A method for preparing a core-shell nanocrystal can include mixing an M-containing precursor solution, an X-containing precursor solution, and an acid or alcohol in an inert atmosphere at a first temperature to form a reaction mixture; maintaining the reaction mixture at the first temperature to grow the MX core of the nanocrystal; raising the temperature of the reaction mixture to a second temperature; and maintaining the reaction mixture at the second temperature to grow a shell of the nanocrystal.