title: Magneto-Photoluminescence Based on Two-Photon Excitation in Lanthanide-Doped Up-Conversion Crystal Particles.
abstract: Experimental studies on magneto-photoluminescence based on two-photon excitation in up-conversion Y2O2S:Er, Yb crystal particles are reported. It is found that the up-conversion photoluminescence generated by two-photon excitation exhibits magnetic field effects at room temperature, leading to a two-photon excitation-induced magneto-photoluminescence, when the two-photon excitation exceeds the critical intensity. By considering the spin selection rule in electronic transitions, it is proposed that spin-antiparallel and spin-parallel transition dipoles with spin mixing are accountable for the observed magneto-photoluminescence. Specifically, the two-photon excitation generates spin-antiparallel electric dipoles between4S3/2-4I15/2in Er3+ions. The antiparallel spins are conserved by exchange interaction within dipoles. When the photoexcitation exceeds the critical intensity, the Coulomb screening can decrease the exchange interaction. Consequently, the spin-orbital coupling can partially convert the antiparallel dipoles into parallel dipoles, generating a spin mixing. Eventually, the populations between antiparallel and parallel dipoles reach an equilibrium established by the competition between exchange interaction and spin-orbital coupling. Applying a magnetic field can break the equilibrium by disturbing spin mixing through introducing spin precessions, changing the spin populations on antiparallel and parallel dipoles and leading to the magneto-photoluminescence. Therefore, spin-dependent transition dipoles present a convenient mechanism to realize magneto-photoluminescence in multiphoton up-conversion crystal particles.
authors.affiliation: Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Hengxing
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Qin
authors.affiliation: Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Mingxing
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Ting
authors.initials: T
authors.lastname: Wu
authors.affiliation: Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Hu
keywords: crystal fields; lanthanide-doped crystal particles; magneto-photoluminescence; two-photon absorption