Size dependence of the upconverted luminescence of NaYF4:Er,Yb microspheres for use in ratiometric thermometry

The size-dependent temperature sensitivity is observed on the upconversion luminescence of NaYF 4 :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 upconv...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2014-08, Vol.16 (37), p.29-212
Main Authors: Dong, Bin, Hua, Rui N, Cao, Bao S, Li, Zhi P, He, Yang Y, Zhang, Zhen Y, Wolfbeis, Otto S
Format: Article
Language:English
Subjects:
Acrylic Resins - chemistry
Electrons
Erbium - chemistry
Fluorides - chemistry
Microspheres
Particle Size
Photons
Spectrometry, Fluorescence
Ytterbium - chemistry
Yttrium - chemistry
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Summary:The size-dependent temperature sensitivity is observed on the upconversion luminescence of NaYF 4 :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 S 3/2 → 2 H 11/2 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. NaYF 4 :Er,Yb microspheres are reported as promising candidates for probes to sense the temperature on the micro/nano-scale but may also contribute to better interpretation of some of the results obtained in the past with UCNPs of varying sizes.
ISSN:1463-9076
1463-9084
DOI:10.1039/c4cp01966k