Selective modification of the Er3+ 4I11/2 branching ratio by energy transfer to Eu3+

We present an investigation of Er^{3 +} photoluminescence in Y₂O₃ waveguides codoped with Eu^{3 +}. As a function of europium concentration we observe an increase in decay rate of the erbium ⁴I_11/2 energy level and an increase of the ratio of photoluminescence emission from the ⁴/_13/2 and ⁴/_11/2 states. Using a rate equation model, we show that this is due to an energy transfer from the ⁴/_11/2®⁴/_13/2 transition in erbium to europium. This increases the branching ratio of the ⁴/_11/2 state towards the ⁴/_13/2 state and results in a higher steady state population of the first excited state of erbium. Absolute intensity enhancement of the ⁴/_13/2 emission is obtained for europium concentrations between 0.1 and 0.3 at. %. In addition, the photoluminescence due to upconversion processes originating from the ⁴/_11/2 state is reduced. Using such state-selective energy transfer the efficiency of erbium doped waveguide amplifiers can be increased.