Selective modification of the Er3+ 4I11/2 branching ratio by energy transfer to Eu3+
We present an investigation of Er3 + photoluminescence in Y2O3 waveguides codoped with Eu3 +. As a function of europium concentration we observe an increase in decay rate of the erbium 4I11/2 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.
