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In order to realize single emissive white phosphorescent organic light-emitting devices (PHOLEDs) with three color phosphorescent dopants (red, green, and blue), the energy transfer between the host material and the three dopants, as well as the among the three dopants themselves, should be considered and optimized. To explore the effect of red phosphorescent dopant on the color rendering index (CRI), the authors investigate the wavelength position of the maximum emission peak from three phosphorescent dopants. The CRI and luminous efficiency of white PHOLED in which IrðpqÞ 2 ðacacÞ acts as the red phosphorescent dopant are found to be greater than those of devices prepared using IrðpiqÞ 3 and IrðbtpÞ 2 ðacacÞ as the emission spectrum has a relatively high intensity near the human perception of blue, red, and green wavelengths. Furthermore, we demonstrate that the performance of the three dopants is related to the absorption characteristics of the red phosphorescent dopant. With a maximum emission peak at 600 nm, IrðpqÞ 2 ðacacÞ has a higher intensity in the concave section between 550 and 600 nm seen for red and blue dopants. In addition, the long metal-to-ligand charge transfer (MLCT) absorption tail of IrðpqÞ 2 ðacacÞ overlaps with the emission spectra of the green dopant, enhancing emission. Such energy transfer mechanisms are confirmed to optimize white emission in the single emissive white PHOLEDs.OCIS codes: 160.4890, 300.1030, 260.2160. doi: 10.3788/COL201715.051602.Considerable attention has been paid to white organic light-emitting devices (OLEDs) in flat panel displays (FPDs) and solid-state lighting in the next generation due to several potential advantages such as diffusive emission of surfaces, large-range area manufacturability, ecofriendliness, and effective fabrication process for the cost [1][2][3][4][5][6][7][8][9] . Such interesting advantages in white OLEDs have activated the field and, though they are entering the marketplace, outstanding challenges in achieving high efficiency and color rendering index (CRI) still remain. A key strategy for improving the efficiency in white OLEDs is to increase the external quantum efficiency to 100% by harvesting both singlet and triplet excitons. This is possible in a phosphorescent OLED (PHOLED) [10][11][12] . In the case of the longterm degradation processes, they need both optimized device structure considering organic materials in each functional layerand a good encapsulation process. Many structures have been attempted for white OLEDs to achieve a high performance [13][14][15][16][17][18] . The most easily manufacturable and simplest structures for PHOLEDs are single emissive layer (SEL) devices with phosphorescent dopants. SEL in OLEDs means only one emitting layer in the OLED device. On the other hand, multi-emissive layer (MEL) defines two, or more than two, different and distinct emitting layers in OLED devices. Though two white dopant in PHOLEDs have been realized, their low CRI makes them unsuitable for a variety of applications. It is relativ...