The May (2015) issue of Nature Materials contains a ‘focus on LED technology‘, surely motivated by the UNESCO International Year of Light 2015 and the Nobel Prize in Physics 2014 acknowledging the discovery of highly efficient blue gallium nitride (GaN) light-emitting diodes (LEDs). The latter actually set the basis for the current revolution in lighting technology we all witness.
But there is more than just LEDs made from inorganic semiconductors like GaN (an more complex GaN-based ternary alloys), which produces white light when paired with downconversion phosphor materials. LEDs made from organic semiconductors (OLEDs) or quantum dots (QD-LEDs) are alternative, high efficiency device concepts that offer to participate in the transition to an all solid-state light source future. I got a chance to comment on both technologies in the above mentioned Nature Materials focus (Complementary LED technologies). With respect to all major LED technologies (LED, OLED, and QD-LED), if there is one thing that I wish we will see in future is the coexistence of all different concepts, where each application is further advanced by the most suitable architecture.
Starting May 2014, I took a position as Juniorprofessor (Assistant Professor) for Organic Semiconductors at the Institut für Angewandte Photophysik, Technische Universität Dresden, Germany. I am looking forward to to build up my own research group to follow up on various ideas that I bring in my backpack.
A new paper was just published in Applied Physics Letters entitled ‘High efficiency, dual emission from an organic semiconductor‘. The work describes the observation of highly efficient luminescence of both singlet and triplet states of a purely organic semiconductor, namely N,N’-bis(4-benzoyl-phenyl)-N,N’-diphenyl-benzidine, at room temperature. This unusual observation is the result of a very effective suppression of non-radiative modes within the triplet manifold of the molecule, enabling high efficiency phosphorescence. Together with efficient fluorescence, this molecule transforms in a dual state emitter, a phenomenon we term ‘biluminescence’. As neither singlet nor triplet states are a loss channel in the emitter molecule, the mixing between the two states through intersystem crossing (ISC) and back (reverse ISC) only dictates the relative intensities of fluorescence and phosphorescence. An biluminescence emitter may find future applications as ultra broadband emitters, exciton probes, various types of sensors, and spin independent energy transfer intermediates.