title: Spectroscopic study of a UV-photostable organic-inorganic hybrids incorporating an Eu3+ beta-diketonate complex.
abstract: New europium and gadolinium tris-beta-diketonate complexes have been prepared and incorporated in sol-gel-derived organic-inorganic hybrids, named di-ureasils. The general formula [Ln(btfa)3(4,4'-bpy)(EtOH)] (Ln=Eu, Gd; 4,4'-bpy=4,4'-bipyridine; btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione) for the complexes was confirmed by X-ray crystallography and elemental analysis. The ground-state geometry of the Eu3+ complex was calculated from the Sparkle/AM1 model. The calculated quantum yield obtained from the Sparkle model and from the crystal structure (both 46%) are in satisfactory agreement with the experimental value (38+/-4%). In the isolated complex the most efficient luminescence channel is S0-->S1-->T-->(5D1, 5D0)-->7F0-6, where the exchange mechanism dominates in the energy-transfer channel T-->(5D1, 5D0). For the Eu3+-based di-ureasils a 50% quantum yield enhancement compared to the Eu3+ complex is observed, which suggests an effective hybrid host-metal ion interaction and an active energy-transfer channel between the hybrid host and the Eu3+ complex. The Eu3+-based di-ureasils are photostable under UVA (360 nm) excitation, whereas under UVB (320 nm) and UVC (290 nm) photodegradation occurs.
authors.affiliation: Departamento de Física, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Patricia P
authors.initials: PP
authors.lastname: Lima
authors.forename: Rute A
authors.initials: RA
authors.lastname: Sá Ferreira
authors.forename: Ricardo O
authors.initials: RO
authors.lastname: Freire
authors.forename: Filipe A
authors.initials: FA
authors.lastname: Almeida Paz
authors.forename: Lianshe
authors.initials: L
authors.lastname: Fu
authors.forename: Severino
authors.initials: S
authors.lastname: Alves
authors.forename: Luis D
authors.initials: LD
authors.lastname: Carlos
authors.forename: Oscar L
authors.initials: OL
authors.lastname: Malta