title: Investigation of the internal heterostructure of highly luminescent quantum dot-quantum well nanocrystals.
abstract: In this paper, we report on the growth and characterization of quantum dot-quantum well nanostructures with photoluminescence (PL) that is tunable over the visible range. The material exhibits a PL efficiency as high as approximately 60% and is prepared by reacting ZnS nanocrystals in turn with precursors for CdSe and ZnS in an attempt to form a simple "ZnS/CdSe/ZnS quantum-well structure". Through the use of synchrotron radiation-based photoelectron spectroscopy in conjunction with detailed overall compositional analysis and correlation with the size of the final composite nanostructure, the internal structure of the composite nanocrystals is shown to consist of a graded alloy core whose composition gradually changes from ZnS at the very center to CdSe at the onset of a CdSe layer. The outer shell is ZnS with a sharp interface, probably reflecting the relative thermodynamic stabilities of the parent binary phases. These contrasting aspects of the internal structure are discussed in terms of the various reactivities and are shown to be crucial for understanding the optical properties of such complex heterostructured nanomaterials.
authors.affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Pralay K
authors.initials: PK
authors.lastname: Santra
authors.forename: Ranjani
authors.initials: R
authors.lastname: Viswanatha
authors.forename: Steve M
authors.initials: SM
authors.lastname: Daniels
authors.forename: Nigel L
authors.initials: NL
authors.lastname: Pickett
authors.forename: Jason M
authors.initials: JM
authors.lastname: Smith
authors.forename: Paul
authors.initials: P
authors.lastname: O'Brien
authors.forename: D D
authors.initials: DD
authors.lastname: Sarma
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D008163:Luminescent Measurements / Q000379:methods*; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013440:Sulfides / Q000737:chemistry*; D014961:X-Ray Diffraction; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; D013440:Sulfides; D017967:Zinc Compounds; C058667:cadmium selenide; C031238:zinc sulfide