Dear Aiman Shamim

Yes, I agree to Mr. Thomas Mayerhofer. In metallic nanoparticle systems, the collective oscillations of free electrons are confined to a finite volume defined by the particle dimensions. Since the plasmons of nanoparticles are localized rather than propagating, they are known as localized surface plasmon resonances (LSPRs). When the free electrons in a metallic nanostructure are driven by the incident electric field to collectively oscillate at a certain resonant frequency, the incident light is absorbed by the nanoparticles. Some of these photons will be released with the same frequency and energy in all directions, which is known as the process of scattering. Meanwhile, some of these photons will be converted into phonons or vibrations of the lattice, which is referred to as absorption. Therefore, LSPRs manifest themselves as a combined effect of scattering and absorption in the optical extinction spectra. 

In other hand, in UV-Vis Spectra, the peaks or div shows the absorption of radiation in the UV-Vis region of the electromagnetic spectrum arises from electronics transition from bound states (outer valence orbitals) to excited electron states. The wavelength limit for this region are 200 to 400 nm for the visible.

For more detail, you can get the information from books below:

1. UV-VIS and Photoluminescence Spectroscopy for Nanomaterials Characterization by  Challa S.S.R. Kumar.

2. Handbook of Nanoscale Optics and Electronics edited by Gary P. Wiederrcht.

The LSPR peak is caused by a collective oscillation of free electrons and the particular shape and size of the metallic particle. In particular a metall does not have a corresponding peak in the imaginary part of the optical constants/dielectric function. In contrast, in a dielectric material usually an electronic excitation of a bound or non-bonding electron causes such a peak which "reflects" itself in the absorption.

Dear Aiman Shamim

Yes, I agree to Mr. Thomas Mayerhofer. In metallic nanoparticle systems, the collective oscillations of free electrons are confined to a finite volume defined by the particle dimensions. Since the plasmons of nanoparticles are localized rather than propagating, they are known as localized surface plasmon resonances (LSPRs). When the free electrons in a metallic nanostructure are driven by the incident electric field to collectively oscillate at a certain resonant frequency, the incident light is absorbed by the nanoparticles. Some of these photons will be released with the same frequency and energy in all directions, which is known as the process of scattering. Meanwhile, some of these photons will be converted into phonons or vibrations of the lattice, which is referred to as absorption. Therefore, LSPRs manifest themselves as a combined effect of scattering and absorption in the optical extinction spectra. 

In other hand, in UV-Vis Spectra, the peaks or div shows the absorption of radiation in the UV-Vis region of the electromagnetic spectrum arises from electronics transition from bound states (outer valence orbitals) to excited electron states. The wavelength limit for this region are 200 to 400 nm for the visible.

For more detail, you can get the information from books below:

1. UV-VIS and Photoluminescence Spectroscopy for Nanomaterials Characterization by  Challa S.S.R. Kumar.

2. Handbook of Nanoscale Optics and Electronics edited by Gary P. Wiederrcht.

A peak in UV absorption spectra is obtained when an electron from a HOMO level absorbs appropriate energy, jumps and goes into higher unfilled shells. Certain selection rules must be satisfied for this process to occur. Resonance condition must be satisfied and Transition Dipole Moment (TDM) should be nonzero for such a transition to be allowed.

A LSPR band is obtained in metal nanoparticles due to collective oscillations of free electrons. Free electrons have a natural frequency of oscillation and when this matches the frequency of incident radiation, absorption of incident light occurs leading to a LSPR band.

do iron nano particles or iron oxide nanoparticle also posses this LSPR peak

In case of iron the effect is very weak. As soon your material is no longer a conductor like iron oxide it completely vanishes.

Dear Sir Thomas, thank you for such nice explanation...

In both the cases absorption of energy is involved. In normal absorption process electrons from the atoms or molecules goes to its excited state, which is observed as absorption peak at certain wavelength. But in the case of LSPR free electrons oscillates in the electric field of light. When the frequency of light matches with the plasma frequency (depends on electron density) then a resonance takes place. This resonance is observed as an absorption peak in the spectra.