title: A spectroscopic analysis of blue and ultraviolet upconverted emissions from Gd3Ga5O12:Tm3+, Yb3+ nanocrystals.
abstract: The spectroscopic behavior of gadolinium gallium garnet (Gd3Ga5O12, GGG) nanocrystals codoped with 1% each of Tm3+ and Yb3+ prepared via a solution combustion synthesis procedure was investigated. Initial excitation of the codoped nanocrystals with 465.8 nm (into the 1G4 state) showed a dominant blue-green emission ascribed to the 1G4-3H6 transition as well as red and NIR emissions from the 1G4-3F4 and 1G4-3H5/3H4-3H6 transitions, respectively. Excitation at this wavelength (465.8 nm) showed the existence of a Tm3+ --> Yb3+ energy transfer process evidenced by the presence of the 2F5/2-2F7/2 Yb3+ emission in the NIR emission spectrum. The decay time constants proved that the transfer of energy occurred via the 3H4 state. Following excitation of the Yb3+ ion with 980 nm, intense upconverted emission was observed. Emissions in the UV (1D2-3H6), blue (1D2-3F4), blue-green (1G4-3H6), red (1G4-3F4), and NIR (1G4-3H5/3H4-3H6) were observed and were the direct result of subsequent transfers of energy from the Yb3+ ion to the Tm3+ ion. Power dependence studies showed a deviation from expected values for the number of photons involved in the upconversion thus indicating a saturation of the upconversion process. An energy transfer efficiency of 0.576 was determined experimentally.
authors.affiliation: Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montreal, QC, H4B 1R6, Canada.
authors.forename: Fabiano
authors.initials: F
authors.lastname: Pandozzi
authors.forename: Fiorenzo
authors.initials: F
authors.lastname: Vetrone
authors.forename: John-Christopher
authors.initials: JC
authors.lastname: Boyer
authors.forename: Rafik
authors.initials: R
authors.lastname: Naccache
authors.forename: John A
authors.initials: JA
authors.lastname: Capobianco
authors.forename: Adolfo
authors.initials: A
authors.lastname: Speghini
authors.forename: Marco
authors.initials: M
authors.lastname: Bettinelli