You can find from the following review provides a detailed analysis of the various factors affecting the morphology, size, and yield of metal nanoparticles.
Acta Naturae. 2014 Jan-Mar; 6(1): 35–44.
“Green” Nanotechnologies: Synthesis of Metal Nanoparticles Using Plants
As in this case variable is concentration and pH. Vary one when other is fixed and repeat for other. You may get various morphology. If sunlight is used it is fixed. If temperature is used the variable increases. In gamma chamber, pH was varied to get various morphology.