title: Enhancing multiphoton upconversion through energy clustering at sublattice level.
abstract: The applications of lanthanide-doped upconversion nanocrystals in biological imaging, photonics, photovoltaics and therapeutics have fuelled a growing demand for rational control over the emission profiles of the nanocrystals. A common strategy for tuning upconversion luminescence is to control the doping concentration of lanthanide ions. However, the phenomenon of concentration quenching of the excited state at high doping levels poses a significant constraint. Thus, the lanthanide ions have to be stringently kept at relatively low concentrations to minimize luminescence quenching. Here we describe a new class of upconversion nanocrystals adopting an orthorhombic crystallographic structure in which the lanthanide ions are distributed in arrays of tetrad clusters. Importantly, this unique arrangement enables the preservation of excitation energy within the sublattice domain and effectively minimizes the migration of excitation energy to defects, even in stoichiometric compounds with a high Yb(3+) content (calculated as 98 mol%). This allows us to generate an unusual four-photon-promoted violet upconversion emission from Er(3+) with an intensity that is more than eight times higher than previously reported. Our results highlight that the approach to enhancing upconversion through energy clustering at the sublattice level may provide new opportunities for light-triggered biological reactions and photodynamic therapy.
authors.affiliation: 1] Department of Chemistry, National University of Singapore, Singapore 117543, Singapore [2].
authors.forename: Juan
authors.initials: J
authors.lastname: Wang
authors.affiliation: 1] Department of Chemistry, National University of Singapore, Singapore 117543, Singapore [2].
authors.forename: Renren
authors.initials: R
authors.lastname: Deng
authors.affiliation: Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada.
authors.forename: Mark A
authors.initials: MA
authors.lastname: MacDonald
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
authors.forename: Bolei
authors.initials: B
authors.lastname: Chen
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
authors.forename: Jikang
authors.initials: J
authors.lastname: Yuan
authors.affiliation: Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 117602, Singapore.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.affiliation: Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 117602, Singapore.
authors.forename: Dongzhi
authors.initials: D
authors.lastname: Chi
authors.affiliation: 1] Department of Chemistry, National University of Singapore, Singapore 117543, Singapore [2] Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 117602, Singapore.
authors.forename: Tzi Sum Andy
authors.initials: TS
authors.lastname: Hor
authors.affiliation: Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Argonne National Laboratory, Chemical Sciences and Engineering Division, Argonne, Illinois 60439, USA.
authors.forename: Guokui
authors.initials: G
authors.lastname: Liu
authors.affiliation: Advanced Membrane and Porous Materials Center, Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
authors.forename: Yu
authors.initials: Y
authors.lastname: Han
authors.affiliation: 1] Department of Chemistry, National University of Singapore, Singapore 117543, Singapore [2] Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 117602, Singapore.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Liu