= Metastable electron
{tag=Selection rule}
A fundamental component of <three-level lasers>.
As mentioned at https://youtu.be/_JOchLyNO_w?t=581 from <video How Lasers Work by Scientized (2017)>, they stay in that state for a long time compared to non <spontaneous emission> of metastable states!
https://phys.libretexts.org/Courses/University_of_California_Davis/UCD%3A_Physics_9HE_-_Modern_Physics/06%3A_Emission_and_Absorption_of_Photons/6.3%3A_Lasers mentions that they are kept in that excited state due to <selection rules>.
This is also one of mechanisms behind <phosphorescence> with <triplet states>.
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