Photoemission is divided into two categories: fluorescence and phosphorescence. Emission of a photon from the singlet excited state to the singlet ground state—or between any two levels with the same ...Photoemission is divided into two categories: fluorescence and phosphorescence. Emission of a photon from the singlet excited state to the singlet ground state—or between any two levels with the same spin—is called fluorescence. Emission between a triplet excited state and a singlet ground state—or between any two levels that differ in their respective spin states–is called phosphorescence. Both fluorescence and phosphorescence can be used for qualitative analysis and semi-quantitative analysis.