PL / Steady-State & Time-Resolved Photoluminescence Spectroscopy

Fluorescence occurs when an orbital electron of a molecule, atom, crystal or nanostructure, relaxes to its ground state by emitting a photon from an excited singlet state:

Excitation: S_o + hv → S₁

Fluorescence: S₁ → S_o + hv

Relaxation from S₁ can occur through interaction with a second molecule/component through fluorescence quenching. In most cases, the emitted light has a longer wavelength, therefore lower energy, than the absorbed radiation (Stokes shift). Molecules/materials that are excited through light absorption or via a different process (e.g. as the product of a reaction) can transfer energy to a second “sensitized” molecule/material, which is converted to its excited state and then fluoresce.

The phenomenon of fluorescence quenching can be examined by time-resolved measurements (TCSPC) in order to distinguish static and dynamic quenching. Further, with TCSPC it is easier to study charge-transfer phenomena from an electron donor to an acceptor material, because the emission quenched states possess different lifetime. The environment of the molecule/material affects both the energy level and the lifetime of the excited state and monitoring these interactions gives essential information about the state of the molecule/material.

μ-PLpower dependence measurement on quantum dot (QD) the excitonic and biexcitonic emission can be easily identified. The FWHM can provide information about the quality the a QD and the distance between the Excitonic and Biexcitonic emission gives information about the binding energy between these two.

Angle-resolved polariton photoluminescence at room temperature conditions shows from the anti-crossing point of the exciton level (dashed line) to exhibit a Rabi splitting as obtained by the simulated lower- and upper-polariton branches (solid curves).