Impact of Structural Changes on Energy Transfer in the Anion-Engineered Re³⁺:Y₂O₃ Through Low-Temperature Synthesis...

Anion engineering has proven to be an effective strategy to tailor the physical and chemical properties of metal oxides by modifying their existing crystal structures. In this work, a low-temperature synthesis for rare earth (RE)-doped Y₂O₂SO₄ and Y₂O₂S was developed via annealing of Y(OH)₃ intermediates in the presence of elemental sulfur in a sealed tube, followed by a controlled reduction step. The crystal structure patterns (X-ray diffraction) and optical spectra (UV-IR) of Y₂O₂SO₄, Y₂O₂S, and crystalline Y₂O₃ were collected throughout the treatment steps to correlate the structural transformations (via thermogravimetric analysis) with the optical properties. Local and long-range crystallinities were characterized by using X-ray and optical spectroscopy approaches. Systematic shifts in the Eu³⁺ excitation and emission peaks were observed as a function of SO₄^2- and S^2- concentrations resulting from a crystal evolution from cubic (Y₂O₃) to trigonal (Y₂O₂S) and monoclinic (Y₂O₂SO₄), which can modify the local hybridization of sensitizer dopants (i.e., Ce³⁺). Ultimately, Tb³⁺ and Tb³⁺/Ce³⁺ doping was employed in these hosts (Y₂O₂SO_4, Y₂O₂S, and Y₂O₃) to understand energy transfer between sensitizer and activator ions, which showed significant enhancement for the monoclinic sulfate structure.