Could you please be more specific?  The most common definition for PET I know is positron emission tomography.  This is a nuclear decay, rather than a fluorescent process.

Dear David,

Thanks for your answer.

PET: Photoinduced Electron Transfer. its a fluorescence phenomena.

Have a good day!

The lifetimes will typically be in the single ns, however they are dependent on the probe and the probe environment (if the probe is in the "pocket" of a protein

Dear Dr. Thoma....

I think so, that the lifetime will be long (ns).

Thanks for your answer.

Have a good day!

Bye!

PG