Upconversion fluorescence in Nd~(3+)/Yb~(3+) co-doped titanate glasses prepared by containerless method

摘要

Nd~(3+)/Yb~(3+) co-doped TiO_2-La_2O_3 glasses modified by ZrO_2 were fabricated by containerless method. Under the excitation of 980 nm lasers, three intense emissions centered at 521, 545, and 655 nm were observed, which are assigned to the Nd~(3+): ~4G_(9/2) → ~4I_(9/2), ~4G_(7/2) →~4I_(9/2), and ~4G_(7/2)→~4I_(13/2) transitions, respectively. Besides, two very weak emission bands at 496 and 603 nm were also found due to the Nd~(3+) transition of ~2G_(9/2) →~4I_(9/2) and ~4G_(5/2) (or ~2G_(7/2))→~4I_(9/2), respectively. Pumping powder dependence of emission intensity suggests a two-photon adsorption process responsible for the upconversion luminescence. A combined phonon-assisted and cooperative sensitization mechanism is presented to interpret the energy transfer from Yb~(3+) to Nd~(3+) ions. In addition, the highest intensity of luminescence was found for the glass with 1.2 mol% Nd~(3+), and the upconversion efficiency can be enhanced by increasing of ZrO_2 content.