Simultaneous excitation at IR and UV of RE3+ triply doped SiO2-Gd2O3 materials for energy conversion purposes

Most traditional photoactive materials for solar cell applications are sensitive to visible light, which highlights the importance of materials that are also active in the ultraviolet (UV) and infrared (IR) regions for an increase in energy conversion efficiency. SiO2-Gd2O3:Er3+/Yb3+/Eu3+ (xEr: 0.0-0.3; xYb: 0.0-1.2; xEu: 0.0-7.0 mol%) materials were prepared via sol-gel method, followed by thermal treatment at 900 degrees C for 8 h. The Gd2O3 crystalline cubic structure was determined by XRD and FT-IR, and the lattice parameters were investigated by Rietveld Refinement. Besides, the morphology was observed by SEM micrographs as a system in which Gd2O3 particles are dispersed in SiO2. In the EDX spectra. It was registered narrow bands arising from Er3+, Yb3+, and Eu3+ doping elements, besides Si4+, Gd3+, and O2-, confirming the presence of these elements in the composition. Under IR excitation at 980 nm, the samples showed upconversion phenomena, with Yb3+ ions working as sensitizers, and effective energy transfer between the doping RE3+ ions. The emission bands in the visible region are attributed to transitions of Er3+ ion, and Eu3+ ion transitions (enhanced up 66 times). Under UV excitation at 247.5 nm, it was observed the down shifting process, seen as narrow bands related to Eu3+ ion transitions. The samples showed red emission colors as the Eu3+ concentrations increased in the matrix for upconversion and down shifting process. The results suggest that xEu: 1.0 mol% is the optimal doping level of Eu3+ in the SiO2-Gd2O3 system. This triply doped sample was simultaneously excited at 980 nm and 247.5 nm. It was observed Eu3+ and Er3+ narrow bands in the visible region, responsible for both upconversion and down shifting process when doubly excited. For all these reasons, the materials are promising to be applied to the field of energy conversion and solar cell applications.