Investigation of Up-conversion luminescence in Er³⁺/Yb ³⁺-codoped yttria transparent ceramic

Er³⁺/Yb³⁺-codoped Y₂O₃ transparent ceramics were fabricated and characterized from the point of up-conversion luminescence. All the samples exhibit high transparency not only in the near-infrared band but also in the visible region. Under 980 nm excitation, the ceramics gave up-conversion luminescence with very intense green (525-560 nm), red (around 660 nm), and considerably intense blue (405 nm) emissions. It is worthwhile to point out that the blue emission, which only appears in halide, was clearly observed in Y₂O₃ transparent ceramic. The emission bands at 405, 525, 560, and 660 nm are attributed to the transitions from excited states ²H_9/2, ²H_11/2, ⁴S_3/2, and ⁴F_9/2 to the ground state ⁴I_15/2 of Er³⁺ ions, respectively. For nearly all samples, the green emissions were stronger than red emissions, and the maximal emission intensities were obtained with (Er_0.025Yb_0.05Y_0.938Zr _0.01)₂O₃ ceramic (Yb/Er=20). The red and green luminescence result from a two-photon process, while the blue emission is due to a three-photon process.