Monophotonic and Multiphotonic Processes

There are two distinct ways in which a biphotonic process can take place. 

The emission of delayed fluorescence through triplet-triplet annihilation (see section 3.4.2) can be taken as an example of this type of biphotonic process. 

Biphotonic processes depend greatly on light intensity, and on the lifetimes of the excited states M. Their importance increases markedly in conditions of very intense, pulsed light excitation, e.g. in laser beams or in flash light. 

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