Fluorescent impurity emitter in toluene and its photon emission properties

Single fluorescent emitters like colloidal quantum dots or single molecules are usually prepared in solutions and spin-coated onto cover glasses for studying. Toluene has been a widely used solvent in such studies. Here, we report on a fluorescent impurity emitter contained in toluene and its optical properties. The emission spectra of the single emitters show multiple peaks with the main peak varying from 2.03 eV (610 nm) to 2.14 eV (580 nm) and a red-shifted side peak with an average separation of 167 meV from the main peak. The emitted photons show a strong anti-bunching with a fluorescence lifetime of a few nanoseconds. They show very fast blinking behavior which cannot be properly detected by time-trajectory of photoluminescence intensity. An analysis based on the second-order correlation functions reveals that a three-level model can explain our measurements well and that the blinking transition time ranges only a few tens of microseconds. This single emitter in toluene is clearly distinguished from the fluorescent centers in the cover glass by their respective emission spectra. The single emitters in the cover glass also exhibit fast blinking behavior. These background emitters should be carefully identified and distinguished while studying the single fluorescent emitters.