PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 1: Synthesis, Characterization and Applications of Gold Nanoparticles
measuring absorption, scattering or emission of light that contains information about
properties of the materials. Commonly used techniques include UV-visible electronic
absorption spectroscopy, photoluminescence, infrared absorption and Raman scattering.
These different techniques can provide different information about the nanoparticle properties
of interest [42].
(i) UV-Visible Spectroscopy
The basic operating principle of electronic absorption spectroscopy is based on the
measurement of light absorption due to electronic transitions in a sample. Since the
wavelength of light required for electronic transitions is typically in the UV and visible
region of the electromagnetic radiation spectrum, electronic absorption spectroscopy is
usually called UV-visible or UV-vis spectroscopy [43]. It is named electronic absorption
spectroscopy because the absorption in the UV-visible regions involves mostly electronic
transitions. The spectrum is characteristic of a given sample and reflects the fundamental
electronic properties of the sample. For nanoparticles, UV-visible spectroscopy provides vital
information of nanoparticles through surface plasmon resonance (SPR) studies. This
absorption strongly depends on the particle size, dielectric medium and chemical
surroundings [44].
(ii) Photoluminescence Spectroscopy
At the fundamental level, the principle underlying photoluminescence (PL) spectroscopy is
very similar to that of electronic absorption spectroscopy. They both involve electronic
transition of initial and final states coupled by the electrical dipole operator. The main
difference is that the transition involved in PL is from a higher energy level or state to a lower
energy level [45]. There is also an important practical difference between the two techniques
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