Encyclopedia > letter P > photoluminescence

Photoluminescence

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Acronym: PL

Definition: emission of light which is caused by the irradiation of a material with other light

More general term: luminescence

Category: article belongs to category physical foundations physical foundations

DOI: 10.61835/jld Cite the article: BibTex plain text HTML Link to this page! LinkedIn

Photoluminescence is the emission of light which is caused by the irradiation of a substance with other light. The term embraces both fluorescence and phosphorescence, which differ in the time after irradiation over which the luminescence occurs. The radiated light is often visible, but can also be in the ultraviolet or infrared spectral region.

Physical Basis

Photoluminescence in semiconductors and dielectrics can usually only occur for illumination of a substance with light which has a photon energy above the band gap energy. (Exceptions are cases with multiphoton absorption at high optical intensities.) The photoluminescence usually occurs for wavelengths around the band gap wavelength.

In many cases, photoluminescence occurs only with certain dopants or impurities in a material. For example, fluorescence can occur when rare-earth-doped laser gain media are pumped with light which can excite the rare earth ions. Here, the emission can occur in various wavelength bands corresponding to optical transitions of those ions. One may obtain more than one photon per absorbed photon, when there is a cascade of transitions.

Photoluminescence may be largely suppressed (quenched) if there are fast non-radiative transitions to lower energy levels, leading to a very small lifetime of the excited levels..

Photoluminescence for the Characterization of Photonic Devices

Photoluminescence is sometimes used for the characterization of photonic devices or parts thereof. For example, one may irradiate a semiconductor wafer, on which additional layers for a semiconductor laser or a saturable absorber have been fabricated, with short-wavelength light for exciting photoluminescence. The optical spectrum of the photoluminescence (PL spectrum) and also the dependence of its intensity on the irradiation intensity and device temperature can deliver important information for device characterization. In particular, PL spectra and their intensity dependencies can allow one

to determine the band gap energy
to estimate the wavelength of maximum gain
to determine the composition of ternary or quaternary layers
to determine impurity levels (which can e.g. lead to the emission of light with longer wavelengths than otherwise possible)
to investigate recombination mechanisms

Photoluminescence mappers (PL mappers) can spatially resolve the photoluminescence, e.g. from epitaxially grown wafers. PL maps can reveal, e.g., a radial dependency of layer thickness or material composition.

Note that the characterization of photoluminescence is possible before any electrodes if been applied to the semiconductor structure.

More to Learn

Fluorescence

Questions and Comments from Users

Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.

Please do not enter personal data here. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via e-mail.

By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.