Spontaneous emission luminescent. And there are different forms of luminescence depending on how excited atoms are produced (electroluminescence, chemiluminescence etc.). If the excitation is affected by the absorption of radiation the spontaneous emission is called fluorescence. Sometimes molecules have a metastable level and continue to fluoresce long after the exciting radiation is turned off; this is called phosphorescence. Figurines that glow in the dark are phosphorescent. Lasers start via spontaneous emission, then during continuous operation work by stimulated emission. Spontaneous emission cannot be explained by classical electromagnetic theory and is fundamentally a quantum process. The first person to derive the rate of
Sound amplification by stimulated emission of radiation a p-n transition. It has been mentioned that a quantum well is basically a potential well that confines particles to move in two dimensions instead of three, forcing them to occupy a planar region. In coupled quantum wells there are two possible ways for electrons and holes to be bound into an exciton: indirect exciton and direct exciton. In indirect exciton, electrons and holes are in different quantum wells, in contrast with direct exciton where electrons and holes are located in the same well. In a case where the quantum wells are identical, both levels have a two-fold degeneracy. Direct