3 research outputs found
Multifunctional Optical Sensors for Nanomanometry and Nanothermometry: High-Pressure and High-Temperature Upconversion Luminescence of Lanthanide-Doped PhosphatesîžLaPO<sub>4</sub>/YPO<sub>4</sub>:Yb<sup>3+</sup>âTm<sup>3+</sup>
Upconversion
luminescence of nano-sized Yb<sup>3+</sup> and Tm<sup>3+</sup> codoped
rare earth phosphates, that is, LaPO<sub>4</sub> and YPO<sub>4</sub>, has been investigated under high-pressure (HP, up to âŒ25
GPa) and high-temperature (293â773 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 (âŒ1800 cm<sup>â1</sup>),
the thermalized states of Tm<sup>3+</sup> 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 Tm<sup>3+</sup> band ratio (<sup>3</sup>F<sub>2,3</sub> â <sup>3</sup>H<sub>6</sub>/<sup>3</sup>H<sub>4</sub> â <sup>3</sup>H<sub>6</sub>), 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)
Effects of Dopant Addition on Lattice and Luminescence Intensity Parameters of Eu(III)-Doped Lanthanum Orthovanadate
A series
of La<sub>1â<i>x</i></sub>Eu<sub><i>x</i></sub>VO<sub>4</sub> samples with a different Eu<sup>3+</sup> 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 EuâO bond stretching, using a novel
approach which involved displacement of the Eu<sup>3+</sup> 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
JuddâOfelt intensity parameters Ω<sub>λ</sub>.
The effects of geometry changes caused by the dopant addition were
analyzed in terms of Ω<sub>λ</sub>. The effects of distortions
in interatomic angles of the Eu<sup>3+</sup> coordination geometry
on the Ω<sub>λ</sub> were analyzed. Effects of distortions
of atomic positions in the crystal lattice on the Ω<sub>λ</sub> and photoluminescence intensities of Eu<sup>3+</sup> 4fâ4f
transitions were discussed. It was shown that the ideal database geometry
of LaVO<sub>4</sub> corresponds to the highly symmetric coordination
geometry of Eu<sup>3+</sup> and very low Ω<sub>2</sub>. On the
contrary, experimental intensities of the <sup>5</sup>D<sub>0</sub> â <sup>7</sup>F<sub>2</sub> transition and the corresponding
Ω<sub>2</sub> parameters were high. Consequently, distortions
of crystal structure that reduce the symmetry play an important role
in the luminescence of the LaVO<sub>4</sub>:Eu<sup>3+</sup> materials
and probably other Eu<sup>3+</sup>-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., LnF<sub>3</sub>/SiO<sub>2</sub>âNH<sub>2</sub> and KLn<sub>3</sub>F<sub>10</sub>/SiO<sub>2</sub>âNH<sub>2</sub>, and plasmonic activity of the shell Au NPs within a single
nanomaterial. The luminescent lanthanide NPs (10 or 150â200
nm) were separated from the gold NPs (6â30 nm) using an amine
modified silica shell (thickness â30 nm). The synthesized products
exhibited bright green (Tb<sup>3+</sup>) and red (Eu<sup>3+</sup>)
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