Subwavelength silica particle layers have been applied between glass and thin film luminescent layers of Alq3 and a polymer MEH-PPV layer, respectively. The layers acted as a randomised two-dimensional diffraction lattice, which increased the fraction of emitted power from thin film organic layers into air. In contrast to perfectly ordered structures strong interference emission patterns did not occur. Still, an optical feedback of the particle layer on the emission spectrum could be observed, which can be used to improve colour saturation for blue and green emission and to increase the lumen efficiency for red emission, without changing the colour point of the red emitter.
In photoluminescence experiments a gain factor of 3 and 2.5 in light outcoupling was realized for Alq3 and MEH-PPV layers, respectively. With a MEH-PPV polymer OLED device an efficiency gain of 30 to 40 % has been realized in electroluminescence.