title: Investigation on the structure and upconversion fluorescence of Yb³⁺/Ho³⁺ co-doped fluorapatite crystals for potential biomedical applications.
abstract: Rare-earth Yb(3+) and Ho(3+) co-doped fluorapatite (FA:Yb(3+)/Ho(3+)) crystals were prepared by hydrothermal synthesis, and their structure, upconversion properties, cell proliferation and imaging were investigated. The synthesized crystals, with a size of 16 by 286 nm, have a hexagonal crystal structure of classic FA and a Ca/Yb/Ho molar ratio of 100/16/2.1. Several reasonable Yb(3+)/Ho(3+) -embedding lattice models along the fluorine channel of the FA crystal cell are proposed for the first time, such as models for (Ca7YbHo©)(PO4)6F2 and (Ca6YbHoNa2)(PO4)6F2. The activated FA:Yb(3+)/Ho(3+) crystals were found to exhibit distinct upconversion fluorescence. The 543- and 654-nm signals in the emission spectra could be assigned, respectively, to the (5)F4 ((5)S2) - (5)I8 and (5)F5 - (5)I8 transitions of holmium via 980-nm near-infrared excitation and the energy transfer of ytterbium. After the surfaces were grafted with hydrophilic dextran, the crystals displayed clear fluorescent cell imaging. Thus, the prepared novel FA:Yb(3+)/Ho(3+) upconversion fluorescent crystals have potential applications in the biomedical field.
authors.affiliation: Department of Biomedical Engineering, College of Engineering, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing, 100871, China.
authors.forename: Xiyu
authors.initials: X
authors.lastname: Li
authors.affiliation: Institute of Sports Medicine, Peking University Third Hospital, 49 North Garden Road, Haidian District, Beijing, 100191, China.
authors.forename: Jingxian
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Institute of Sports Medicine, Peking University Third Hospital, 49 North Garden Road, Haidian District, Beijing, 100191, China.
authors.forename: Zhentao
authors.initials: Z
authors.lastname: Man
authors.affiliation: Institute of Sports Medicine, Peking University Third Hospital, 49 North Garden Road, Haidian District, Beijing, 100191, China.
authors.forename: Yingfang
authors.initials: Y
authors.lastname: Ao
authors.affiliation: Department of Biomedical Engineering, College of Engineering, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing, 100871, China.
authors.forename: Haifeng
authors.initials: H
authors.lastname: Chen
mesh_terms: D001031:Apatites / Q000737:chemistry*; D058948:Cell Tracking / Q000379:methods*; D004735:Energy Transfer; D005453:Fluorescence; D005461:Fluorine / Q000737:chemistry; D006695:Holmium / Q000737:chemistry*; D015018:Ytterbium / Q000737:chemistry*
chemical_list: D001031:Apatites; D005461:Fluorine; C025105:fluorapatite; D015018:Ytterbium; D006695:Holmium