White light emitting devices were fabricated using blue emitting organic light emitting diodes (OLEDs) and down-conversion phosphor mixtures. Three different thicknesses of yellow and mixtures of yellow and red luminescent phosphor films were prepared on separate glass slides using a silicone matrix. The down-conversion films were optimized by varying the thickness and phosphor to silicone weight ratio. The phosphor films with different thickness were coupled to an optimized blue emitting OLED with a refractive index matching gel. Optimized down-conversion phosphor layers integrated with blue OLEDs exhibited 2× enhancement of efficiency (lumens per electrical Watt) for white to that of the blue OLED. The International Commission of Illumination color coordinates and average color rendering index for this device were (0.43, 0.46) and >80, respectively.