Up-Conversion Luminescence of Er3+/Pr3+/Yb3+ Co-doped LaNbO4 Phosphors
Er3+–Pr3+–Yb3+ co-doped LaNbO4 (LNO) phosphors were obtained by solid-state reaction and their up-conversion properties have been studied. The x-ray diffraction and Rietveld’s refinement revealed no evidence of significant structural changes or secondary phases in the synthesized materials. According to the up-conversion measurements, the observed emissions are due to Er3+ ions which are present as unintentional contaminant in the Pr3+ doped and Pr3+–Yb3+ co-doped systems. The intensity of all the bands was enhanced with increasing Yb3+ concentration, and at 8%Yb3+ a significant decrease of the green and red emissions was found due to the presence of cross-relaxation process between Er3+ and Pr3+ ions, mainly for green emissions because of the back energy transfer mechanisms from Er3+ to Yb3+. The Commission Internationale de l’éclairage color coordinates of almost all samples were located in the green region, while for the LNO: Pr 0.1%–Yb8% phosphor they were located in the blue region. Red–Green–Blue phosphors were obtained from LaNbO4: Pr3+/Er3+/Yb3+ systems using the pair of activators Pr3+/Er3+ which is not commonly investigated in the literature.