title: Synthesis of uniform disk-shaped copper telluride nanocrystals and cation exchange to cadmium telluride quantum disks with stable red emission.
abstract: We present the synthesis of novel disk-shaped hexagonal Cu2Te nanocrystals with a well-defined stoichiometric composition and tunable diameter and thickness. Subsequent cation exchange of Cu to Cd at high temperature (180 °C) results in highly fluorescent CdTe nanocrystals, with less than 1 mol % of residual Cu remaining in the lattice. The procedure preserves the overall disk shape, but is accompanied by a substantial reconstruction of the anion sublattice, resulting in a reorientation of the c-axis from the surface normal in Cu2Te into the disk plane in CdTe nanodisks. The synthesized CdTe nanodisks show a continuously tunable photoluminescence (PL) peak position, scaling with the thickness of the disks. The PL lifetime further confirms that the CdTe PL arises from band-edge exciton recombination; that is, no Cu-related emission is observed. On average, the recombination rate is about 25-45% faster with respect to their spherical quantum dots counterparts, opening up the possibility to enhance the emission rate at a given wavelength by controlling the nanocrystal shape. Finally, with a PL quantum efficiency of up to 36% and an enhanced PL stability under ambient conditions due to a monolayer of CdS formed on the nanocrystal surface during cation exchange, these flat quantum disks form an interesting enrichment to the current family of highly fluorescent, shape-controlled nanocrystals.
authors.affiliation: Istituto Italiano di Tecnologia, via Morego 30, IT-16163 Genova, Italy.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Li
authors.forename: Rosaria
authors.initials: R
authors.lastname: Brescia
authors.forename: Mauro
authors.initials: M
authors.lastname: Povia
authors.forename: Mirko
authors.initials: M
authors.lastname: Prato
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bertoni
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna
authors.forename: Iwan
authors.initials: I
authors.lastname: Moreels