The optical properties of OLEDs can be tailored by optimization of the layer stack and by implementation of micro- and/or nano-optical structures. But the effect of changing the OLED configuration on the device performance crucially depends on the optical properties of the emissive layer. The aim of this contribution is twofold. First, we will propose and demonstrate a general and reliable method to determine the intrinsic optical emitter properties via simple optical characterization and corresponding reverse simulations. Second, the influence of the emitter properties on homogeneous OLEDs as well as on OLEDs with micro/nano-optical structures is discussed.