title: Role of free cadmium and selenium ions in the potential mechanism for the enhancement of photoluminescence of CdSe quantum dots under ultraviolet irradiation.
abstract: The present study describes an enhancement of the photoluminescence of CdSe quantum dots under long-term ultraviolet irradiation in organic solvents. The photoenhancement effect followed multiexponential kinetics and was found to depend on several factors: intensity of ultraviolet light, polarity of the solvent, presence of capping agents on the nanocrystal surface, and presence of free Cd and Se ions in the solution. High intensity ultraviolet irradiation provoked a rapid enhancement of the photoluminescence of CdSe nanocrystals, reaching the maximum with subsequent photoluminescence decay. Low-intensity ultraviolet irradiation provoked a comparatively slow enhancement of the photoluminescence of CdSe nanocrystals, reaching saturation after 5-6 hours of irradiation in organic solvents (butanol and chloroform). The photoenhancement effect was reversible or irreversible depending on the additional ingredients. The role of free Cd and Se in these processes was clarified. The results are discussed in the context of ultraviolet induced liberation of free Cd and Se ions from the nanocrystal surface and their hypothetical reversible deposition with trapping of the surface holes and influencing the efficiency of radiative versus nonradiative exciton decay during the enhancement of photoluminescence.
authors.affiliation: Single-Molecule Bioanalysis Laboratory, National Institute for Advanced Industrial Science and Technology, AIST-Shikoku, 2217-14 Hayashi-Cho, Takamatsu, Kagawa 761-0395, Japan.
authors.forename: Rumiana
authors.initials: R
authors.lastname: Bakalova
authors.forename: Zhivko
authors.initials: Z
authors.lastname: Zhelev
authors.forename: Rajan
authors.initials: R
authors.lastname: Jose
authors.forename: Toshimi
authors.initials: T
authors.lastname: Nagase
authors.forename: Hideki
authors.initials: H
authors.lastname: Ohba
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Baba
mesh_terms: D002104:Cadmium / Q000737:chemistry / Q000528:radiation effects; D019187:Cadmium Compounds / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects*; D007477:Ions; D008163:Luminescent Measurements / Q000295:instrumentation / Q000379:methods*; D008422:Materials Testing; D008956:Models, Chemical; D010777:Photochemistry / Q000379:methods*; D045663:Quantum Dots; D012643:Selenium / Q000737:chemistry / Q000528:radiation effects; D018036:Selenium Compounds / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D019187:Cadmium Compounds; D007477:Ions; D018036:Selenium Compounds; D002104:Cadmium; C058667:cadmium selenide; D012643:Selenium