The mechanism underlying this phenomenon is not fully understood.[1] It is neither
fluorescence not
phosphorescence.[2][3] In fluorescence, the lifetime of the excited state lasts a few nanoseconds. In phosphorescence, even if the emission lives several seconds, this is due to deexcitation between two electronic states of different
spin multiplicity. Persistent luminescence involves energy traps (such as electron or hole traps) in a material,[4] which are filled during the excitation. Afterward, the stored energy is gradually released to light emitter centers, usually by a fluorescence-like mechanism.
Examples of use
Persistent luminescence materials are mainly used in safety signs, watch dials, decorative objects and toys.[5] They have also been used as nanoprobes in small animal optical imaging.[6]
References
^T. Aitasalo, P. Deren, J. Hölsä, H. Jungner, J.C. Krupa, M. Lastusaari, J. Legendziewicz,
J. Niittykoski, and W. Strek. Persistent luminescence phenomena in materials doped with
rare earth ions. J. Solid State Chem., 171 :114, 2003.
^Q. le Masne de Chermont, C. Chanéac, J. Seguin, F. Pellé, S. Maitrejean, J.P. Jolivet, D. Gourier, M. Bessodes and D. Scherman. Nanoprobes with near-infrared persistent luminescence for in vivo imaging. Proc. Natl Acad. Sci. USA 104 :9266–9271 2007.