Controlled Electron–Hole Trapping and Detrapping Process in GdAlO₃ by Valence Band Engineering

Two different trapping and detrapping processes of charge carriers have been investigated in GdAlO 3:Ce 3+,Ln 3+ (Ln = Pr, Er, Nd, Ho, Dy, Tm, Eu, and Yb) and GdAlO 3:Ln 3+,RE 3+ (Ln = Sm, Eu, and Yb; RE = Ce, Pr, and Tb). Cerium is the recombination center and lanthanide codopants act as electron-trapping centers in GdAlO 3:Ce 3+,Ln 3+ . Different lanthanide codopants generate different trap depths. The captured electrons released from the lanthanide recombine at cerium via the conduction band, eventually producing the broad 5d–4f emission centered at ∼360 nm from Ce 3+ . On the other hand, Sm 3+, Eu 3+, and Yb 3+ act as recombination centers, while Ce 3+, Pr 3+, and Tb 3+ act as hole-trapping centers in GdAlO 3: Ln 3+,RE 3+ . In this situation, we find evidence that recombination is by means of hole release instead of the more commonly reported electron release. The trapped holes are released from Pr 4+ or Tb 4+ and recombine with the trapped electrons on Sm 2+, Eu 2+, or Yb 2+ and yield characteristic trivalent emission from Sm 3+, Eu 3+, or Yb 3+ at ∼600, ∼617, or ∼980 nm, respectively. Lanthanum was introduced to engineer the valence band energy and change the trap depth in Gd 1– x La x AlO 3:Eu 3+,Pr 3+ and Gd 1– x La x AlO 3:Eu 3+,Tb 3+ . The results show that the valence band moves upward and the trap depth related to Pr 3+ or Tb 3+ decreases.