A semiconductor nanocrystal can have a photoluminescent quantum yield of at least 90%, at least 95%, or at least 98%. The nanocrystal can be made by sequentially contacting a nanocrystal core with an M-containing compound and an X donor, where at least one of the M-containing compound and the X donor is substoichiometric with respect to forming a monolayer on the nanocrystal core.