title: Confining energy migration in upconversion nanoparticles towards deep ultraviolet lasing.
abstract: Manipulating particle size is a powerful means of creating unprecedented optical properties in metals and semiconductors. Here we report an insulator system composed of NaYbF4:Tm in which size effect can be harnessed to enhance multiphoton upconversion. Our mechanistic investigations suggest that the phenomenon stems from spatial confinement of energy migration in nanosized structures. We show that confining energy migration constitutes a general and versatile strategy to manipulating multiphoton upconversion, demonstrating an efficient five-photon upconversion emission of Tm(3+) in a stoichiometric Yb lattice without suffering from concentration quenching. The high emission intensity is unambiguously substantiated by realizing room-temperature lasing emission at around 311 nm after 980-nm pumping, recording an optical gain two orders of magnitude larger than that of a conventional Yb/Tm-based system operating at 650 nm. Our findings thus highlight the viability of realizing diode-pumped lasing in deep ultraviolet regime for various practical applications.
authors.affiliation: Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China.
authors.forename: Xian
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong SAR, China.
authors.forename: Limin
authors.initials: L
authors.lastname: Jin
authors.affiliation: Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Kong
authors.affiliation: Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China.
authors.forename: Tianying
authors.initials: T
authors.lastname: Sun
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong SAR, China.
authors.forename: Wenfei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China.
authors.forename: Xinhong
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China.|City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Fan
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong SAR, China.
authors.forename: Siu Fung
authors.initials: SF
authors.lastname: Yu
authors.affiliation: Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China.|City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China.
authors.forename: Feng
authors.identifier: http://orcid.org/0000-0001-9471-4386
authors.initials: F
authors.lastname: Wang