Although lanthanide complexes have distinct advantages for use as light-emitting materials, such as sharp emission bands and 100% quantum efficiency theoretically, their performance was far below what is expected. A new terbium complex was designed and synthesized. Devices using it as an emitter present satisfactory performance, with the highest brightness of 12 000 cd/m2 and power efficiency of 11.3 lm/W, which is nearly 1 order of magnitude higher than what was reported previously. Comparison with analogous complexes indicated that this result originated from the terbium complex's well-balanced charge-transport properties.