Dear colleague, ı am studying on localized surface plasmon resonance and ı want to learn what is the main cause of blue shift in lspr experiment also what is the differecens between blue shift and red shift
It is the surrounding medium that determines besides of size and shape the resonance frequency of a particle. In case of metallic particles, the frequency of the LSPR is always red shifted compared to frequency of the plasma frequency. Decrease in size leads to a blue shift (higher frequency) while increase of the dielectric constant of the surrounding medium leads to a red shift (lower frequency). Influence of shape can be very complex and lead to additional resonances (e.g. in case of cubes) and/or dependance of the orientation of the particles (e.g. in cases of ellipsoides). See e.g.
Book In Absorption and Scattering of Light by Small Particles
It is the surrounding medium that determines besides of size and shape the resonance frequency of a particle. In case of metallic particles, the frequency of the LSPR is always red shifted compared to frequency of the plasma frequency. Decrease in size leads to a blue shift (higher frequency) while increase of the dielectric constant of the surrounding medium leads to a red shift (lower frequency). Influence of shape can be very complex and lead to additional resonances (e.g. in case of cubes) and/or dependance of the orientation of the particles (e.g. in cases of ellipsoides). See e.g.
Book In Absorption and Scattering of Light by Small Particles
Dear Gul,
Going by Thomas' answer, surrounding medium determines the red shift and blue shift. As far as size reduction is concerned, on reducing the size of the particles, distance between two valence bands get reduced. This leads to increased frequency of electromagnetic wave emission after being excited by LASER. This is blue shift.
Red shift is when crystal size grows after nucleation and distance between valence band increases. This leads to increase in wavelength of electromagnetic wave emitted after the particle being exited by LASER.
Hello Aytaç,
The two answers provided by Thomas and Abdul are very good. There are also several other factors that you may wish to consider, such as homogeneous and inhomogeneous broadening.
You may find the theory section of a review paper I authored useful (link provided). If you need further information you can look at the references.
Kind regards,
Jules.
Usually the cause of shifts in LSPR which has been explored in an extensive way is change in dielectric constant of surroundings as explained in previous answers. However, there are other physical phenomenon as well which can alter the LSPR position namely interparticle coupling, change in particle size or shape, charging of particles, and change in electron dynamics (lifetimes of electrons). Blue shifts can be usually attributed to lowering of particle size or excess electrons on particle due to charge transfer from surroundings.
Mainly the particle shape and size along with surrounding media decides the LSPR location. Inter particle separation and its interaction also play important role in red or blue shift of LSPR peak. Lot of references are available. But following references may clarify the discussion.
Appl. Opt. 26 2395 (1987)
Appl. Opt. 51 2606 (2012)
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