title: Temperature-dependent upconversion luminescence and dynamics of NaYF4:Yb3+/Er3+ nanocrystals: influence of particle size and crystalline phase.
abstract: Oleic acid-capped NaYF4:Yb(3+)/Er(3+) upconversion nanocrystals (UCNCs) with different sizes and crystalline phases were prepared, and their temperature-dependent upconversion luminescence (UCL) and dynamics were studied. It is interesting to observe that the temperature-dependent behavior of UCL for the β-phase (25 nm, 45 nm and bulk) and α-phase (<10 nm) UCNCs is quite different. The UCL intensity of Er(3+) ions of the β-phase NaYF4 demonstrates a maximum around 100 K, while the intensity of the α-phase quenches monotonously with elevated temperature (10-400 K). The intensity ratio of (2)H11/2-(4)I15/2 to (4)S3/2-(4)I15/2, RHS, increases solely with temperature for β-phase NaYF4, while for the α-phase sample, it demonstrates a complex and indeterminate variation as a function of temperature. In the β-phase samples, rising processes were observed in the dynamics of Er(3+) ions, while in the α-phase sample, no rising process was observed and the decay processes of Er(3+) ions were bi-exponential. The rationale for these different temperature-dependent UCL properties was explained carefully.
authors.affiliation: State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun, 130012, People's Republic of China. songhw@jlu.edu.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Yu
authors.forename: Wen
authors.initials: W
authors.lastname: Xu
authors.forename: Hongwei
authors.initials: H
authors.lastname: Song
authors.forename: Shuang
authors.initials: S
authors.lastname: Zhang
mesh_terms: D004871:Erbium / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D049449:Luminescence; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D013696:Temperature; D015018:Ytterbium / Q000737:chemistry*; D015019:Yttrium / Q000737:chemistry*
chemical_list: C525362:sodium yttriumtetrafluoride; D015019:Yttrium; D004871:Erbium; D015018:Ytterbium; D005459:Fluorides