influence of antiferromagnetic couplings between rare-earth ions. In the substituted sample, an additional magnetic contribution connected with the population of low-lying excited states of europium was observed

Structural, Spectroscopic, and Magnetic Properties of Eu³⁺-Doped GdVO₄ Nanocrystals Synthesized by a Hydrothermal Method

New interesting aspects of the spectroscopic properties, magnetism, and method of synthesis of gadolinium orthovanadates doped with Eu³⁺ ions are discussed. Gd_1–<i>x</i>Eu_<i>x</i>VO₄ (<i>x</i> = 0, 0.05, 0.2) bifunctional luminescent materials with complex magnetic properties were synthesized by a microwave-assisted hydrothermal method. Products were formed in situ without previous precipitation. The crystal structures and morphologies of the obtained nanomaterials were analyzed by X-ray diffraction and transmission and scanning electron microscopy. Crystallographic data were analyzed using Rietveld refinement. The products obtained were nanocrystalline with average grain sizes of 70–80 nm. The qualitative and quantitative elemental composition as well as mapping of the nanocrystals was proved using energy-dispersive X-ray spectroscopy. The spectroscopic properties of red-emitting nanophosphors were characterized by their excitation and emission spectra and luminescence decays. Magnetic measurements were performed by means of vibrating sample magnetometry. GdVO₄ and Gd_0.8Eu_0.2VO₄ exhibited paramagnetic behavior with a weak influence of antiferromagnetic couplings between rare-earth ions. In the substituted sample, an additional magnetic contribution connected with the population of low-lying excited states of europium was observed

Effects of Dopant Addition on Lattice and Luminescence Intensity Parameters of Eu(III)-Doped Lanthanum Orthovanadate

A series of La_1–<i>x</i>Eu_<i>x</i>VO₄ samples with a different Eu³⁺ content was synthesized via a hydrothermal route. An increase in the dopant content resulted in a decrease in lattice constants of the materials. Plane-wave DFT calculations with PBE functional in CASTEP confirmed this trend. Next, CASTEP calculations were used to obtain force constants of Eu–O bond stretching, using a novel approach which involved displacement of the Eu³⁺ ion. The force constants were then used to calculate charge donation factors <i>g</i> for each ligand atom. The chemical bond parameters and the geometries from DFT calculations were used to obtain theoretical Judd–Ofelt intensity parameters Ω_λ. The effects of geometry changes caused by the dopant addition were analyzed in terms of Ω_λ. The effects of distortions in interatomic angles of the Eu³⁺ coordination geometry on the Ω_λ were analyzed. Effects of distortions of atomic positions in the crystal lattice on the Ω_λ and photoluminescence intensities of Eu³⁺ 4f–4f transitions were discussed. It was shown that the ideal database geometry of LaVO₄ corresponds to the highly symmetric coordination geometry of Eu³⁺ and very low Ω₂. On the contrary, experimental intensities of the ⁵D₀ → ⁷F₂ transition and the corresponding Ω₂ parameters were high. Consequently, distortions of crystal structure that reduce the symmetry play an important role in the luminescence of the LaVO₄:Eu³⁺ materials and probably other Eu³⁺-doped phosphors based on zircon-type rare earth orthovanadates

Preparation of Biocompatible, Luminescent-Plasmonic Core/Shell Nanomaterials Based on Lanthanide and Gold Nanoparticles Exhibiting SERS Effects

Multifunctional core/shell type nanomaterials composed of nanocrystalline, lanthanide doped fluorides and gold nanoparticles (Au NPs) were successfully prepared. The products were synthesized to combine luminescence properties of the core NPs, i.e., LnF₃/SiO₂–NH₂ and KLn₃F₁₀/SiO₂–NH₂, and plasmonic activity of the shell Au NPs within a single nanomaterial. The luminescent lanthanide NPs (10 or 150–200 nm) were separated from the gold NPs (6–30 nm) using an amine modified silica shell (thickness ≈30 nm). The synthesized products exhibited bright green (Tb³⁺) and red (Eu³⁺) emission under UV light irradiation. Surface modification with Au NPs influenced the product emission and luminescence decay characteristics. The luminescent-plasmonic nanomaterials were used as platforms for surface enhanced Raman scattering (SERS) measurements. 4-Mercaptobenzoic acid, choline, and T4 bacteriophages were utilized as SERS probes. For all synthesized nanomaterials, the SERS spectra for all probes studied exhibited higher intensity in comparison with the spectra measured using a commercial SERS substrate. Cytotoxicity of the products was evaluated in fibroblast cells. The results obtained showed biocompatibility of the synthesized nanomaterials in a dose-dependent manner