title: Size dependence of the upconverted luminescence of NaYF4:Er,Yb microspheres for use in ratiometric thermometry.
abstract: The size-dependent temperature sensitivity is observed on the upconversion luminescence of NaYF4:Er,Yb microspheres with sizes between 0.7 and 2 μm that are prepared by a poly(acrylic acid)-assisted hydrothermal process. It is found that the fluorescence intensity ratio (FIR) of their green upconversion emissions (with peaks at 521 and 539 nm) is strongly size-dependent at temperatures between 223 and 403 K. As the size of the spheres increases from 0.7 to 1.6 μm, the maximum sensitivity decreases from 36.8 × 10(-4) to 24.7 × 10(-4) K(-1). This effect is mainly attributed to the larger specific surface area of the smaller spheres where a relatively large number of Er(III) ions are located at the surface. This results in an increase in the efficiency of the (4)S3/2 → (2)H11/2 population process of the Er(III) ions due to stronger electron-phonon interactions with increasing T. Heating of the spheres by NIR light is also supposed to cause enhanced electron-phonon interactions in such particles.
authors.affiliation: Institute of Nano-Photonics, School of Physics and Materials Engineering, Dalian Nationalities University, Dalian, 116600, P. R. China. dong@dlnu.edu.cn.
authors.forename: Bin
authors.initials: B
authors.lastname: Dong
authors.forename: Rui N
authors.initials: RN
authors.lastname: Hua
authors.forename: Bao S
authors.initials: BS
authors.lastname: Cao
authors.forename: Zhi P
authors.initials: ZP
authors.lastname: Li
authors.forename: Yang Y
authors.initials: YY
authors.lastname: He
authors.forename: Zhen Y
authors.initials: ZY
authors.lastname: Zhang
authors.forename: Otto S
authors.initials: OS
authors.lastname: Wolfbeis
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D004583:Electrons; D004871:Erbium / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D008863:Microspheres; D010316:Particle Size; D017785:Photons; D013050:Spectrometry, Fluorescence; D015018:Ytterbium / Q000737:chemistry*; D015019:Yttrium / Q000737:chemistry*
chemical_list: D000180:Acrylic Resins; C525362:sodium yttriumtetrafluoride; C006903:carbopol 940; D015019:Yttrium; D004871:Erbium; D015018:Ytterbium; D005459:Fluorides