Near-infrared frequency down-conversion and cross-relaxation in Eu~(2+)/Eu~(3+)-Yb~(3+) doped transparent oxyfluoride glass and glass-ceramics

摘要

In the present work, Eu~(2+)/Eu~(3+)-Yb~(3+) co-doped SiO_2-K_2O-BaF_2-La_2O_3-Sb_2O_3 oxyfluoride glasses were synthesized by conventional melt quenching method to elucidate the cooperative energy transfer (CET) based frequency down conversion from Yb~(3+) ions under UV excitation. The in situ formation of divalent europium (Eu~(2+)) along with Eu~(3+) during high temperature synthesis of these glasses under ambient atmosphere has been perceived and was explained through optical basicity model. Frequency down-conversion due to emission of two near infrared photons at around 1 urn from Yb～(3+) ions has been realized upon excitation of Eu~(2+) ions under 286 nm and further enhancement of this frequency down-conversion has been observed upon ceramization of these glasses. The precipitation of BaF_2 nano-crystals in glass-ceramics causes reduction of Eu~(3+) ions to Eu~(2+) ions resulting in an enhancement in the cooperative energy transfer from Eu~(2+) to Yb~(3+). The weak contribution of Eu~(3+) excitation towards Yb~(3+) emission has been attributed to the cross-relaxation process via ~5D_0→~7F_6 (Eu~(3+)):~2F_(5/2)→~2F_(7/2) (Yb~(3+)) route. The donor (Eu~(2+)/Eu~(3+))-acceptor (Yb~(3+)) concentration has been optimized at 0.5mol% Eu_2O_3 and 1.0 mol% Yb_2O_3 to achieve maximum down-conversion intensity near 1 μm.