Einstein's coefficient of spontaneous emission

Einstein's coefficient of spontaneous emission

[¦īn‚stīnz ‚kō·ə¦fish·ənt əv spän¦tā·nē·əs ə′mish·ən]
(atomic physics)
Proportionality constant governing the rate at which atoms or molecules pass spontaneously from an upper energy state to a lower one by emission of radiation, equal to the number of such transitions per second divided by the number of atoms in the upper state.
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