A novel yellowish-green triplet emitter, bis(5-(trifluoromethyl)-2-p-tolylpyridine) (acetylacetonate)iridium(III) (1), was conveniently synthesized and used in the fabrication of both monochromatic and white organic light-emitting diodes (WOLEDs). At the optimal doping concentration, monochromatic devices based on 1 exhibit a high efficiency of 63 cd A−1 (16.3% and 36.6 lm W−1) at a luminance of 100 cd m−2. By combining 1 with a phosphorescent sky-blue emitter, bis(3,5-difluoro-2-(2-pyridyl)phenyl)-(2-carboxypyridyl)iridium(III) (FIrPic), and a red emitter, bis(2-benzo[b]thiophen-2-yl-pyridine)(acetylacetonate)iridium(III) (Ir(btp)2(acac)), the resulting electrophosphorescent WOLEDs show three evenly separated main peaks and give a high efficiency of 34.2 cd A−1 (13.2% and 18.5 lm W−1) at a luminance of 100 cd m−2. When 1 is mixed with a deep-blue fluorescent emitter, 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi), and Ir(btp)2(acac), the resulting hybrid WOLEDs demonstrate a high color-rendering index of 91.2 and CIE coordinates of (0.32, 0.34). The efficient and highly color-pure WOLEDs based on 1 with evenly separated red, green, blue peaks and a high color-rendering index outperform those of the state-of-the-art emitter, fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)3), and are ideal candidates for display and lighting applications.