Synthesis of quantum dots

A method, comprising:

• dissolving selenium and a cation precursor in a mixture of an aliphatic thiol and an aliphatic amine to form a first solution, the aliphatic thiol and aliphatic amine each independently having from 1 to 20 carbon atoms;
• heating the first solution to a first temperature of from 140° C. to 230° C. in 15 minutes or less;
• maintaining the first solution with a second temperature of from 210° C. to 240° C. for from 1 minute to 60 minutes to form quantum dot cores of a selected size;
• dissolving a shell precursor in a second mixture of the aliphatic thiol and the aliphatic amine to form a second solution;
• combining the second solution and the quantum dot cores to form a mixture;
• and
• heating the mixture to a third temperature of from 50° C. to 240° C.

A composition having a formula

• MSeyS1-y
• wherein M is zinc, and y is from greater than 0 to less than 1, the composition comprising quantum dots having a standard deviation in size distribution of less than 10%, and wherein the quantum dots are made by a method comprising
• preparing a phosphine-free solution at a temperature suitable to form the solution, the solution comprising
• a first precursor comprising zinc;
• a second precursor comprising selenium;
• a thiol;
• and
• an amine;
• and
• making the quantum dots by heating the solution to a temperature suitable to decompose the thiol and incorporate sulfur into the quantum dots for an amount of time of from greater than 0 minutes to 50 minutes.

A composition, comprising:

• quantum dots having a standard deviation in size distribution of less than 10%;
• and
• a core composition according to a formula
• MSexS2-x
• wherein
• M is a group IB metal, group IIIB metal, or a combination thereof;
• and
• x is from greater than 0 to less than 2.