Plants do not produce silver (or any other metal) nanoparticles. They act as reducing agents for precursors such as ammoniacal silver nitrate. SPR gives rise to the characteristic peaks in the UV-VIS part of the spectrum (and thus to the color of the colloid/sol).

thank you...but how one can understand SPR Phenomenon here how these peaks are created in this range what is the exact cause?

Google (and Wikipedia) is your friend:

https://en.wikipedia.org/wiki/Surface_plasmon_resonance

In addition to Alan F Rawle .

The good explanations of SPR phenomen is presented in paper https://doi.org/10.1070/RC2008v077n03ABEH003751, some details are in our work too (https://doi.org/10.1201/b16895).

At the same time, the papers published by Dr. Naznin A. Begum (see https://www.researchgate.net/profile/Naznin_A_Begum) will be helpful for You. See, for example DOI:10.1007/s40097-016-0209-y; DOI:10.1016/j.ecoenv.2017.09.002.

Good luck!

Liliya

thank you mam

What ever way you prepare silver nanoparticles. It will provide localized surface plasmon resonance as you take it UV-Vis spectrum. These nanoparticles resonate once the plasmon frequency of silver nanoparticles coincide with the frequency of electromagnetic radiation. Location of resonance in the spectrum depends on the shape and sizes of the nanoparticles. Detail information about Plasmonics can be obtained from the books or papers available on google.