Enhanced Upconversion Photoluminescence in Freestanding Er³⁺ Doped SrTiO₃ Scrolls via Strain Gradient Engineering

Abstract Lanthanide‐doped phosphors have garnered significant attention in the field of optics due to their robust upconversion luminescence capabilities. Enhancing the upconversion luminescence of these phosphors is of paramount importance. The recent advancements in fabricating ultrathin freestanding perovskite oxides present new opportunities for exploring coupled properties such as flexoelectricity. A lanthanide‐doped freestanding perovskite oxide scroll, specifically an SrTiO₃:Er scroll is introduced herein, exhibiting an average strain gradient of 9.5 × 10⁴ m⁻¹. The developed scroll structure achieves a remarkable enhancement in upconversion luminescence, with a maximum increase of 7.4 times at the wavelength of 548 nm, driven by the synergistic effects of ferroelectricity and flexoelectricity. Theoretical model is adopted to elucidate the relationship between the scroll structure and strain, further investigating the mechanisms underlying the photoluminescence enhancement. This work unveils a novel three–dimensional (3D) tubular platform for enhancing the luminescence of phosphors without structural constraints, facilitating integration with silicon photonics.