Intense and color-tunable upconversion luminescence of Er3+ doped and Er3+/Yb3+ co-doped Ba3Lu4O9 phosphors

Abstract

A series of novel Er3+ doped and Er3+/Yb3+ co-doped Ba3Lu4O9 phosphors were synthesized by a simple high-temperature solid-state reaction method. The crystal structure and morphology of the samples were identified by XRD and SEM analysis. Under 980 nm laser diode excitation, the green (at 537 nm and 560 nm) and red (at 660 nm) UC emission were observed, which could be attributed to the (2H11/2, 4S3/2)→4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. The UC luminescence can be finely tuned from green to dark-yellow light to some extent by increasing Yb3+ doping concentration. The sintering temperature and doping concentration of Ba3Lu4-x-yO9: x Er3+, y Yb3+ were optimized to x = 0.1 and y = 0.6 at 1550 °C. The emission intensity ratio of Green/Red keeps declining monotonically with increasing Er3+ or Yb3+ concentration, which is due to the cross-relaxation effect and cooperative energy transfer between the two neighboring Er3+ ions-as well as back energy transfer from Er3+ to Yb3+ ions. Based on the pump-power dependence and UC luminescence decay curves, the energy level diagram and the possible energy transfer mechanism of Er3+ doped as well as Er3+/Yb3+ co-doped system were investigated in detail. In addition, according to the energy gap law, the possibilities of non-radiative transition between parts of energy levels of Er3+ ions were calculated.