Optical Spectroscopy with
Basics - Building Blocks - Systems - Applications
summarizes chapter 4 of the book
"Applications of Dispersive Optical Spectroscopy Systems",
ISBN 9781628413724, SPIE monographs, Bellingham, WA, USA
Applications – L1
(Photo)Luminescence - Fluorescence – Phosphorescence
This page presents the directory, the signs and symbols, conversions, and equations of the book, while the details are an exclusive part of the book.
The interaction between light and matter may lead to the following effects:
1) Transmission without interaction, Reflection without absorption effects
2) Transmission/Reflection, where the light changes the energetic state of the samplespontaneus
3) Transmission/Reflection with light scattering effects at the sample
The law of preservation of energy says, that the light transmitted through any sample, plus the sum of reflections by the sample results in the factor 1 of the energy introduced:
T + R = 1
The law does not regard the fact, that transmitted light may be refracted, or diffracted, or scattered by the sample. It also does not take into account, that absorbed energies may appear in the beam as luminescent signals.
Graph L1: The Jablonski diagram
Parameters of Luminescence Measurements
L1.0.2 Requirements of Luminescence Mesurements
1. Requirement: the excitation light in the sample volume shall be well focused, to provide high density. Strong light sources are welcome.
2. Requirement: the excitation light shall be spectrally clean, to make sure, that only the target transition is excited.
3. Requirement: as much emitted light as possible shall be collected and measured.
4. Requirement: In both channels, excitation and emission, a programmable polarizer is of advantage.
5. Requirement: in order to allow normalization, a (calibrated, if possible) reference detection is required in the excitation arm. In order to allow emission normalization, the spectrometer system shall provide the ability of radiometric calibration.
Setup of a
With regard to the above requirements 1 through 5, the following high performance setup results:
Graph L2 shows a lens coupled system setup
L22.214.171.124 The Light Path and spectral Disturbance
L1.0.4 Details of a static Photo Luminescence Spectro Photometer
L126.96.36.199 The Excitation Arm
A typical example on the excitation of the fluorophore Rhodamin-B, which is often used as quantum counter, shows the whole picture:
Graph L3: the most important spectra in the excitation arm, demonstrated by Rhodamin-B
L188.8.131.52 Creation of the Reference Signal
L184.108.40.206 Why to apply a double Monochromator in the excitation Branch?
L220.127.116.11 Illumination of the Sample
Graph L4A: The most popular sample geometries and illumination modes.
Graph L4B: Beam orientation: vertical versus horizontal
L18.104.22.168 The Emission Light Pass
Graph L5: Comparison of collection with f/2 versus f/4 apertures
L22.214.171.124 Spectral Dispersion and Processing of the luminescent Light
Graph L6: impact of the system bandwidth, combined with the kind of data acquisition.
L1.0.5 Measurement Methods for Luminescence Spectroscopy
L126.96.36.199 The Emission Scan
L188.8.131.52 The Excitation Scan
L184.108.40.206 Fluorescence Polarization
F39, the sample polarization (the degree of polarizations): P = [(Ip – Is) / [(Ip + Is)]
F40, the anisotropy r = [(Ip – Is) / [(Ip + 2Is)]
L 220.127.116.11 Acquisition of the total Fluorescence
Graph L7: the total luminescence displayed in 3-D mode
L 18.104.22.168 Fluorescence Resonance Energy Transfer, abbreviated FRET, also called Förster Energy Transfer
L 22.214.171.124 Two-Photon Excitation/Upward Luminescence
Graph L8: the Jablonski model for 2-photon absorption/luminescence
L1.0.6 Modulated Excitation for NIR/IR, and Phosphorescence
L1.0.7 Summary of the requirements for a static Luminescence Spectro Photometer
The light source
The Excitation monochromator
The sample illumination and the sample positioning
The collection of the emitted light
The emission monochromator
Calibration, Comparison of Systems, and Stray Light Testing
L126.96.36.199 Comparison of Luminescence Systems and Performance Test
The graphical explanation of the Raman S/N-R measurement is like that:
Graph L9: the signals required to calculate the Raman S/N-R measurement at water
L188.8.131.52 Scattering Light /False Light Test in the Excitation
L184.108.40.206 Scattering Light /False Light Test in the Emission
A false light test in the emission part requires clean excitation. That is set to any wavelength, and a mirror is placed instead of a sample. Now, with high gain, the emission spectrum is recorded. It will reveal quickly, if unwanted signals appear, and at what spectral position. As an emission spectrometer will respond differently to different input wavelengths, a total-fluorescence-alike measurement is required for the full picture. Even now, not all problems may emerge, because only light of a small band us used for illumination, and crosstalk effects may not appear. Quantification is not possible. To achieve that, standard stray light tests with special filter sets and a white light source are requested.
Example of a research grade System
Photo L10 displays a system, fulfilling all requirements of L1.0.7 above
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Spectroscopy with dispersive Spectrometers
Basics - Building Blocks - Systems - Applications " are reserved by
Wilfried Neumann, D-88171 Weiler-Simmerberg. Status April 2012