White organic light-emitting devices (WOLEDs) consist of a fluorescent blue material doped in a region spatially separate from the phosphorescent dopant iridium complex. This study evaluated two potential new phosphorescent materials, the heteroleptic tris-cyclometallated iridium complexes Ir(tpy)(2)(btp) and Ir(btp)(2)(tpy), where tpy and btp are "2-(p-tolyl)pyridine'' and "2-(2'-benzothienyl) pyridine'', respectively. The luminescence mechanism in heteroleptic iridium complexes is determined by the rates of decay from two different species of ligands. The quantum yields (lifetime) of fac-Ir(tpy)(3) and fac-Ir(btp)(3) were reported as 0.5 (2.0 mu s) and 0.12 (4.0 mu s), respectively. Thus, the radiative decay rate (k(r)) of fac-Ir(tpy)(3) and fac-Ir(btp)(3) can be calculated as 2.5 x 10(5)/s and 3.0 x 10(4)/s, respectively. Heteroleptic tris-cyclometallated iridium complexes were able to tune the color for white phosphorescent materials, by controlling the radiative decay rate of ligands and number of ligands in complexes.