Microwave heating synthesis and luminescence of NaY(WO4)2:(Ho3+, Yb3+) phosphors

Abstract

NaY(WO4)2:(Ho3+, Yb3+) phosphors were synthesized by microwave heating in an EDTA-mediated process. The samples were characterized by XRD, FT-IR, SEM, and fluorescence spectrophotometer. The XRD and FT-IR results show that the samples have the tetragonal phase. The SEM results show that obtained samples have octahedral morphology. ‘Oriented attachment’ and ‘Ostwald ripening’ play key roles in the formation of octahedrons. The UC emission spectra of NaY(WO4)2:(Ho3+, Yb3+) phosphors under 980 nm excitation show two intense bands corresponding to 5F4 + 5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions. Based on the energy level diagrams of Yb3+ and Ho3+, as well as the results of power dependence of UC emission intensities, possible excitation path ways for different bands are deduced. The green and red UC emissions of NaY(WO4)2:(Ho3+, Yb3+) phosphors originate from the two-photon process. Also, the samples have good thermal stability.