title: Intense ultraviolet upconversion luminescence from hexagonal NaYF4:Yb3+/Tm3+ microcrystals.
abstract: Under 980 nm excitation, unusual 3P2-->3H6 (approximately 264 nm) and 3P2-->3F4 (approximately 309 nm) emissions from Tm3+ ions were observed in hexagonal NaYF4:Yb3+ (20%)/Tm3+ (1.5%) microcrystals. In comparison with the strong emissions from 1D2 and 1I6, the emissions from 1G4 and 3H4 almost vanished due to the efficient cross-relaxation of 1G4 + 3H4-->3F4 + 1D2(Tm3+). Double logarithmic plots of the upconversion emission intensity versus the excitation power are neither straight lines nor typical saturation curves. Theoretical analysis indicated that the complicated dependent relationships were mainly caused by phonon-assisted energy transfers and nonradiative relaxation.
authors.affiliation: State Key Laboratory on Integrated Optoelectronics, College of Electronic Science & Engineering, Jilin University, Changchun 130012, P. R. China.
authors.forename: Guofeng
authors.initials: G
authors.lastname: Wang
authors.forename: Weiping
authors.initials: W
authors.lastname: Qin
authors.forename: Lili
authors.initials: L
authors.lastname: Wang
authors.forename: Guodong
authors.initials: G
authors.lastname: Wei
authors.forename: Peifen
authors.initials: P
authors.lastname: Zhu
authors.forename: Ryongjin
authors.initials: R
authors.lastname: Kim
mesh_terms: D003198:Computer Simulation; D004735:Energy Transfer; D005459:Fluorides / Q000737:chemistry* / Q000528:radiation effects*; D008029:Lighting / Q000379:methods*; D008904:Miniaturization; D008956:Models, Chemical; D014466:Ultraviolet Rays; D015019:Yttrium / Q000737:chemistry* / Q000528:radiation effects*
chemical_list: C525362:sodium yttriumtetrafluoride; D015019:Yttrium; D005459:Fluorides