title: Investigation of the emission mechanism in milled SrAl₂O₄:Eu, Dy using optical and synchrotron X-ray spectroscopy.
abstract: There currently exists much debate as to the active state related to the "long afterglow" effect in europium doped oxide materials. Redox couples that consist of Eu(+/2+) and Eu(2+/3+) are discussed, but no common answer is currently accepted. Here, we present a comparison of the optical properties of a commercially available SrAl(2)O(4):Eu, Dy phosphor, as a function of nanoparticle size reduction via dry mechanical milling. X-ray and optical spectroscopic data indicate a significant decrease in phosphorescence efficiency and an increase in laser stimulated emission efficiency as near surface Eu(2+) ions are oxidized to Eu(3+) as a consequence of increased exposure during the milling process. These results show evidence only for Eu(2+/3+) oxidation states, suggesting the mechanism related to long afterglow effect does not arise from Eu(+) species. We also suggest that size reduction, as a rule, cannot be universally applied to improve optical properties of nanostructures.
authors.affiliation: Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469, United States.
authors.forename: Sanjeev Kumar
authors.initials: SK
authors.lastname: Kandpal
authors.forename: Ben
authors.initials: B
authors.lastname: Goundie
authors.forename: Joshua
authors.initials: J
authors.lastname: Wright
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Pollock
authors.forename: Michael D
authors.initials: MD
authors.lastname: Mason
authors.forename: Robert W
authors.initials: RW
authors.lastname: Meulenberg
mesh_terms: D005063:Europium / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D017356:Synchrotrons; D056928:X-Ray Absorption Spectroscopy
chemical_list: D010087:Oxides; D005063:Europium