Hole Detrapping-Type Persistent Phosphors of RE2O2S (RE = La, Gd, Y, Lu) Doped with Eu3+-Pr3+ and Eu3+-Tb3+
Atsunori Hashimoto (Japan Advanced Institute of Science and Technology, NEMOTO & CO.)
Jumpei Ueda (Japan Advanced Institute of Science and Technology, Kyoto University)
Yasushi Aoki (NEMOTO & CO.)
P. Dorenbos (TU Delft - RST/Luminescence Materials)
Setsuhisa Tanabe (Kyoto University)
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Abstract
RE2O2S:Eu3+-Ln3+ (RE = La, Gd, Y, Lu; Ln = Pr, Tb) samples were prepared by a solid-state reaction method to develop new red persistent phosphors and to demonstrate the hole detrapping mechanism. All Eu3+-singly doped RE2O2S show very weak thermoluminescence (TL) glow peaks, while by codoping Pr3+ or Tb3+ ions, additional strong TL peaks were observed. In the TL spectra and persistent luminescence (PersL) spectra, only Eu3+ luminescence lines were observed, but there was no Pr3+ and Tb3+ luminescence. From the PersL excitation spectra, it is found that PersL is caused after excitation to the charge transfer state of Eu2+-S- in which the hole is in the valence band. These results show that Eu3+ acts as a recombination center and Pr3+ and Tb3+ ions act as hole trap centers. The deeper hole trap depth of Pr3+ than that of Tb3+ and the RE dependence of hole trap depth are explained using a vacuum referred binding energy diagram considering the nephelauxetic effect. La2O2S:Eu3+-Pr3+ was the best composition among the samples as a persistent phosphor at ambient temperature, showing strong red persistent luminescence in a short time range (>100 mcd/m2 for a few seconds).