Title: Near Infrared (NIR) Spectroscopy Instrumentation Paul Geladi
1Near Infrared (NIR) Spectroscopy
InstrumentationPaul Geladi
2Paul Geladi
Head of Research NIRCE Chairperson NIR Nord Unit
of Biomass Technology and Chemistry Swedish
University of Agricultural Sciences UmeƄ Technobot
hnia Vasa paul.geladi _at_ btk.slu.se paul.geladi
_at_ uwasa.fi
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4Content
- Spectroscopy?
- Instrumentation
- Modes of measurement
5Content
- Spectroscopy?
- Instrumentation
- Modes of measurement
6Content
- Spectroscopy?
- Energy levels in atoms, molecules, crystals
- Example IR-NIR calculations
- Related techniques
7Content
- Spectroscopy?
- Energy levels in atoms,molecules, crystals
- Example IR-NIR calculations
- Related techniques
8Spectroscopy
- Interaction of radiation and matter
- Electromagnetic radiation
- Gases, liquids, solids, mixtures
- Heterogeneous materials
9Electromagnetic radiation
Cosmic Gamma Xray UV VIS NIR IR Micro Radio
10Electromagnetic radiation
- Cosmic gt 2500 KeV
- Gamma 10-2500 KeV
- Xray 0.1-100 KeV
- Ultraviolet 10-400 nm
- Visible 400-780 nm
- Near Infrared 780-2500 nm
- Infrared 2500-15000 nm
- Microwave GHz
- Radio MHz-KHz
11Why interaction?
- Photon energy matches some energy level
- E hn
- E hc/l
- Plancks constant ????6.63 10-34
12Some useful constants
- qe 1.60217646210-19 As
- me 9.1093818810-31 Kg
- c 2.99792458108 m/s
- h 6.6260687610-34 Js
- 1 Joule to Electronvolt 6.2415063630940281018
13Units
- Joule (energy)
- Electron volt (KeV)
- Wavelength (nm, mm, mm)
- Inverse cm (cm-1)
- Frequency (GHz,MHz,KHz)
14Content
- Spectroscopy?
- Energy levels in atoms,molecules, crystals
- Example IR-NIR calculations
- Related techniques
15HCl molecule (no true sizes)
electron
Xray
UV,VIS
H
Cl
NIR,IR
UV,VIS
Gamma ray
16Photon-matter interaction
- Atomic nucleus gamma ray
- Inner electron Xray
- Outer electron, chemical single bond UV
- Chemical double, triple bond UV,VIS
- Molecular vibration overtone NIR
- Molecular vibration IR
- Molecular rotation Micro
17E
Quantized energy levels
First excited level
hn
Ground level
18What can be measured?
- Emission
- Absorption
- Fluorescence
19E
Emission
First excited level
Thermal
hn????
Ground level
20E
Absorption
First excited level
Thermal
hn???
Ground level
21E
Fluorescence
First excited level
hn???
hn out
Ground level
22Techniques?
- Gamma spectrometry
- Instrumental neutron activation analysis
- Xray spectrometry
- UV-VIS spectrometry (AES,AAS,ICP...)
- NIR spectrometry
- IR spectrometry
- Raman spectrometry
- Microwave spectrometry
23What can be used?
Intensity
Position
Intensity, integral
Width
Energy
24Special topics
- Polarization
- Time resolved spectroscopy
25Content
- Spectroscopy?
- Energy levels in atoms,molecules, crystals
- Example IR-NIR calculations
- Related techniques
26Vibrational spectroscopy
27Morse curves
- The Morse curve describes the potential energy V
of a diatomic molecule as a function of
interatomic distance x. - V De 1-exp(-bx)2
28De 5 b 0.5
29- If the atoms go far apart the bond breaks.
- It is impossible to press the atoms close
together. Enormous amounts of energy are needed.
30De 10 b 0.4
Zero equilibrium distance
31F Fundamental O1 First overtone O2 Second overtone
Quantum levels discrete
O2
O1
F
32This was diatomic molecules
- Polyatomic molecules
- M3N-6 quantized vibration modes
- M3N-5 linear molecules (N1)
- N3 , M3 H2O, H2S, SO2
- N4 , M6 etc
33Triatomic molecules
- G(a,b,c)v1(a1/2) v2(b1/2) v3(c1/2)
- Energy levels
- abc0 (0,0,0)
- a1 bc0 (1,0,0)
- a2 bc0 (2,0,0)
- a0 b1 c0 etc (0,1,0)
34Hot band
Overtone
Combination band
(0,0,2)
Fundamental
(0,2,0)
(0,0,1)
(2,0,0)
(0,1,0)
(1,0,0)
(0,0,0)
Ground level
a
c
b
35Intensity
- Some transitions are more probable
- Gives more intense bands
- Fundamentals in Gas phase
- Overtones in liquid,solid
- Combination bands in liquid, solid
36Hot bands
- Only exist because of thermal excitation
- Boltzmann
- Ne No exp(-DE/kT)
- Ne number excited, No number ground
- k Boltzmann constant 1.380650310-23 J/K
- DE energy difference
37Why cm-1?
38S02
- wavenumber band
- 519 v2
- 606 v1-v2
- 1151 v1
- 1361 v3
- 1871 v2v3
- 2296 2v1
- 2499 v1v3
39Thermal radiation
- Plancks law
- W(l) c1l-5exp(c2l-1 T-1)-1
- T K
- c1 1.9110-12
- c2 1.438104
- ?l mm
40Radiance
4000 K (Tungsten melts)
3500 K
3000 K
2500 K
2000 K
mm
41Planck curves
- More total energy for high temperature
- More UV for high temperature
- More flat curve for low temperature
42Content
- Spectroscopy?
- Energy levels in atoms,molecules, crystals
- Example IR-NIR calculations
- Related techniques
43Energy supply
- Photon
- Thermal
- Electron -
- Proton
- Ion -
44Optics
- Electron optics
- Ion optics
45Techniques
- Electron microscopy
- Electron spectroscopy
- Mass spectrometry
- Ion microscopy
46Transmission
Mono- chromator
Detector
Readout electronics
Radiation source
Sample cell
47Transmission
Mono- chromator
I0
It
Detector
Readout electronics
Radiation source
Sample cell
48Lambert-Beer-Bouguer lawTransmissionAbsorbance
T It / I0 A log10 ( I0 / It) -log10 (It /
I0)
49Lambert-Beer-Bouguer law
A klC l path length k constant C
concentration
50Reflection
Mono- chromator
Detector(s)
Readout electronics
Radiation source
Sample cell
51Reflection
Mono- chromator
Detector(s)
I0
Ir
Readout electronics
Radiation source
Sample cell
52Lambert-Beer-Bouguer lawReflectionPseudoabsorba
nce
R Ir / I0 A -log10 (Ir / I0)
53Content
- Spectroscopy?
- Instrumentation
- Modes of measurement
54What can be changed?
- Radiation source
- Monochromator
- Sample cell
- Detector
55Radiation source
- Tungsten-halogen lamp (Car type)
- Coated tungsten SiC
- Laser(s)
- LEDs
- LED arrays
56ln(Energy flux)
3000K
1000K
0.2
1
ln(Wavelength), mm
571300
Energy flux
LEDs
1000
1150
1520
Wavelength, ?m
58What can be changed?
- Radiation source
- Monochromator
- Sample cell
- Detector
59Monochromator
- Glass filter
- Interference filters
- Prism
- Grating
- Interferometer
- Electrooptical
60Monochromator
- Glass filter not selective
- Interference filters
- Prism too primitive, never used
- Grating
- Interferometer
- Electrooptical
61Interference filter
Low RI coating
Glass
Multiple reflections
High RI coating
62Tilting interference filter
Low RI coating
Glass
Different pathlengths
High RI coating
63There are also gradual interference filters
- Disk with increasing thickness
- Rotate for new wavelength bands
64Filter wheel
Filter wheel
Detector(s)
Readout electronics
Radiation source
Sample cell
65Grating
Pathlength difference
Mirror staircase
66Grating
Exit slit
Entrance slit
Monochromatic
Polychromatic
Rotate
67Interferometer
Fixed mirror
Semitransparant mirror (50)
Moving mirror
Sample
Detector
68Interferometer
Fixed mirror
a
Semitransparant mirror (50)
Moving mirror
b
Wavelengths for which b-a whole cycle
reach detector
Detector (interferogram)
69Interferometer
Interferogram Fourier transform Spectrum
70What can be changed?
- Radiation source
- Monochromator
- Sample cell
- Detector
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72Content
- Spectroscopy?
- Instrumentation
- Modes of measurement
73Modes of measurement
- This is a real strong point of NIR spectroscopy.
There are many modes of measurement - Transmission
- Diffuse reflection
- Fiber optic based
- -Transflection
- -Interaction
74Det
Det
Integrating sphere
Det
Mirror
75Transflectance probe
Fiber bundle
Sapphire mirror
76Mixed solutions
- Use tunable laser instead of monochromator (more
lasers?) - Use LEDs in different wavelengths instead of
monochromator - Use array of detectors instead of scanning
monochromator - DIODE ARRAY
77Grating
Entrance slit
Diode array
Polychromatic
78Filter wheel instrument with interference filters
79Interferometric instrument
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81Process NIR spectrometer based on moving grating
82Transmision instrument
83Sample changer for seeds (transmission)
84Diffuse reflectance instrument (rotating cup)