title: Triplet-triplet annihilation upconversion in CdS-decorated SiO2 nanocapsules for sub-bandgap photocatalysis.
abstract: This study reports the first successful nanoscale encapsulation of triplet-triplet annihilation upconversion (TTA-UC) medium within a rigid silica shell using a self-assembly microemulsion process. These newly synthesized nanocapsules present a few critical advances that could be instrumental for a wide range of aqueous-based photonics applications, including photocatalysis, artificial photosynthesis, and bioimaging. The nanocapsules form a homogeneous suspension that can produce intense, diffuse UC emission in water without deoxygenation, closely resembling conventional TTA-UC processes that have been performed in deoxygenated organic solvents. The silica shell provides sites for further surface modification, which allows, when combined with its nanoscale dimension and structural rigidity, this TTA-UC system to acquire various useful functionalities. A benchmark TTA-UC pair, palladium(II) tetraphenyltetrabenzoporphyrin as a sensitizer and perylene as an acceptor, was used to demonstrate efficient red-to-blue (635 nm, 1.95 eV → 470 nm, 2.6 eV) upconversion in the oxygen-rich aqueous phase. The nanocapsule surface was further functionalized with cadmium sulfide nanoparticles (Eg = 2.4 eV) to demonstrate sub-bandgap sensitization and subsequent aqueous-phase catalytic oxidation.
authors.affiliation: Department of Chemical and Environmental, Engineering School of Engineering and Applied Science, Yale University , New Haven, Connecticut 06511, United States.
authors.forename: Oh Seok
authors.initials: OS
authors.lastname: Kwon
authors.forename: Jae-Hyuk
authors.initials: JH
authors.lastname: Kim
authors.forename: Jin Ku
authors.initials: JK
authors.lastname: Cho
authors.forename: Jae-Hong
authors.initials: JH
authors.lastname: Kim
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D002384:Catalysis / Q000528:radiation effects; D053769:Nanocapsules / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D010782:Photolysis; D012822:Silicon Dioxide / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D053769:Nanocapsules; D013440:Sulfides; C034939:cadmium sulfide; D012822:Silicon Dioxide; D010100:Oxygen
keywords: chromophores; inorganic nanocapsules; photocatalysis; triplet−triplet annihilation; upconversion