Optical Spectroscopy with dispersive Spectrometers
Basics - Building Blocks - Systems - Applications

This page summarizes chapter 4 of the book
"Applications of Dispersive Optical Spectroscopy Systems",
ISBN 9781628413724, SPIE monographs, Bellingham, WA, USA

Applications – L1
Luminescence, static

(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.

L1.0 Introduction

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 sample
spontaneus
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.

Jablonski diagram and typical Luminescence Spectra
Graph L1:
The Jablonski diagram

L1.0.1 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.

L1.0.3 Setup of a static Fluorescence Spectro Photometer
With regard to the above requirements 1 through 5, the following high performance setup results: 
Researchj Grade Luminescence Setup
Graph L2
shows a lens coupled system setup
L1.0.3.1 The Light Path and spectral Disturbance
L1.0.4 Details of a static Photo Luminescence Spectro Photometer
L1.0.4.1
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:
 
Excitation curves at the example  Rhodamin-Bl
Graph L3:
the most important spectra
in the excitation arm, demonstrated by Rhodamin-B
L1.0.4.2 Creation of the Reference Signal
L1.0.4.3 Why to apply a double Monochromator in the excitation Branch?
L1.0.4.4 Illumination of the Sample

Different Sample Geometries
Graph L4A:
The most popular sample geometries and illumination modes.

 
Orientation of the Measurement Beam
Graph L4B:
Beam orientation: vertical versus horizontal
L1.0.4.5 The Emission Light Pass

 F/2 vs F/4 Sample Compartment

Graph L5: Comparison of collection with f/2 versus f/4 apertures
L1.0.4.6 Spectral Dispersion and Processing of the luminescent Light
 Resolution Examples at Ovalen
Graph L6
: impact of the system bandwidth, combined with the kind of data acquisition.
L1.0.5 Measurement Methods for Luminescence Spectroscopy
L1.0.5.1 The Emission Scan

L1.0.5.2 The Excitation Scan
L1.0.5.3 Fluorescence Polarization

The equations:
F39, the sample polarization (the degree of polarizations):  
P = [(Ip – Is) / [(Ip + Is)]
F40, the anisotropy   r = [(Ip – Is) / [(Ip + 2Is)]
L 1.0.5.4 Acquisition of the total Fluorescence

 3D-Plot

Graph L7
: the total luminescence displayed in 3-D mode
L 1.0.5.5 Fluorescence Resonance Energy Transfer, abbreviated FRET, also called Förster Energy Transfer
L 1.0.5.7 Two-Photon Excitation/Upward Luminescence
 

Jablonksi diagram for upwrd conversion
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
The detector

L1.0.9 Calibration, Comparison of Systems, and Stray Light Testing
L1.0.9.1 Calibration
L1.0.9.2  Comparison of Luminescence Systems and Performance Test
The graphical explanation of the
Raman S/N-R measurement is like that:
Raman at Water
Graph L9
: the signals required to calculate the Raman S/N-R measurement at water
L1.0.9.3 Scattering Light /False Light Test in the Excitation
L1.0.9.4 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.

L1.0.10 Example of a research grade System
Foto of a Complete System
Photo L
10
displays a system, fulfilling all requirements of L1.0.7 above
 

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