Fotoluminescens

Fotoluminescens, or photoluminescence, is the emission of light by a material that has absorbed photons. The process involves electronic transitions: after absorption, excited electrons relax to lower energy levels and emit photons as they return to the ground state. The emitted light often has lower energy than the absorbed light, a phenomenon known as the Stokes shift.

Photoluminescens includes fluorescence and phosphorescence. Fluorescence arises from singlet excited states and typically ceases within about 10 nanoseconds after excitation. Phosphorescence involves triplet states and can persist from microseconds to hours after excitation, due to slower radiative decay and intersystem crossing.

It occurs in a wide range of materials, including organic fluorophores, inorganic phosphors, rare-earth-doped crystals, quantum dots, and color centers in solids. Emission color and efficiency depend on the material, dopants, host matrix, and environment. Quantum yield measures the fraction of absorbed photons emitted as light; lifetime measurements characterize the decay kinetics.

Photoluminescens is used in lighting and displays (phosphor-converted LEDs, OLEDs), bioimaging and sensors, and solar-energy technologies such as luminescent solar concentrators and up/down-conversion devices.

Measurement employs photoluminescence spectroscopy, including emission spectra, excitation spectra, and time-resolved PL. Factors such as temperature, concentration, and quenching effects influence intensity and lifetime.

Prominent examples include Eu3+- and Tb3+-doped hosts, CdSe and perovskite quantum dots, fluorescein and rhodamine dyes, and F-centers in crystals.