Fluorescence, Phosphorescence, and Photoluminescence Spectroscopy

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Fluorescence, phosphorescence, and photoluminescence occur when a sample is excited by absorbing photons and then emits them with a decay time that is characteristic of the sample environment. Fluorescence is a term used by chemists when the absorbing and emitting species is an atom or molecule. Phosphorescence is similar to fluorescence, except that the time between absorption and emission is much longer than in fluorescence. Photoluminescence is the term physicists use to describe the absorption and emission of light by things such as semiconductors and nanotubes. Regardless of the terminology, when samples absorb photons and then emit them at a different wavelength the resultant light can be dispersed by a spectrograph, the spectrum can be detected by a device such as a CCD, and information can be gleaned about the sample.

As illustrated in the diagram at right, fluorescence occurs when a chemical species absorbs a photon and is excited to a singlet electronic excited state, relaxes via non-radiative mechanisms, emits a lower-energy photon, and then transitions to the ground electronic state. In fluorescence, the time between absorption and emission is on the order of nanoseconds. The spectrum of the wavelengths emitted can be used to identify atoms and molecules, as well as to determine chemical structures. The intensity of the photons emitted can be used to determine the concentration of chemical species.

Since absorption is a requirement for the fluorescence process, molecules and functional groups that are strong UV-Vis absorbers can be strong fluorescers. For example, molecules with extended pi-electron systems, including aromatic and conjugated aromatic rings, make excellent fluorescers (known as fluorophores). In biology, fluorophores are attached to molecules such as proteins, are excited, and the resultant fluorescence used to image molecules and cells. Spectral analysis of this fluorescence can give chemical information about biological systems.

 

 

 

A near-infrared fluorescence spectrum of a collection of carbon nanotube
(spectrum courtesy of Dr. Daniel A. Heller, Memorial Sloane Kettering Cancer Center, NY).

Phosphorescence
Phosphorescence is similar to fluorescence except the time between photon absorption and emission is from seconds to hours rather than nanoseconds. Like fluorescence, phosphorescence begins with absorption by a photon and excitation to a singlet electronic state. Via a process called intersystem crossing, the singlet state couples to a triplet electronic excited state, which then gives off a photon and relaxes to the ground electronic state. Singlet-triplet coupling is “forbidden” (which is responsible for the time delay in phosphorescence compared to fluorescence). The amino acid tryptophan phosphoresces, so phosphorescence can be used to study proteins.

Photoluminescence
Photoluminescence is fluorescence as applied to semiconductors and other materials. Dispersing the photoluminescent light to form a spectrum can give information such as the purity of semiconductors and the structure of nanotubes.

PI Picks

Fluorescing samples typically produce enough photons for a standard silicon-based CCD to detect a spectrum. Since fluorescence peaks are inherently broad, high-resolution spectra are not necessarily needed to obtain useful data.

IsoPlane Imaging Spectrographs

  • Eliminates field astigmatism across the entire focal plane, giving spectra with improved spectral resolution AND signal-to-background ratio
  • Produces crisp, detailed images across the entire focal plane

Acton SpectraPro Monochromators & Spectrographs

  • Grating stabilization offers simple calibration
  • Optimized coatings for higher throughput -
  • Interchangeable grating turrets with a wide selection of gratings 

PIXIS CCD Cameras

  • Lifetime vacuum guarantee for worry-free operation
  • Deep cooling without the need for liquid circulators
  • Up to 1000 spectra/sec data acquisition
  • Quantum efficiencies of more than 90% available with Princeton Instruments custom sensor chips

 

Software

LightField 64-bit software - trial download
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ProEM EMCCD Cameras

ProEM EMCCD Cameras

EMCCD cameras for ultra-low light, read noise-limited applications.



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IsoPlane Imaging Spectrographs

IsoPlane Imaging Spectrographs

Award-winning imaging spectrographs with superior performance over Czerny-Turner traditional designs, available with 203 mm and 320 mm focal length designs.



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PIXIS CCD Cameras for Imaging & Spectroscopy

PIXIS CCD Cameras for Imaging & Spectroscopy

PIXIS CCD cameras play a key role in revolutionary research performed in leading labs around the world.



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LightField Scientific Imaging and Spectroscopy Software

LightField Scientific Imaging and Spectroscopy Software

Ground breaking software to control your Princeton Instruments systems. It's like nothing you have ever experienced!



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SpectraPro Spectrometers

SpectraPro Spectrometers

High value, dependable industry standard series of spectrographs and monochromators for a variety of applications.



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PyLoN Cameras for Imaging & Spectroscopy

PyLoN Cameras for Imaging & Spectroscopy

PyLoN high-resolution front-illuminated, back-illuminated, & back-illuminated deep-depletion imaging & spectroscopy CCDs.



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PyLoN-IR Linear InGaAs Camera

PyLoN-IR Linear InGaAs Camera

This InGaAs detector offers 16-bit digitization and leads the industry with the fastest spectral rate and lowest system read noise.



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*New* Sophia Ultra-Low Noise CCD Cameras

*New* Sophia Ultra-Low Noise CCD Cameras

Sophia ultra-low noise cameras for the most demanding low-light applications from astronomy to x-ray.



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Featured Product for Fluorescence, Phosphorescence, and Photoluminescence Spectroscopy

IsoPlane Imaging Spectrographs

IsoPlane Imaging Spectrographs

Award-winning imaging spectrographs with superior performance over Czerny-Turner traditional designs, available with 203 mm and 320 mm focal length designs.


Princeton Instruments