Enhanced bright green luminescence from GdOF:Ho³⁺ up-conversion phosphor via Yb³⁺ doping

In this paper, a series of GdOF-based green phosphors doped with Ho³⁺ and Yb³⁺ ions was prepared by a simple co-precipitation method. The crystal structures and optical properties were investigated in detail. The intensity of the emission of GdOF:Yb³⁺,Ho³⁺ phosphors is enhanced by the effective energy transfer from Yb³⁺ to Ho³⁺, and the optimal luminescence is achieved with the Ho³⁺ doping amount of 0.1 mol% as well as Yb³⁺ doping amount of 5 mol%. Tunable UC emission of samples is achieved by adjusting the doping concentration of Ho³⁺ or Yb³⁺. The purity of the green UC emission is further improved by enhancing the excitation pumping power. In addition, logarithmic functions of green, red and near-infrared radiation intensities were calculated versus logarithmic function of pump power for further study. A possible UC luminescence mechanism between Yb³⁺ and Ho³⁺ is discussed based on power-dependent UC luminescence spectrum and decay lifetimes. These results suggest that GdOF:Yb³⁺,Ho³⁺ phosphors with bright and high-purity green UC emission have potential applications in the fields of bioimaging, display and illumination.