Thermoluminescence (TL) properties of Ce(3+) and Yb(3+) co-doped in Y(3)Al(5)O(12) (YAG) were studied with the aim of determining the location of energy levels of Ce(3+) and Yb(2+) relative to the bottom of the conduction band (CB) and the top of the valence band (VB) of YAG. The TL glow peak at about 180 °C when heating rate β = 1°C s(-1) was assigned to electron release from Yb(2+), indicating that Yb(3+) acts as an electron trap. The trap depth, which is the depth of the ground-state level of Yb(2+) below the bottom of the CB, was derived from the temperatures of the maximum of the TL glow peak at different heating rates. The value is, within the experimental and theoretical uncertainties, in good agreement with that derived from the O(2-) --> Yb(3+) charge transfer energy. Thermoluminescence excitation spectroscopy (TLES) was used to establish the location of energy levels of Ce(3+). From the derived data the energy level diagram of YAG:Ce(3+), Yb(3+) is constructed and possible electron transfer processes are discussed.