A significant fraction of light generated within an organic light emitting diode (OLED) is often trapped within the
structure within waveguide modes and is unable to escape usefully from the device. Addressing this issue is of
significant importance, as it potentially offers a route to improve the external efficiency of OLEDs. Here, we discuss a
number of methods to improve light extraction efficiency from conjugated-polymer LEDs. Firstly we explore the use of
low finesse optical microcavities to redistribute trapped-light into externally propagating modes. The improvements
obtained by simply adopting a microcavity structure on its own are rather small, however we then show that they can be
improved significantly by improving the reflectivity of the cathode. Finally, we show that by engineering a photonic
crystal beneath the anode of a polymer LED, a significant improvement in external efficiency (by a factor of 2) can be
achieved. Such an approach is anticipated to be readily scalable to a manufacturing environment.
Non-linear carrier-photon dynamics are studied for optically pumped InAs quantum dot (QD) laser structures, using excitation into the GaAs barrier by two degenerate pump and probe laser pulses. The non-linear emission from QDs excited by the pump pulse is further amplified by the probe excitation. By varying the delay between the two pulses a very fast decay of the QD excited state emission is measured. Notably slower dynamics for the QD ground state are observed, governed by state filling phenomena, which result in gain saturation.