title: Copper-doped inverted core/shell nanocrystals with "permanent" optically active holes.
abstract: We have developed a new class of colloidal nanocrystals composed of Cu-doped ZnSe cores overcoated with CdSe shells. Via spectroscopic and magneto-optical studies, we conclusively demonstrate that Cu impurities represent paramagnetic +2 species and serve as a source of permanent optically active holes. This implies that the Fermi level is located below the Cu(2+)/Cu(1+) state, that is, in the lower half of the forbidden gap, which is a signature of a p-doped material. It further suggests that the activation of optical emission due to the Cu level requires injection of only an electron without a need for a valence-band hole. This peculiar electron-only emission mechanism is confirmed by experiments in which the titration of the nanocrystals with hole-withdrawing molecules leads to enhancement of Cu-related photoluminescence while simultaneously suppressing the intrinsic, band-edge exciton emission. In addition to containing permanent optically active holes, these newly developed materials show unprecedented emission tunability from near-infrared (1.2 eV) to the blue (3.1 eV) and reduced losses from reabsorption due to a large Stokes shift (up to 0.7 eV). These properties make them very attractive for applications in light-emission and lasing technologies and especially for the realization of novel device concepts such as "zero-threshold" optical gain.
authors.affiliation: Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Ranjani
authors.initials: R
authors.lastname: Viswanatha
authors.forename: Sergio
authors.initials: S
authors.lastname: Brovelli
authors.forename: Anshu
authors.initials: A
authors.lastname: Pandey
authors.forename: Scott A
authors.initials: SA
authors.lastname: Crooker
authors.forename: Victor I
authors.initials: VI
authors.lastname: Klimov
mesh_terms: D003300:Copper / Q000737:chemistry*; D008027:Light; D008163:Luminescent Measurements / Q000379:methods*; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D016062:Porosity; D012031:Refractometry / Q000379:methods*
chemical_list: D003300:Copper