energy transformation in led
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Answer:A light-emitting diode (LED) that emits more light energy than it consumes in electrical energy has been unveiled by researchers in the US. The device – which has a conventional efficiency of greater than 200% – behaves as a kind of optical heat pump that converts lattice vibrations into infrared photons, cooling its surroundings in the process. The possibility of such a device was first predicted in 1957, but a practical version had proved impossible to create until now. Potential applications of the phenomenon include energy-efficient lighting and cryogenic refrigeration.
The energy of photons emitted by an LED is dictated by the band gap of the semiconductor used – the energy required to make an electron–hole pair. When an electron and hole recombine in a radiative process, a photon carries away the extra energy. The voltage across the LED creates the electron–hole pairs but its value does not affect the photon energy, since the semiconductor’s band gap is a permanent feature of the material.
However, it is possible for the individual emitted photons to have energies that are different to the band gap. The vast majority of electron–hole recombinations actually result in the production of heat, which is absorbed by the semiconductor in the form of quantized lattice vibrations called phonons. These vibrations create a heat reservoir that can then boost the energy of photons produced by radiative recombination. In 1957 Jan Tauc at the Institute of Technical Physics in Prague pointed out that, since this provided a mechanism for radiation to remove heat from a semiconductor lattice, there was no barrier in principle to an LED being more than 100% efficient, in which case it would actually cool its surroundings
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electric energy to light energy and heat enery
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