Formation of Deep Electron Traps by Yb Codoping Leads to Super-Long Persistent Luminescence in Ce-Doped Yttrium Aluminum Gallium Garnet Phosphors.

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