The change of colour is mainly determined by the formation of nanoparticles of metals (Au, Ag, etc). It is basically related to the surface plasmon effect, and change in electronic structure (mainly the bandgap). Generally, for the case of silver, when nanoparticles form, they change colour from transparent solution to yellow colour. I guess the synthesis conditions (parameters like temperature sintering, etc) is not properly taken care of. In the case of the chemical synthesis steps, cleaning is the most important factor. Making silver nanoparticles are well optimized up to the commercial level. The good point is you have silver nitrate as raw material. You can adopt another synthesis method. If you wish, I can send my method to make silver nanoparticles, they are highly reproducible and can be prepared using silver nitrate.

Colour does not change of prepared sample (nanoparticles confirmed after XRD and UV) from yellow colour to any other colour means the silver nanoparticles are highly stable. If colour change means either crystallite size increasing or it is forming some other phase or degradation of the prepared sample occurred.

Good luck.

Dear Mohammad, there are very many useful literature references about various synthetic routes to silver nanoparticles available right here on RG. Just search for terms like "synthesis of silver nanoparticles" and then click on "Publications". As a typical example please have a look at the following useful article:

Green synthesis of silver nanoparticles using Croton sparsiflorus morong leaf extract and their antibacterial and antifungal activities

Article Green synthesis of silver nanoparticles using Croton sparsif...

This paper (and many others) is freely available as public full text on RG. The color of Ag NPs is normally described as gray, yellow, yellow-brown or brown.

Good luck with your work!

Dear all, the color of AgNP's may be an artifact related to the synthesis protocols. Please have a look at the following document. My Regards

https://doi.org/10.1039/C6RA08336F

It is necessary analysis by PL to understand the problem

Hi Dr Mohammad Muhiuddin . The volume and shape of a nanoparticle determines how it interacts with light. Accordingly, this determines the color of a nanoparticle solution. See the RG link: Article Color My Nanoworld

See the following link: https://nanocomposix.com/pages/silver-nanoparticles-optical-properties

Also see the following RG link: Chapter Synthesis of Silver Nanoparticles

Kindly see also the following link: https://www.nanowerk.com/nanotechnology-news2/newsid=53439.php

I don't know whether you are trying for green nano systhesis ? - https://www.degruyter.com/document/doi/10.1515/gps-2016-0075/html