Visualizing hidden electron trap levels in Gd_3Al_2Ga_3O_(12):Ce crystals using a mid-infrared free-electron laser

摘要

The energy levels of electron traps (namely, defect complexes associated with oxygen vacancies) in Gd_3Al_2Ga_3O_(12):Ce (GAGG:Ce) were studied at 12 K using mid-infrared (MIR) light pulses from a free-electron laser (FEL) as the probe light. Ce~(3+) 5d-4f luminescence was stimulated by the MIR light pulse following an ultraviolet light pulse. Stimulation of Ce~(3+) 5d-4f luminescence by MIR light pulses was pronounced above 0.31 eV. This result is consistent with that of previous work based on a trap-mediated luminescence model. It is concluded that the electron trap levels are located 0.31 eV below the bottom of the conduction band. This study demonstrates that MIR-FEL is applicable for the determination of hidden electron trap levels.