Two different trapping and detrapping processes of chargecarriers have been investigated in GdAlO3:Ce3+,Ln3+(Ln = Pr, Er, Nd, Ho, Dy,Tm, Eu, and Yb) and GdAlO3:Ln3+,RE3+(Ln = Sm, Eu, and Yb; RE = Ce, Pr,and Tb). Cerium is the recombination center and lanthanide codopants act aselectron-trapping centers in GdAlO3:Ce3+,Ln3+.Different lanthanide codopantsgenerate different trap depths. The captured electrons released from thelanthanide recombine at cerium via the conduction band, eventually producingthe broad 5d−4f emission centered at∼360 nm from Ce3+. On the other hand,Sm3+,Eu3+, and Yb3+act as recombination centers, while Ce3+,Pr3+, and Tb3+actas hole-trapping centers in GdAlO3:Ln3+,RE3+. In this situation, wefindevidence that recombination is by means of hole release instead of the morecommonly reported electron release. The trapped holes are released from Pr4+or Tb4+and recombine with the trapped electrons on Sm2+,Eu2+,orYb2+andyield characteristic trivalent emission from Sm3+,Eu3+,orYb3+at∼600,∼617, or∼980 nm, respectively. Lanthanum wasintroduced to engineer the valence band energy and change the trap depth in Gd1−xLaxAlO3:Eu3+,Pr3+andGd1−xLaxAlO3:Eu3+,Tb3+. The results show that the valence band moves upward and the trap depth related to Pr3+or Tb3+decreases.