Hybrid excitation mechanism of upconversion fluorescence in hollow La₂Ti₂O₇ : Tm³⁺/Yb³⁺ submicron fibers

High-crystalline, hollow-mesh-like Tm³⁺/Yb³⁺-co-doped La₂Ti₂O₇ (LTO) submicron fibers are prepared by electrospinning technique and identified as monoclinic structure. The LTO matrix fibers and the Tm³⁺/Yb³⁺-co-doped fibers exhibit different frequency upconversion luminescence. The fluorescence of the matrix at the 487 and 542 nm is ascribed to the two-photon absorption and the cross-relaxation processes caused by the defect center at 977 nm excitation, respectively. The upconversion luminescence intensity enhances when the rare-earth ions are incorporated into LTO fibers. The emissions of Tm³⁺ in co-doped LTO membranes at 479 and 789 nm under the excitation of 977 nm indicate the effectiveness of the three- and two-photon absorption processes, respectively. The pristine LTO fibers have the potential to be employed for water purification as a laser-excited photocatalytic material because the LTO materials are conducive to absorbing the highly penetrating NIR laser. Furthermore, the Tm³⁺/Yb³⁺ ions play a positive role in further promoting the laser-absorption capacity, and the hybrid excitation mechanism in the Tm³⁺/Yb³⁺-co-doped LTO composite fibers provides a new perspective for the development of anti-laser inorganic materials.