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Photoluminescence (PL)

Photoluminescence (PL)

Steady-State Optical Spectroscopy for Material Analysis

A steady-state optical spectroscopy technique for probing photoluminescence emission and electronic states in materials.
Excitation and emission spectra in steady-state photoluminescence spectroscopy
Table of contents

Decoding Light Emission in Materials

What is Photoluminscence (PL)?

Photoluminescence (PL) is a steady-state optical spectroscopy technique used to study light emission from materials under continuous optical excitation. When photons with sufficient energy promote electrons to higher electronic states, radiative recombination processes emit photons at characteristic energies. The resulting emission spectrum reflects the electronic states and optical transitions of the material. PL is widely applied in materials science, including semiconductor and solar cell research, to evaluate band structure, defect states, and overall material quality.

Example of steady-state emission spectra and time-resolved emission spectra recorded from polymer-based samples, illustrating spectral and temporal photoluminescence analysis.

How does Photoluminscence (PL) work?

In a PL experiment, the sample is illuminated with continuous-wave or pulsed light of energy above its absorption threshold. The absorbed photons excite electrons to higher electronic states, which relax and recombine radiatively, emitting lower-energy photons. The emitted light is spectrally filtered and detected to produce an emission spectrum that reflects the optical transitions within the material. Since PL measurements are performed under steady-state conditions, the technique provides spectral information but does not capture the temporal evolution of emission. To access time-dependent emission dynamics and excited-state lifetimes, photoluminescence can be studied using time-resolved techniques such as Time-Resolved Photoluminescence (TRPL).

EasyTau 2: spectroscopy control and analysis software

PL Data & Analysis

PL data are typically presented as emission spectra showing intensity as a function of wavelength or photon energy. Peak positions provide information on bandgap energies and electronic transitions, while peak shape and linewidth reflect disorder, defect density, and compositional variations. Variations in emission intensity indicate relative radiative efficiency and material quality.

When combined with optical microscopy or spatial scanning, PL measurements can be extended to spatially resolved analysis, commonly referred to as PL imaging or micro-PL. This approach enables mapping of spectral features across a sample to reveal local inhomogeneities, grain boundaries, and defect distributions.

PicoQuant software for PL Imaging analysis

PicoQuant’s EasyTau 2 provides an intuitive software environment for steady-state photoluminescence spectroscopy, enabling rapid visualization, spectral evaluation, and comparison of PL emission data. SymPhoTime 64 extends PL analysis to spatially resolved measurements by combining spectral and imaging workflows for micro-PL and PL imaging experiments within a unified acquisition and analysis platform.

Why use PL?

Photoluminescence provides a non-destructive and highly sensitive probe of optically active electronic states in materials. It enables rapid assessment of band structure, defect-related emission, and material uniformity without the need for electrical contacts or elaborate sample preparation. PL is therefore well suited for characterizing semiconductors, nanomaterials, LEDs and other optoelectronic structures, as well as for monitoring material quality during synthesis and device fabrication.

Schematic overview of the FluoMic add-on showing the dedicated sample mounting unit, pre-aligned fiber connections, and fiber in- and out-coupling modules for integration with optical microscopes. Taken from Ermilov et al., Rev. Sci. Instrum. (2020).

Instrumentation requirements for TRPL

Accurate and reproducible PL measurements require a stable optical excitation source, wavelength-selective detection, and high-sensitivity photon detection. Depending on the application, PL can be performed as point spectroscopy or combined with a microscope for spatially resolved measurements.

For Spectroscopy and Microscopy

Time-Resolved Photoluminescence Course

Intro course on time-resolved photoluminescence, covering methods, instrumentation, and data analysis.
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Matching Applications

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Image of a solar cell surface structure used for optical characterization of charge carrier dynamics and recombination processes.
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Solar Cell Characterization

Time-resolved photoluminescence emission spectrum showing three peaks from different semiconductor layers, illustrating layer-specific recombination dynamics.
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Semiconductor Research

Schematic illustration of nanostructured materials on a substrate highlighting heterogeneous nanoscale architectures studied by optical and time-resolved characterization.
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Application Examples

The following examples demonstrate how steady-state and time-resolved photoluminescence measurements provide spectral and lifetime insight across diverse sample types and spatial scales.

Photoluminescence emission spectra of Fluorescein at different concentrations

Microvolume Fluorescence Spectroscopy of Low-Volume Samples

Steady-state emission spectra and fluorescence lifetimes were measured from low-volume Fluorescein samples down to picomolar concentrations. Emission spectra were compared under different excitation wavelengths, and lifetime decays were evaluated using tail-fit and reconvolution analysis. The results demonstrate reliable spectral and temporal characterization even at extremely low signal levels.

Excitation and emission spectra in steady-state photoluminescence spectroscopy

Steady-State and Time-Resolved Photoluminescence with FluoMic

Steady-state spectra, fluorescence decays, and time-resolved emission spectra (TRES) were recorded from well-defined micrometer-sized regions using a spectrometer–microscope assembly. Polymer standards, structured materials, and display pixels were analyzed to correlate spectral, temporal, and spatial information, enabling localized photophysical characterization beyond conventional bulk spectroscopy.

Photoluminescence spectra of CIGS solar cell at different positions

TRPL Characterization of a CIGS Thin-Film Solar Cell

Steady-state emission spectra and time-resolved photoluminescence decays were acquired from defined regions of a CIGS solar cell using variable objective magnifications. Differences in lifetime behavior between measurement spots revealed spatial variations in recombination dynamics, highlighting the importance of localized excitation and detection areas in semiconductor analysis.

Related Methods

TRPL decay curves showing different lifetimes

Time-Resolved Photoluminescence (TRPL)

A time-resolved spectroscopy technique that records the temporal evolution of photoluminescence emission after pulsed optical excitation. By analyzing the decay of the emitted signal over time, TRPL provides insight into carrier recombination processes and excited-state lifetimes.

Time-resolved photoluminescence image and decay curves of a CIGS solar cell measured using superconducting nanowire single-photon detectors revealing defect-related recombination dynamics.

Time-Resolved Photoluminescence Imaging (TRPL Imaging)

An imaging-based extension of TRPL that combines time-resolved detection with spatial scanning or widefield acquisition. TRPL imaging maps photoluminescence lifetimes across a sample, enabling visualization of local variations in recombination dynamics, defects, and material inhomogeneities that are not accessible with spectroscopic measurements alone.

In-Depth Scientific Resources

Premium Resources

Access in-depth application notes and scientific posters with detailed methods, measurement data, and real-world use cases.

Poster: Photoluminescence Analysis of PV Devices

Poster on non-destructive photoluminescence analysis of PV devices using TRPL microscopy to study carrier dynamics, diffusion and material properties.

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Poster: Photoluminescence Studies

TRPL studies from ps to ms reveal multicolor excitation dynamics and long-lived luminescence processes in advanced materials

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Application Note: Time-Resolved Fluorescence Spectroscopy and Microscopy

How time-resolved fluorescence spectroscopy and microscopy reveal excited-state dynamics, defects, and charge-carrier processes

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Poster: High Spatial Photoluminescence Investigation of Nanostructures

Poster on high-spatial photoluminescence studies of nanostructures and quantum emitters using time-resolved confocal microscopy and spectroscopy.

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Application Note: Measuring Steady-state and Time-Resolved Photoluminescence

Learn how time-resolved fluorescence techniques reveal excited-state dynamics and charge-carrier processes in materials.

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Application Note: Microvolume Fluorescence Spectroscopy Measurements

This application note shows how microvolume fluorescence spectroscopy with the FluoTime 250 enables sensitive lifetime and spectral measurements from minimal sample volumes.

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Poster: Measuring Steady-state and TRPL

Measuring steady-state and TRPL of a thin film CIGS solar cell by a positionable, micrometer-sized observation volume

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Scientific Insights & Resources

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Confocal photoluminescence maps showing spatially localized emission regions in InGaN red InGaN multiple quantum wells.
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