Cooperative energy transfer in silica fibres doped with ytterbium and terbium

Resonant excitation Yb3+ at 974 nm (10267 /cm) in codoped Yb3+-Tb3+ silica based fibres has lead to luminescence clearly being visible from the Tb3+ 5D4 level (20661 /cm). Through time resolved fluorescence measurements we have been able to directly assign the process responsible for the fluorescence to cooperative sensitisation of the Tb3+ 5D4 level by two excited Yb3+ ions. Energy transfer times for the cooperative process have been directly measured, enabling the effects of glass structure on the cooperative process to be explored. Numerical simulations based on the experimental findings have been conducted, enabling both the mechanism for the luminescence to be confirmed and the properties associated with the luminescence to be interpreted