title: Synthesis of Cd-free water-soluble ZnSe(1-x)Te(x) nanocrystals with high luminescence in the blue region.
abstract: Cd-free core-shell nanocrystals (ZnSe(1-x)Te(x)/ZnS, 0<or=x<or=0.5) emitting in the pure blue region were prepared using an aqueous colloidal method followed by post-preparative ultraviolet irradiation. The photoluminescence (PL) efficiency and peak wavelength were maximized (40%, 448 nm) through a heat treatment of the nanocrystals during irradiation in a Zn(2+)-containing thiol solution. Because of the small lattice mismatch between ZnSe(1-x)Te(x) and ZnS, post-preparative irradiation at high temperature resulted in the formation of a thick ZnS shell (ca. 1.6 nm) around the core (ca. 2.2 nm in diameter) without deterioration of PL efficiency. Surface substitution of Te by S and size-selective precipitation of nanocrystals before ultraviolet irradiation resulted in intense PL. Quantum mechanical calculations show that the wave function of the electron of the exciton in the Te-containing core extends well into the ZnS shell. The calculations also reveal that a thick shell can confine the electrons inside the particles and thereby improve the PL efficiency and stability against the pH of the solution. Nanocrystals that had been post-preparatively irradiated showed good stability in solution and in a glass matrix even after months of storage in air.
authors.affiliation: Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan.
authors.forename: Chunliang
authors.initials: C
authors.lastname: Li
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nishikawa
authors.forename: Masanori
authors.initials: M
authors.lastname: Ando
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Enomoto
authors.forename: Norio
authors.initials: N
authors.lastname: Murase
mesh_terms: D011232:Chemical Precipitation; D003102:Colloids; D049449:Luminescence; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010316:Particle Size; D010777:Photochemistry; D045663:Quantum Dots; D018036:Selenium Compounds; D012995:Solubility; D013053:Spectrophotometry; D013499:Surface Properties; D013691:Tellurium; D014867:Water; D017967:Zinc Compounds
chemical_list: D003102:Colloids; D018036:Selenium Compounds; D017967:Zinc Compounds; D014867:Water; D013691:Tellurium; C044696:zinc selenide