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 GdAlO3:Ce3+,Ln(3+) (Ln = Pr, Er, Nd, Ho, Dy, Tm, Eu, and Yb) and GdAlO3:Ln(3+),RE3+ (Ln = Sm, Eu, and Yb; RE = Ce, Pr, and Tb). Cerium is the recombination center and lanthanide codopants act as electron-trapping centers in GdAlO3:Ce3+,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 similar to 360 nm from Ce3+. On the other hand, Sm3+, Eu3+, and Yb3+ act as recombination centers, while Ce3+, Pr3+, and Tb3+ act as hole-trapping centers in GdAlO3: Ln(3+),RE3+. 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 Pr4+ or Tb4+ and recombine with the trapped electrons on Sm2+, Eu2+, or Yb2+ and yield characteristic trivalent emission from Sm3+, Eu3+, or Yb3+ at similar to 600, similar to 617, or similar to 980 nm, respectively. Lanthanum was introduced to engineer the valence band energy and change the trap depth in Gd1-xLaxAlO3:Eu3+,Pr3+ and Gd1-xLaxAlO3:Eu3+,Tb3+. The results show that the valence band moves upward and the trap depth related to Pr3+ or Tb3+ decreases.