We prepared a Y 2 O 3 :Er,Yb nanoparticles by laser ablation in liquid. The laser used the second harmonic generation Nd:YAG (532 nm). A preparation process and measurement of upconversion properties were performed by varying the range of the energy density of the laser. Images from scanning electron microscopy (SEM) indicated that two types of nanoparticles existed in the product of laser ablation in liquid. We concluded the following: one type of nanoparticles was prepared from the nucleation of materials in a plume and the other was prepared by fragmentation. In the photoluminescence spectra, green (2 H 11/2 , 4 S 3/2 → 4 I 15/2) and red (4 F 7/2 → 4 I 15/2) fluorescence were observed using a 980 nm laser diode (LD) as the excitation source. We confirmed that the fluorescence intensity increased with increasing energy density of the laser. Thus, we concluded that the number of the nanoparticles increased as the energy density of the laser was increased.

2 ©2013.This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ Doi:10.1016/j.jlumin.2012.12.033Y2O3:Er,Yb nanoparticles were successfully prepared by laser ablation in liquid, and their upconversion properties were investigated. The particles were prepared by irradiating a Y2O3:Er,Yb target in water with a 532-nm pulsed laser beam. The prepared nanoparticles were determined to be composed of Y2O3, without any by-products, by X-ray diffraction. The average particle size of the nanoparticles measured by electron microscopy was a few tens of nanometers, which depended on the energy density of the irradiating laser beam. Upconversion luminescence of the nanoparticles was observed by the excitation of the laser diode at a wavelength of 980 nm. An increase by 33 % in the ratio of red emission ( 4 F9/2 → 4 I15/2) to green emission ( 2 H11/2/ 4 S3/2 → 4 I15/2) was observed with a decrease in the size of the nanoparticles from 21.5 nm to 11.1 nm. This high ratio is useful for biomedical applications because of the high transparency of this wavelength in the human body. The number of photons generated by the upconversion luminescence of the nanoparticles was investigated.The number of photons involved in the process of the nanoparticles was three, which was attributed to nonradiative relaxation due to the large specific surface area of the particles; in contrast, the normal number of photons involved in the process of Y2O3:Er,Yb bulk is two. ©2013.This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Y2O3:Er,Yb nanoparticles were prepared by laser ablation in water. We investigated crystallinity, distribution of dopant, and optical properties of the prepared nanoparticles. The full-width half-maximum (FWHD) of the crystalline peak of nanoparticles measured by an X-ray diffractometer (XRD) barely changed. Further, using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX), we confirmed the peaks of Y, Er, Yb, and O. Moreover, on the basis of the optical properties of the nanoparticles, the emission of red ( 2 F9/2 → 4 I15/2) and green ( 2 H11/2, 4 S3/2 → 4 I15/2) was confirmed. We also investigated the emission intensity as a function of the excitation power of 980 nm LD in the prepared nanoparticles. The photon avalanche effect was observed at the excitation power of 100 mW. These results confirmed that uniformly Er-Yb-doped Y2O3 nanoparticles were successfully prepared by laser ablation in water.

Y 2 O 3 :Er,Yb upconversion nanoparticles were prepared by laser ablation in liquid and capped with poly(ethylene glycol) (PEG). A Nd:YAG green laser with nanosecond pulse duration was used. Capping was carried out by a two-step process. The first step is surface modification using a silane coupling agent, (3-aminopropyl)triethoxysilane (APTES), to aminate the surface of nanoparticles. The second step was the conjugation of PEG chains to the surface by amido binding reaction between the surface amino groups and activated esters connected to PEG. The prepared upconversion nanoparticles were highly crystalline polycrystals, the particle size of which was approximately 20 nm. Dopants in phosphor nanoparticles were not removed by laser irradiation. The spectra of PEG-capped nanoparticles were almost the same as those of uncapped nanoparticles. The capped nanoparticles would be useful for biomedical applications.