Resonant energy transfer in praseodymium-thulium codoped ZBLAN fibre

The authors have designed a thulium and praseodymium codoped ZBLAN fluoride fibre to investigate energy transfer processes between Tm³⁺ (donor) and Pr³⁺ (acceptor) ions. The concentrations (3000 ppm Tm³⁺ and 500 ppm Pr³⁺) were selected to maximise the absorption of the Tm³⁺ and energy transfer while minimising self-quenching. To characterise the codoped system, they measured the visible fluorescence emissions and their radiative lifetimes at 540 nm in both preform and fibre materials and compared the values obtained with those expected from single dopants. The energy-transfer processes have been further investigated by comparison with a rate equation model. The transfer rate obtained from the measurements is 300 s^-1, and the predicted and observed fluorescence from the fibre are in good agreement.