*3.3. Preparation of Quantum Dots*

The synthesis of the Mn2+:ZnS Qds sample was done in our lab by the chemical precipitation method following the procedure reported earlier [5,59,71]. In brief, all the aqueous solutions of precursors were prepared first, i.e., manganese carbonate, sodium sulfide and zinc acetate. For 1% manganese doping, we added 29.75 mL of 0.01 mol/L of manganese carbonate solution to 49.5 mL of a solution of 0.5 mol/L zinc acetate. Then, nicotinic acid (1.0 At. wt%) was mixed for the capping action. The pH was adjusted to 10 using a solution of NaOH 1 M. Then a Na2S solution was added, dropwise, with continuous stirring to obtain a white precipitate. The solution was then refluxed at 60 ◦C

and centrifuged to obtain the precipitate. Finally, the precipitate was filtered, washed 3–4 times to eliminate impurities and dried.
