title: Enhanced upconversion emission in colloidal (NaYF4:Er(3+))/NaYF4 core/shell nanoparticles excited at 1523 nm.
abstract: In this work, we report on efficient visible and near-IR upconversion emissions in colloidal hexagonal-phase core/shell NaYF4:Er(3+)/NaYF4 nanoparticles (∼38  nm) under IR laser excitation at 1523 nm. Varying amounts of Er(3+) dopants were introduced into the core NaYF4:Er(3+) nanoparticles, revealing an optimized Er(3+) concentration of 10% for the highest luminescent efficiency. An inert epitaxial shell layer of NaYF4 grown onto the core of the NaYF4:Er(3+) 10% nanoparticle increased its upconversion emission intensity fivefold due to suppression of surface-related quenching mechanisms, yielding the absolute upconversion efficiency to be as high as ∼3.9±0.3% under an excitation density of 18  W/cm(2). The dependence of the intensity of upconversion emission peaks on laser excitation density in the core/shell nanoparticle displayed "saturation effects" at low excitation density in the range of 1.5-18  W/cm(2), which again demonstrates high upconversion efficiency.
authors.forename: Wei
authors.initials: W
authors.lastname: Shao
authors.forename: Guanying
authors.initials: G
authors.lastname: Chen
authors.forename: Jossana
authors.initials: J
authors.lastname: Damasco
authors.forename: Xianliang
authors.initials: X
authors.lastname: Wang
authors.forename: Aliaksandr
authors.initials: A
authors.lastname: Kachynski
authors.forename: Tymish Y
authors.initials: TY
authors.lastname: Ohulchanskyy
authors.forename: Chunhui
authors.initials: C
authors.lastname: Yang
authors.forename: Hans
authors.initials: H
authors.lastname: Ågren
authors.forename: Paras N
authors.initials: PN
authors.lastname: Prasad
mesh_terms: D003102:Colloids / Q000737:chemistry / Q000528:radiation effects; D004735:Energy Transfer; D004871:Erbium / Q000737:chemistry* / Q000528:radiation effects; D005459:Fluorides / Q000737:chemistry* / Q000528:radiation effects*; D007259:Infrared Rays; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000528:radiation effects*; D015019:Yttrium / Q000737:chemistry* / Q000528:radiation effects*
chemical_list: D003102:Colloids; C525362:sodium yttriumtetrafluoride; D015019:Yttrium; D004871:Erbium; D005459:Fluorides