Influence of Bi on the Er luminescence in yttrium- erbium disilicate thin films

The influence of bismuth on erbium optical properties at 1.54 mu m has been investigated in yttrium-erbium disilicate thin films synthesized by magnetron co-sputtering and implanted with two Bi different doses. The Bi depth distribution and the evolution of its oxidation states after annealing treatments at 1000 degrees C in two atmospheres, O-2 and N-2, have been investigated. It was found that only in O-2 the Bi3+ valence state is prevalent, thanks to the enhanced Bi mobility in the oxidizing ambient, as demonstrated by Rutherford backscattering spectrometry. At lower Bi content, although the formation of Bi 0 metallic nanoparticles that are deleterious non radiative channels for Er luminescence, efficient energy transfer from Bi to Er has been obtained only in O-2. It is due to the excitation of ultraviolet broad Bi3+ absorption band and the energy transfer to Er ions. We have evaluated that in this case, Er effective excitation cross section increased by a factor of 5 in respect with the one for direct Er absorption at 488 nm. At higher Bi dose, this mechanism is absent, but an increased Er optical efficiency at 1.54 mu m has been observed under resonant excitation. It is due to the contribution of a fraction of Er ions having an increased lifetime. This phenomenon is associated with the formation of Bi agglomerates, induced at higher Bi doses, which well isolate Er from non-radiative quenching centers. The increased decay time assures higher optical efficiency at 1.54 mu m. (C) 2014 AIP Publishing LLC.