# Understand Phosphorescence

hi

i have still some troubles to understand phosphorescence:

http://en.wikipedia.org/wiki/Phosphorescence" [Broken]

wikipedia has a diagram, where an electron in an exicted state that is a singulet state falls on a second level that is a triplet state.

my problem is, that this first transition is explained by spin-orbit coupling. but is it no so, that the ground state and this triplet state should have spin-orbit coupling either?- but in this case, the transition from the triplet state to the ground state should also be possible.

so it is possible to have this coupling just between some states?

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does nobody have an idea or is there anything wrong with my question?

DrDu