UV spectroscopy

1. UV SPECTROSCOPY IN
NANOMATERIALS
-17PHY212
Mahesh Mishra
-17PHY213
Rakesh Solanki
-17PHY215
Swapnil Agnihotri

2. INDEX
 Introduction
 Principle
 Beer-Lambert Law
 Spectroscopic Process
 Conclusion
 Difference in nanomaterials
 Applications
 Limitations

3. Introduction
 UV spectroscopy is the measurement of the attenuation of
a beam of light after it passes through a sample or after
reflection from a sample surface.
Absorption measurements can be at a single wavelength
or over an extended spectral range.
 The ultraviolet region falls in the range between 190-
380 nm, the visible region fall between 380-750 nm.

4. Principle
 UV absorption spectra arise from transition of electron within a
molecule from a lower energy level to a higher energy level.
 A molecule absorb UV radiation of frequency (𝜗), the electron in
that molecule undergo transition from lower to higher energy
level.
 The energy can be calculated by the equation,
E=h𝜗

5. Transition

6. Beer-Lambert Law
 The Beer-Lambert law states that the quantity of light
absorbed by a substance dissolved in a fully transmitting
solvent is directly proportional to the concentration of the
substance ,the path length of the light through the solution
and the intensity of incident light.
 The expression of Beer-Lambert law is-
A = log (I0/I) = ɛCL.

From the Beer-Lambert law it is clear that greater the
number of molecules capable of absorbing light of a given
wavelength, the greater the extent of light absorption.

7. Beer-Lambert Law
 If the band of wavelength selected on the spectrometer is such that the
molar absorptivities (ɛ) of the analyte is essentially constant, deviations
from Beer-Lambert law are minimal.
 However, if a band is chosen such that the molar absorptivity of the
analyte at these wavelengths changes a lot, the absorbance of the
analyte will not follow Beer-Lambert law.
 It is observed that the deviations in absorbance over wavelengths is
minimal when the wavelength observed is at the λmax. Due to this
reason absorption measurements are taken at wavelengths.

8. Deviation
It is often assumed that Beer’s Law is always a linear
plot describing the relationship between absorbance and
concentration.
Deviations do occur and cause non-linearity. This can
be attributed to a range of chemical and instrumental
factors.

9. Instrumentation

10. Spectroscopic Process
 In UV spectroscopy, the sample is irradiated with the broad
spectrum of the UV radiation.
 If a particular electronic transition matches the energy of a
certain band of UV, it will be absorbed.
 The remaining UV light passes through the sample and is
observed.
 From this residual radiation a spectrum is obtained at
discrete energies. This is called an absorption spectrum.

11. Spectroscopic Process
 A spectrophotometer records the degree of absorption by a
sample at different wavelengths and the resulting plot of
absorbance (A) versus wavelength (λ) is known as a spectrum.
The significant features:
 λmax (wavelength at which there is a maximum absorption).
 єmax (The intensity of maximum absorption)

12. Absorbance Vs Wavelength

13. Absorbance Vs Concentration

14. Difference in Nanomaterials
 Metal nanoparticles exhibit a surface plasmon resonance
i.e. the collective oscillation of electrons in the
conduction band of nanoparticles in resonance with a
specific wavelength of incident light.
 Semiconductor nanoparticles exhibit Quantum
confinement effect
 It is dependent both on the size and shape of gold
nanoparticles. The peak absorbance wavelength
increases with particle diameter, and for uneven shaped
particles , the absorbance spectrum shifts significantly
into the far-red region of the spectrum when compared
to a spherical particle of the same diameter.

15. Difference in Nanomaterials
 Gold nanoparticle size dependant surface plasmon resonance. Note the red-shift of the
absorption maximum as the gold nanoparticle size increases.

16. Difference in Nanomaterials
 Position of LSPR also depends on various factors like depends upon
surrounding,dielectric constant,interparticle seperation.
 As the band gap increases with a decreasing size, resulting in the
interband transition shifting to lower wavelength.
 The absorbance peak varies with time.This is the effect of
agglomeration.

17. Applications
 Detection of functional groups.
 Detection of impurities.
 Qualitative analysis.
 Quantitative analysis.
 Single compound without chromophore.
 Drugs with chromophoric reagent.

18. Limitations

19. References
UV Spectroscopy : Techniques, instrumentation and
data handling- B.J.Clark
https: //www.researchgate.net
 Determination of Size and Concentration of Gold
Nanoparticles from UV−Vis -Spectra-Wolfgang Haiss

20. Thank You