Effects of Na+-doping on the structure and luminescence properties of Li1-xNaxBi(MoO4)2: Yb3+/Ho3+ phosphors

Abstract

In this study, a series of Li1-xNaxBi (MoO4)2: 0.3 Yb3+, 0.01Ho3+ (x = 0–1) phosphors were prepared using a high-temperature solid-state reaction method. The as-prepared sample produced high-intensity green light (542 nm) and weak red light (646 nm) under the excitation of a 980 nm laser, which was generated by the radiative relaxation of 5S2/5F4→5I8 and 5F5→5I8 energy levels in Ho3+. We performed X-ray diffraction (XRD) tests on our samples, the XRD test data show that the incorporation of Yb3+ and Ho3+ shrank the lattice, and the luminescence intensity improved after doping with Na+. With an increase in Na+ concentration, two inflection points were observed in the luminescence intensity. The luminescence intensity was strongest when the Na+ concentration was 30% and 80%; moreover, it was also the inflection point of the 2θ value of the strongest diffraction peak (112) of the sample. By fitting the pump power and the up-converted luminescence intensity, it was inferred that the emission of one photon at 542 and 646 nm requires the absorption of three photons. Using the fluorescence decay time test, it was observed that the 2θ value corresponding to the strongest diffraction peak of the sample had a corresponding relationship with the fluorescence lifetime. Therefore, this study provides a reference for the further exploration of ion substituted upconversion luminescent materials.