Vibrational and luminescent properties of LaPO4:Eu3+ with different preparation conditions

Spectroscopic study of the 4fn-15dtransitions of LaPO4doped with Pr3+ or co-doped with Pr3+ and Gd3+ in the vacuum ultra violet region

The energy off-dtransitions depends on the crystalline field in which the lanthanide ion is inserted. Depending on the experimental setup, these transitions could occur at high energy, so several studies regarding theoretical data have been conducted. Here, we present the experimental determination of the energy of interconfigurational 4fⁿ → 4f^n-15d (f-d)transitions from Pr³⁺ions to the lanthanum orthophosphate LaPO₄matrix; we have also determined the bandgap value for this host. The experiments were carried out at the Synchrotron setup of the Brazilian LNLS laboratory. Specifically, we synthesized LaPO₄:Pr³⁺and LaPO₄:Pr³⁺/Gd³⁺by the hydrothermal method under different pH conditions or by spray pyrolysis. The particles resulting from hydrothermal synthesis had different morphologies and the influence of pH value was showed: the reaction medium was controlled along the process, which changed the surface potential. On the basis of Raman spectroscopy and x-ray diffraction analyses, we found that the crystalline phase was monoclinic monazite for all the samples. We studied the 4f5dlevel and bandgap transitions at high energy by absorption analysis in the VUV range. The experimental results were 7.5 eV (LaPO₄bandgap) and 5 eV (4fⁿ→ 4f^n-15dtransition of the Pr³⁺ion), which were close to the theoretical values reported in the literature for this ion and this matrix.

1D Ceric Hydrogen Phosphate Aerogels: Noncarbonaceous Ultraflyweight Monolithic Aerogels

Ceric hydrogen phosphate gels possess a very unique spatial organization, being nearly amorphous materials with a fibrous structure. Using a sol-gel approach, we succeeded in preparing bulky gels containing as much as 20,000 molecules of water per cerium atom. Supercritical treatment of these gels made it possible to obtain the first ultralight monolithic noncarbonaceous aerogels with a density as low as 1 mg/cm3.

Luminescence properties of a novel red phosphor 6LaPO4 -3La3 PO7 -2La7 P3 O18 :Eu3

Eu³⁺ -doped 6LaPO₄ -3La₃ PO₇ -2La₇ P₃ O₁₈ red luminescent phosphors were synthesized by co-deposition and high-temperature solid-state methods and its polyphase state was confirmed by X-ray diffraction analysis. Transmission electron microscopy showed the grain morphology as a mixture of rods and spheres. Luminescence properties of the phosphor were investigated and its red emission parameters were evaluated as a function of Eu³⁺ concentration (3.00-6.00 mol%). Excitation spectra of 6LaPO₄ -3La₃ PO₇ -2La₇ P₃ O₁₈ :Eu³⁺ showed strong absorption bands at 280, 395, and 466 nm, while the luminescence spectra exhibited prominent red emission peak centred at 615 nm (⁵ D₀ →⁷ F₂ ) in the red region. CIE chromaticity coordinates of the 6LaPO₄ -3La₃ PO₇ -2La₇ P₃ O₁₈ :5%Eu³⁺ phosphor were (0.668, 0.313) in the red region, and defined its potential application as a red phosphor.

Facile synthesis of colloidal photoluminescent BiPO4:Ln (Eu,Tb) nanoparticles well-dispersed in polar solvents

Colloidal photoluminescence BiPO₄:Ln (Eu,Tb) nanoparticles well-dispersed in polar solvents have been prepared, which exhibit organic-red and green colours under UV irradiation.

LaPO4:Eu fluorescent nanorods, synthesis, characterization and spectroscopic studies on interaction with human serum albumin

Eu³⁺ doped LaPO₄ fluorescent nanorods (LaPO₄:Eu) was successfully fabricated by a hydrothermal process. The obtained LaPO₄:Eu nanorods under the optimal conditions were characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR), UV-vis absorption and fluorescence spectroscopy. The nanorods with a length of 50-100nm and a diameter of about 10nm, can emit strong red fluorescence upon excitation at 241nm. The FTIR result confirmed that there are lots of phosphate groups on the surfaces of nanorods. In order to better understand the physiological behavior of nanorods in human body, multiple spectroscopic methods were used to study the interaction between the LaPO₄:Eu nanorods and human serum albumin (HSA) in the simulated physiological conditions. The results indicated that the nanorods can effectively quench the intrinsic fluorescence of HSA through a dynamic quenching mode with the association constants of the order of 10³Lmol^-1. The values of the thermodynamic parameters suggested that the binding of the nanorods to HSA was a spontaneous process and van der Waals forces and hydrogen bonds played a predominant role. The displacement experiments verified that the binding site of nanorods on HSA was mainly located in the hydrophobic pocket of subdomain IIA (site I) of HSA. The binding distance between nanorods and HSA was calculated to be 4.2nm according to the theory of Förster non-radiation energy transfer. The analysis of synchronous fluorescence, three-dimensional fluorescence (3D) and circular dichroism (CD) spectra indicated that there the addition of LaPO₄:Eu nanorods did not caused significant alterations in conformation of HSA secondary structure and the polarity around the amino acid residues.