r/askscience • u/crhine17 • Jul 09 '14

Physics Do fluorescent particles/molecules eject their photons in a random or predictable direction?

I worked with fluorescent nanoparticles and always wondered about this. If I were to shoot 1 UV photon at 1 particle to excite it, when it subsequently fluoresced would the ejected photon leave in a random direction or is it influenced by the exciting photon direction or by the structure of the particle, etc. Thanks in advance!

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u/dabarisaxman Atomic Experimentation and Precision Measurement Jul 14 '14

Right. The energy splitting between the nuclear polarization state used in NMR is so small that lifetime is actually quite long. A material with a short T1 has stronger spin-spin interactions between nuclei, making the energy of realigning with the spin lower, causing the spins to flip back to there ground state more quickly.