1. Spectrophotometers measure the intensity of transmitted radiation as a function of wavelength and have five key components: a radiation source, wavelength selector, sample holder, detector, and readout system. 2. Absorption spectrometers use an external radiation source, while emission spectrometers use the sample itself as the radiation source. 3. Common radiation sources include tungsten lamps for visible light, deuterium lamps for ultraviolet light, and heated filaments or globars for infrared light.

1. UNIT THREE
Instruments For Optical Spectroscopy
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INSTRUMENTS FOR OPTICAL SPECTROSCOPY
UNIT THREE

2. INTRODUCTION
 Spectrophotometer is an optical instrument for measuring
the relative intensity of transmitted radiation.
 Measurement can be done based on the quantity of
transmitted radiation as function of selected wavelength
of the spectral range.
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3. Components of Optical Instruments
 Five components of optical instruments:
1.Radiation source
2.Wave length selector
3.Sample holder
4.Detector
5.Readout System
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4. Absorption spectrophotometer
Fig: block diagram of a single beam absorption spectrometer
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5. Fig: block diagram of a single beam Emission spectrometer
• Does not need an external radiation source
• the sample it self is the emitter
• the sample container is an arc, a spark or flame.
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Emission spectrometer

6. 1.Raiation source
Requirements:
1.The source must emit continuous radiation over the entire
wavelength range
2.The intensity of the radiation over the entire wavelength range
should be high and should not vary in intensity.
3.The intensity of the radiation should not fluctuate over long
and short period (its out put should be stable).
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7. 7
1.Tungsten Lamp:visible light (320-2500 nm)
-Low pressure
2.Deuterium Lamp:ultraviolet Light (160-375 nm)
Tungsten Filament
- based on black body radiation:
heat solid filament to glowing, light emitted
will be characteristic of temperature more
than nature of solid filament,
40V ElectricArc
Electrode
Filament
D orH Gas
2 2
Sealed QuartzT
ube
In presence of arc, some of the electrical energy
is absorbed by D2 (or H2) which results in the
disassociation of the gas and release of light
D2 + Eelect  D*
2  D’ + D’’ + hn (light produced)
Excited state
Quartz windows must be used in the tubes, since glass
absorbs strongly at this wavelength region.
Uv-Vis Radiation Source

8. IR Radiation source
 Infrared radiation can be produced by electrically heating a source,
often a Nernst filament or a Globar to 1000-1800 C.
a. Nernst filament
 is fabricated from oxides of zirconium, thorium,Yitrium, and
cerium.
 it works in the range of 500 to 25,000 cm-1
b. The Globar
 is a small rod of silicon carbide
 It works in the range of 250 to 10,000 cm-1
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9. 2. Wavelength selector
 disperse polychromatic radiation into a restricted wavelength
region.
 The most common device used for this purpose called a
monochromator.
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Block diagram of wave length selector

10. Contd.
 Prism:
 Filter:
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11. Contd.
 The prism is used to disperse UV, visible and IR
 The prim is made up of :
 IR- NaCl, KBr, CaF2
 UV- Silica or quartz
 Visible- glass
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12. 3. Sample Cell
- cuvette
- Made of material that does not absorb light in the wavelength
range of interest.
1. Glass – visible region
2. Quartz – ultraviolet
3. NaCl, KBr – Infrared region
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13. 3.Radiation Detector
 Radiation detector is the device that measures the amount
of light passing through the sample.
 convert the radiation energy into electrical energy
 The electrical signal produced by the detector should be
directly proportional to the intensity of the beam of
radiation striking the detector.
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