title: The two-photon excitation of SiO(2)-coated Y(2)O(3):Eu(3+) nanoparticles by a near-infrared femtosecond laser.
abstract: In order to improve the photoluminescence property of Eu(3+)-doped nanoparticles, Y(2)O(3):Eu(3+) nanoparticles were synthesized using the Pechini-type sol-gel method, then coated with SiO(2) shells by using the Stöber method for different coating times. The SiO(2)-coated nanoparticles were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, and their photoluminescence spectra were recorded under 800 nm femtosecond laser excitation. The results indicate that a two-photon simultaneous absorption upconversion luminescence is obtained, and their upconversion luminescence intensities are further enhanced after the surfaces of the nanoparticles are coated with different thickness SiO(2) shells. Compared to the upconversion luminescence intensity of non-coated nanoparticles at 611 nm, the upconversion luminescence intensities of SiO(2)-coated Y(2)O(3):Eu(3+) nanoparticles with coating times of 60, 90 and 120 min were enhanced by 3.30, 3.96 and 4.13 times, respectively. This can be attributed to the contributions of the increased amounts of Eu(3+) ions populated at the (5)D(0) level on the surfaces of the nanoparticles because the cooperative ligand fields between the Y(2)O(3) core and non-crystalline SiO(2) shell interfaces activate the 'dormant' Eu(3+) ions near or on the surfaces of the nanoparticles. From a Judd-Ofelt (J-O) theory analysis, the coated shell structures can improve the radiative quantum efficiencies of Eu(3+)-doped nanoparticles. It is therefore concluded that more intense red upconversion luminescence with high radiative quantum efficiencies can enable the SiO(2)-coated Y(2)O(3):Eu(3+) nanoparticles to have the great potential to be used as a fine resolution phosphor.
authors.affiliation: Department of Material Physics and Chemistry, School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, People's Republic of China. Center of Electron Microscope Technology, Mudanjiang Medical College, Mudanjiang 157011, People's Republic of China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Lü
authors.forename: Aihua
authors.initials: A
authors.lastname: Li
authors.forename: Fengyun
authors.initials: F
authors.lastname: Guo
authors.forename: Liang
authors.initials: L
authors.lastname: Sun
authors.forename: Liancheng
authors.initials: L
authors.lastname: Zhao