In this paper, we performed the design on the relative thickness of fluorescent-phosphorescent light emitters and evaluated the corresponding change of spectral characteristics of white organic light emitting diode (WOLED). Use of a 3-nm-thick separator composed of undoped phosphorescent host, which provides the confinement of singlet exciton, yields relatively well-defined broadband white emission. The optimized multilayers in WOLED comprises one of the simplest device structures among the reported fluorescent-phosphorescent hybrid WOLEDs. representing the Commission Internationale de I'Eclairage (CIE) 1931 chromaticity ranging from the nearly pure (0.30, 0.35) to warm white (0.35, 0.40) of 9.0-12.5 cd/A (24,000 cd/m(2) at 12 V bias). Although the presented efficiency data is not as high as the reports of others, design principles for a bright and stabilized three-peak-balanced white emission are discussed in detail, which will be beneficial for a step forwards in the development of broadband WOLED. (C) 2008 Elsevier B.V. All rights reserved.