Reduction of silver salts to Ag NPs is achieved much easier than reduction of copper(II) to copper NPs. Therefore, in the green method you have used perhaps reduction of copper has not occurred. However, the xrd of the product can tell you if you have obtained copper NPs.

Silver will appear pale or golden yellow with uv band about 400-450 nm.

Copper will appear brown and need good capping to show stability and uv peak at about 450-600 nm- anywhere?.

Check.

Otherwise

Grey silver powder and brown copper poder should be isolated via centrifugation and analyse them by xrd, match with reported data

My experience from PdNPs, colour change means Pd adsorption, but not necessarily means PdNPs. You'd better check NPs under TEM, or use XPS to check chemical state, or use XRD to check if there is crystal structure.

Cheers

what do you infer from this spectrum?

AgNPs will turn the color to brown

In my opinion, the change of the colour may indicate new chemical phase produced, but not sure if their sizes was at nano scale. Need to check under microscopy such as TEM.

Copper nanoparticles formation indicates the presence of brown to black precipitate which shows SPR at 450-650 nm under UV-Vis Spectra. U can also confirm its presence by taking XRD, SEM-EDX etc..

Thanks. I hope this information will help you..

Color change indicate change in oxidation state of metal but to ensure that nano particles are formed, one need to use appropriate surface protection. Ag , Au, Cu nano can be analyzed by uv-visible spectroscopy

Reducing the concentration of precursor (Copper) might help.