Nanopartículas de óxidos binários a base de SiO2 e Gd2O3 dopados com terras raras para conversão de energia via upconversion e downshiffting

Abstract

Rare Earth (RE) based materials stand out for their unique optical properties, such as the conversion of energy between different wavelengths, with applications in various areas. This study presents the synthesis, structural, and spectroscopic characterization of SiO2-Gd2O3 materials doped with Er3+, Yb3+, and Eu3+ (Er3+: 0.0–0.3; Yb3+: 0.0–1.2; Eu3+: 0.0–7.0 mol%) for use as energy converters. The materials were synthesized using the sol-gel method and thermally treated for 8 hours at 900 °C. X-ray diffraction (XRD) analysis revealed sharp and intense peaks associated with the formation of crystalline Gd2O3 in a cubic structure with space group Ia3 (206), with efficient incorporation of dopants into the matrix. Rietveld refinement showed increases in lattice parameter values, microstrain from 0.221 to 0.524%, and crystallite sizes between 55.38 and 163.37 nm. FTIR and Raman spectroscopy confirmed the presence of bands corresponding to both cubic Gd2O3and SiO2. UV-Vis spectroscopy revealed absorption bands associated with the matrix and the three dopants, with calculated from 4.98 to 5.18 eV. Scanning electron microscopy (SEM) revealed polyhedral rods and nanostructures with irregular shapes and sizes, with no apparent influence of the dopants on the matrix morphology. Transmission electron microscopy (TEM) analysis indicated heterogeneous Gd2O3 crystalline nanoparticles dispersed in amorphous silica. Energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of all elements in the material, as well as the EDS maps presented the formation and distribution of NPs within the silica matrix. Photoluminescence spectroscopy demonstrated successful downshifting under excitation at 266 nm and 390 nm, with visible emissions in the 460–720 nm range, attributed to Eu³⁺ and Er3+. Excited-state lifetimes under 405 nm excitation ranged from 0.567 ms to 1.556 ms at 611.5 nm emission and from 0.291 ms to 1.617 ms for Er3+ transitions at 650.5 nm. Furthermore, the upconversion was observed under 800 nm excitation, with emissions between 525 and 575 nm characteristic of Er³⁺ ions. The SGEY, SGEYE1 and SGEYE5 materials were tested for their cytotoxicity and the results indicated that they have a low toxicity profile against SKOV-3 cells, especially at lower Eu3+ concentrations. Exhibiting both upconversion and downshifting processes, the SiO2-Gd2O3:Er3+/Yb3+/Eu3+ materials (Er3+: 0.0–0.3; Yb3+: 0.0–1.2; Eu3+: 0.0–7.0 mol%) thermally treated at 900 °C for 8 hours are promising candidates for energy conversion applications in photonics.