title: Sequential synthesis of type II colloidal CdTe/CdSe core-shell nanocrystals.
abstract: Colloidal type II CdTe/CdSe nanocrystals were synthesized by sequential addition of a tri-n-octylphosphine telluride (TOPTe)/TOP solution and several shell-precursor solutions to a CdO/TOP solution; the shell-precursor solutions consisted of CdO and TOPSe in TOP. For the growth of the CdTe core, the TOPTe/TOP solution was swiftly added to the CdO/TOP solution at a higher temperature (300 degrees C) than the growth temperature (250 degrees C). For the growth of the CdSe shell, in contrast, the CdO/TOPSe/TOP solution was slowly added to the CdTe/TOP solution at a lower temperature than the growth temperature (200-240 degrees C). The temporal evolution of the optical properties of the growing core-shell nanocrystals was monitored in detail. During the growth of the CdSe shell, the core-shell nanocrystals exhibited interesting changes in photoluminescence (PL) properties. The highest PL efficiency (approximately 38 %) was detected from core-shell nanocrystals with a CdSe shell thickness of 0.4-0.5 nm (indicated by TEM); the formation of the first monolayer is proposed. Our synthetic approach is well suited to a practical realization of engineering materials with bandgaps in the near-IR and IR spectral ranges.
authors.affiliation: Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada. kui.yu@nrc.ca
authors.forename: Kui
authors.initials: K
authors.lastname: Yu
authors.forename: Badruz
authors.initials: B
authors.lastname: Zaman
authors.forename: Svetlana
authors.initials: S
authors.lastname: Romanova
authors.forename: Da-shan
authors.initials: DS
authors.lastname: Wang
authors.forename: John A
authors.initials: JA
authors.lastname: Ripmeester
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry*; D003460:Crystallization; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles; D018036:Selenium Compounds / Q000737:chemistry*; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared; D013691:Tellurium / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D019187:Cadmium Compounds; D003102:Colloids; D018036:Selenium Compounds; C058667:cadmium selenide; D013691:Tellurium; C028337:cadmium telluride