Organic light-emitting diodes radiate white
The search for energy-saving light sources is increasingly moving away from traditional light bulbs, which produce more heat than light. Silicon-based light-emitting diodes have already taken on the role of light source in flashlights, car taillights and portable projectors. However, the future could belong to even more efficient organic light-emitting diodes (OLEDs).
A team of scientists led by Stephen Forrest from the University of Michigan has now presented a new type of OLED. In it, three dyes are excited electrically and emit red, blue and green light when they transition to the ground state, which adds up to white light. In contrast to previous models, this does not happen with all three color molecules through phosphorescence, but with the blue dye through the related fluorescence. The difference between the processes is on a quantum physical level: While in fluorescence an electron is energetically increased and falls back to its original level, in phosphorescence it also has to change its spin.
The new principle avoids energy losses that inevitably occur with purely phosphorescent OLEDs and thus achieves around twenty percent higher energy efficiency. Compared to conventional incandescent lamps, the yield increase is even 50 to 75 percent. Since the service life has also been improved compared to previous OLEDs, organic light-emitting diodes based on fluorescence-phosphorescence could finally be ready for the market, the researchers write.
