On the Trail of the Mysterious Dark Exciton Matter
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Today LEDs are built into smartphones, televisions, and lamps, and everyday life is unimaginable without them. Their widespread use was only made possible by the development of the blue light-emitting diode, for which the 2014 Nobel Prize in Physics was awarded. Before that, there already were red and green light-emitting diodes. With the advent of the blue light-emitting diode, it now became possible to generate white light too.
To generate light, negative and positive electrical charges are injected into a crystal. When two meet, they transform into light and disintegrate. Before that, they enter into a bound state. This state corresponds to a new particle called an exciton. Excitons can only have certain energies that are specified by quantum mechanics. Each light-emitting crystal exhibits a specific series of exciton energy states, the values of which depend on the material. If you want to optimize this, you need to draw conclusions about the excitons and their characteristic energies. Excitons were first detected in the material cuprous oxide (Cu2O).
Bright and Dark Excitons
Besides the bright, light-emitting excitons, there are also dark excitons that cannot decay into light. Through a quantum mechanical interaction, the so-called exchange interaction, their energies differ from those of the bright excitons. Up to now, in all known materials, including cuprous oxide, only the lowest ground state of this dark exciton matter could be observed. In keeping with their name, these states had previously remained dark and hidden.