Down- And Upconversion Phenomena In Gd-3(Al,Ga)(5)O-12 Crystals Doped With Pr3+ And Yb3+ Ions

Single crystals of Gd3Al2.5Ga2.5O12, single doped with Pr3+ ions and double-doped with Pr3+ and Yb3+ ions, were fabricated by the Czochralski technique. Transition intensities and relaxation dynamics of Pr3+ ions were determined employing the Judd-Ofelt treatment. Crystal field splitting of excited multiplets of incorporated luminescent ions were determined on the basis of optical spectra recorded at liquid helium temperature. The Pr3+ -> Yb3+ energy-transfer phenomena were determined analyzing the effect of Yb3+ concentration on luminescence spectra and decay curves of 475 Pr3+ ions. It was concluded that the observed downconversion phenomenon involves a quantum-cutting mechanism consisting of a two-step energy transfer from Pr3+ to Yb3+. We observed a phenomenon of nonresonant conversion of femtosecond pulses of infrared light into visible Pr3+ emission that was weakly affected by the wavelength of incident light at least in the 1100-1600 nm region. It was concluded that excitation mechanisms consist of multiphoton absorption of incident infrared radiation involving interconfigurational 4f(2)-4f(1)5d transitions of Pr3+ and/or indirect excitation of Pr3+ ions by energy transfer from electrons created in the conduction band of the host.