Formation of Deep Electron Traps by Yb3+ Codoping Leads to Super-Long Persistent Luminescence in Ce3+-Doped Yttrium Aluminum Gallium Garnet Phosphors

Abstract

The Y₃Al₂Ga₃O₁₂:Ce³⁺-Cr³⁺ compound is one of the brightest persistent phosphors, but its persistent luminescence duration is not so long because of the relatively shallow Cr³⁺ electron trap. To compare the vacuum referred binding energy of the electron trapping state by Cr³⁺ and lanthanide ions, we selected Yb³⁺ as a deeper electron trapping center. The Y₃Al₂Ga₃O₁₂:Ce³⁺-Yb³⁺ phosphors show Ce³⁺:5d → 4f green persistent luminescence after blue light excitation. The formation of Yb²⁺ was confirmed by the increased intensity of absorption due to Yb²⁺:4f-5d at 585 nm during the charging process. This result indicates that the Yb³⁺ ions act as electron traps by capturing an electron. From the thermoluminescence glow curves, it was found that the Yb³⁺ trap makes a much deeper electron trap with a 1.01 eV depth than the Cr³⁺ electron trap with a 0.81 eV depth. This deeper Yb³⁺ trap provides a much slower detrapping rate of filled electron traps than the Cr³⁺-codoped persistent phosphor. In addition, by preparing transparent ceramics and optimizing Ce³⁺ and Yb³⁺ concentrations, the Y₃Al₂Ga₃O₁₂:Ce³⁺(0.2%)-Yb³⁺(0.1%) as-made transparent ceramic phosphor showed super-long persistent luminescence for over 138.8 h after blue light charging.

Keywords: Ce3+; garnet; persistent luminescence; trap engineering; valence-state change.