Luce a costo zero - il contributo ecologico della fotoluminescenza [Light at no cost - the ecological contribution of photoluminescence]

To talk about photoluminescence, we must first introduce the concept of luminescence; this can be defined as the process by which a substance absorbs energy and then spontaneously emits radiation in the visible field. Light or thermal energy excites the electrons of a luminescent material by passing them from the valence band to the conduction band, where they are confined. Electrons or photons can carry the incoming energy source. Electrons excited during luminescence fall to the lowest energy levels. In some cases, exciting electrons may recombine with gaps. If the emission occurs within 10S of excitation, the luminescence is called fluorescence (instantaneous decay), while if it occurs after 10S, we speak of phosphorescence (decay that continues even after ceasing to irradiate the sample).