Efficient green up-conversion emission in Yb³⁺/Ho³⁺ co-doped CaIn₂O₄

Intense green up-conversion (UC) emissions from ⁵F ₄/⁵S₂ → ⁵I₈ transitions of Ho³⁺ in Yb³⁺/Ho³⁺ co-doped CaIn₂O₄ have been observed with excitation at 980 nm. The optimal processing parameters were determined by investigating emission intensities as a function of annealing temperature, duration time and Ho ³⁺/Yb³⁺ dopant concentrations. It has been confirmed that the green UC luminescence was generated via a two-photon process from the quadratic dependence of the emission intensity on the pump power. A UC mechanism was proposed and the lifetime of the green emission was measured to be ∼204 μs. The infrared-to-visible UC efficiency of the optimized CaIn ₂O₄: 0.005Ho³⁺, 0.1Yb³⁺ sample increases to ∼5.5% with the excitation power and saturates at 1.5 W. The chromaticity coordinates (0.281, 0.708) of the samples are located in the green region and hardly changed due to the negligible red emission. The results indicate that CaIn₂O₄: Yb³⁺, Ho³⁺ could act as an effective UC green light emitter and CaIn₂O ₄ is an ideal oxide host for UC luminescence.