Tunable dual-mode photoluminescences from SrAl2O4: Eu/Yb nanofibers by different atmospheric annealing.

• The SrAl2O4:Eu/Yb nanofibers were fabricated via a facile electrospinning method. • The optical emission modulation is attributed to the valence of Eu. • Tuning the valence of Eu lies on adjusting the annealing routes. • The tailoring of single UC, DC and dual-mode UC/DC optical emission could be realized. ga1 One-dimensional Eu/Yb co-doped SrAl 2 O 4 nanofibers were successfully synthesized via an electrospinning technique. The morphologies, crystal structures, and chemical valences were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. The results revealed that the valence of Eu ions was primary trivalent (Eu3+) after annealing in oxygen ambient (air), and the red up-conversion (UC) luminescence was observed which was derived from 5D 0–2 to ground state 7F J (J = 0–6) of Eu3+ ions. While they evolved to bivalent (Eu2+) after annealing in a reduced (H 2 /Ar) ambient, showing green down-conversion (DC) luminescence under the exposure of 365 nm, which was ascribed to Eu2+ 4 f -5 d allowed transition. The mixed valence of Eu2+/Eu3+ could be realized through a partially oxidation in air again, strikingly, resulting in dual-mode UC and DC. Herein, we demonstrate the tunable dual-mode UC and DC emission performance in SrAl 2 O 4 : Eu/Yb nanofibers through selective annealing processes. Consequently, the synthesized SrAl 2 O 4 : Eu/Yb nanofibers may offer potentials applications towards multifunctional luminescent occasion. [ABSTRACT FROM AUTHOR]