Synthesis and distinct up-converting behaviors of Er3+, Yb3+ doped LaOF and LaO0.65F1.7 phosphors

Abstract Optical materials composed of tetragonal La1-x-yErxYbyO0.65F1.7 (x = 0.005–0.1, y = 0–0.1) and from tetragonal and trigonal La0.99Er0.005Yb0.01OF were prepared via a solid-state reaction using an excess of NH4F flux at 950 or 1050 °C for 2 h. X-ray diffraction patterns of La1-x-yErxYbyO0.65F1.7 and La0.99Er0.005Yb0.01OF were obtained using different molar ratios of the NH4F: La(Er,Yb)O3/2. The effective spectral conversion properties of Er3+-Yb3+ ions in non-stoichiometric LaO0.65F1.7 host lattices were monitored upon excitation of the samples using a 980 nm diode-laser. By selecting appropriate Er3+ and/or Yb3+ concentrations in the LaO0.65F1.7 matrix, up-conversion emission at desired wavelengths in the green to red region of the spectrum was obtained. Furthermore, the mechanism of up-conversion in the nonstoichiometric LaO0.65F1.7 phosphors was described with the help of an energy-level schematic. Up-converted emission spectra and the dependence of the emission intensity on pump power in the La1-x-yErxYbyO0.65F1.7 phosphors were also investigated.