Characterization of the radiation properties of quantum dots from the radiation field of an LED

A complete simulation of the radiation pattern generated by an LED requires knowledge not only about the passive optical properties of the stack, e.g., layer thicknesses and refractive indices, but also about its active optical properties, i.e., the profile of the emission zone, the orientation distribution of the emitting ensemble and the internal quantum efficiency. We present a complete characterization of the radiation properties of bottom emitting LEDs, whose emitter is a spin-coated layer of CdSe/ZnS Quantum Dots (QDs) with peak emission wavelength around 628 nm. The passive optical properties have been analysed by standard spectral reflection and transmission measurements combined with ellipsometry. The active properties of the LED have been accessed by analysing the emission pattern of purposely designed devices, in which the light emitted from the QDs interferes destructively with the light reflected from the cathode. Such an interference enables to extract deeper information about the emission zone profile and the orientation distribution of the transition dipole moments, which cannot be accessed in standard devices optimized for maximum external efficiency.