Are you particles capped or are they naked? Using long chained ligands molecules (i.e. oleic acid) would allow you to redisperse your particle easily in solvents like alkanes or chloromethanes.

You know, in industry, there are always losses during manufacturing. Adherence to walls of containers as long as you are regaining at least 75% of your product should not be a concern. Otherwise you need to do a cost consideration when you want to increase your recovery efficiency meaning the time, labor, solvent, waste, etc must be considered before worrying about small losses due to product adherence to containers. On the otherhand, when more than 25% is lost due to adherence, you may want to change the container into one with lesser adsorpton capacity for your products. You can do this by testing centrifuge tubes made from various materials. The other thing you can do is to change your solvent to one that can increase the solubility of your NPs. Be careful that the NPs that adhered to the walls of the tube are no longer dispersible because this will not bring good mobility properties to your final product.

The CdS are PVP capped

As the washing steps consists in removing gradually the reaction medium, it's good to alternate mixture of solvent for dispersion (followed by vigorous stirring with vortex mixer) followed by adding a non-solvent (ratio solvent/nonsolvent > 3 to 5) and centrifuging. In your case, PVP makes the particles' surface polar (hydrophilic). Logically you can use DI water or alcohols (or a mixture of them) as solvent, and then a non-polar solvent (toluene? hexane? not sure). The best at that stage is to put small drop of dispersed QDs in different non-polar solvent available in your lab and look at which one looks to precipitate the fastest.

Good luck