Frequency upconversion fluorescence studies of Er3+/Yb3+-codoped KNbO3 phosphors

Different concentrations of Er3+ and Yb3+ ions-doped potassium niobate (K0.9NbO3:Yb(x)Er(0.1 − x) for x = 0, 0.01, 0.05, 0.09 and 0.1) polycrystalline powder phosphors were prepared by the conventional solid state reaction method and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Energy transfer and upconversion fluorescence properties of the Yb3+ and Er3+-codoped phosphors have been discussed. The XRD data has shown mono-phase for pure KNbO3 while the doped samples represented additional phase formation. The SEM micrographs represented the rectangular crystal growth habit for the KNbO3 phosphors when doped with 0.1 mol of Er3+ ions. An intense green emission at 557 nm along with a red emission at 674 nm was observed when the doped samples were excited with 975 nm IR radiation. The upconversion mechanism has been discussed based on the excited state absorption and energy transfer mechanisms.