The reason for the decrease in the brightness of the LEDs has been identified. Free Technical Library News

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Identified the reason for the decrease in the brightness of the LEDs

08.05.2013

Researchers at the University of California at Santa Barbara, in collaboration with colleagues at the Ecole Polytechnique in France, have discovered the reason why LEDs dim dramatically at high currents. This reason turned out to be the Auger recombination effect, in which excess energy is transferred to another electronic excitation.

LEDs have huge potential and could solve many energy and economic problems. Replacing conventional lamps with LEDs across the country could save hundreds of megawatts and make dozens of power stations redundant.

Unfortunately, LEDs are still too expensive for mass use, not least because when a powerful current is applied, they do not glow brighter, but rather become dimmer. Because of this phenomenon, it is impossible to create powerful lamps based on a single ultra-bright LED. As a result, you have to use arrays of LEDs, which naturally cost more and take up more space.

To discover the cause of LED fading, an international team of scientists conducted a complex experiment using a vacuum chamber and a special LED with a surface capable of reading the energy spectrum of the electrons emitted by the LED. The results obtained unambiguously showed that the reason for the decrease in the brightness of LEDs at high currents is energetic electrons, which were formed during Auger recombination. In LEDs based on nitride semiconductors, this process occurs when electrons lose energy in collisions with other electrons, and not light is released, but heat.

Now that scientists know exactly why traditional LEDs don't work at high currents, engineers can create LEDs that don't have this problem. It can be expected that in the coming years there will be LEDs that can take a lot of current and turn it into super-bright light.

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A quantum crystal has been created 18.11.2012

Both precious diamond and cheap graphite are made of the same carbon atoms. A tiny but very important difference between these materials is the geometric configuration of their blocks. The same material cannot be both diamond and graphite at the same time. However, in quantum physics there is no such limitation - this was demonstrated by a team of physicists led by Professor Immanuel Bloch from the Max Planck Institute for Quantum Optics and Ludwig Maximillian from the University of Munich.

The experiments were carried out with an ultra-cooled quantum gas. Under the influence of a laser beam, individual atoms can be ordered into regular geometric structures. But unlike classical crystals, all possible configurations of a quantum crystal will exist simultaneously. This observation was made after the transition of particles into the so-called. Rydberg state, in which they are strongly excited by the energy of the light beam.

"Our experiment demonstrates the potential of Rydberg gases to create new states of matter. Thus, we lay the foundation for quantum modeling, for example, quantum magnets," says Immanuel Bloch.

The experiment began with cooling an ensemble of several hundred rubidium atoms to temperatures close to absolute zero and trapping the atoms in a light trap. Then a periodic light grating was superimposed on the atomic cloud - the so-called. an optical grating providing almost uniform filling in the central part of the atomic trap. Then, using a laser, the atoms were brought to the Rydberg state, in which the outer electron shell is located at a great distance from the nucleus. As a result, the area of influence of these atoms grew by about 10 times to a simply huge size - a few micrometers, about 000/1 of a human hair. Now these atoms began to interact through the so-called. van der Waals forces.

The mutual repulsion of these atoms leads to the fact that they are located at a distance of several micrometers from each other. There is a spatial correlation between atoms, which, depending on the number of excited atoms, leads to different crystal lattice geometries. To be more precise, all possible crystal lattices exist there simultaneously. This new state of matter is very fragile, it exists only as long as the laser beam is on and the atoms are excited.

Taking "instant pictures" of such configurations with a special technique with the highest resolution, scientists have identified various geometries of this crystal. Typical configurations are three atoms in an equilateral triangle, four or five form squares, and regular pentagons. The experiments are in good agreement with the predictions of numerical simulations.

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