Study of the optical properties and cross relaxation process of Dy3+ under simultaneous UV-IR excitation in tellurite glasses

The purpose of this paper is to present a new spectroscopic experimental technique to study the contributions of the different cross-relaxation mechanisms observed in Dy3+ doped TeO2-GeO2-ZnO glasses, based on the luminescence decay curves from F-4(9/2) -> H-6(13/2) (at 573 nm) transition of Dy3+ ions under spatial and temporal simultaneous UV (H-6(15/2) -> P-6(7/2)) and IR (H-6(15/2) -> F-6(3/2), H-6(15/2) -> H-6(7/2) and H-6(15/2) -> H-6(9/2)) excitations, for which the results are reported. The spectroscopic characterization was carried out through Raman, optical absorption, luminescence decay time profiles, and energy transfer as a function of Dy3+ ions content (0.5-5%). Emission spectra measurements indicated that concentration quenching is active in the samples. The lifetime decay of emission at 573 nm (F-4(9/2) level) was studied under excitation at 355 nm. At lower concentration of Dy3+, the temporal behavior of the emission at 573 nm is exponential, however, it becomes non-exponential as the concentration increases. The emission decay curves at 573 nm were fitted to Inokuti-Hirayama model and an energy transfer process dominated by an electric dipole-dipole interaction was deduced. A shortened lifetime was observed as the dysprosium ion content increased, which is attributed to non-radiative energy transfer between Dy3+ ions through the cross-relaxation mechanism. The analysis of the F-4(9/2) -> H-6(13/2) (573 nm) emission decays, obtained under simultaneous excitation at 355 nm and at different infrared excitations H-6(15/2) -> F-6(3/2) (905 nm), H-6(15/2) -> H-6(7/2) (1100 nm) and H-6(15/2) -> H-6(9/2) (1285 nm), allowed the determination of the dominant process in the cross-relaxation mechanism at high and low concentrations of Dy3+. It was possible to infer that in the glass with low concentration of Dy3+ the mechanism occurs predominantly by F-4(9/2) + H-6(15/2) -> F-6(11/2) + F-6(3/2) channel, and for high concentration of Dy3+, the channels F-4(9/2) + H-6(15/2) -> F-6(11/2) + F-6(3/2), F-9/2 + H-6(15/2) -> F-6(5/2) + F-6(9/2) + H-5(7/2), and F-4(9/2) + H-6(15/2) -> F-6(3/2) + F-6(11/2) + H-5(9/2) have a similar contribution to the Dy3+-Dy3+ resonant energy transfer.