I went through one paper where it is mentioned that before stirring they have done ultrasonication for 2 hr at 50 degree C in co-precipitation process. And it was meant to make Cu-doped ZnO.
Generally precursors in the form of chlorides will dissolve easily in solvents. thus stirring itself reduces the size of the precursors to atomic scale. If you have not achieved any proper solubility in solvents. then you can go for ultrasonication process.