Er3+-catalyzed interdiffusion of elements across the interface between Bi2O3 film and SiO2 substrate resulting in host-material-specific photoluminescence spectra of Er3+

Abstract

Er3+-doped Bi2O3 thin films were sputter-deposited on SiO2 substrates under various process conditions. After post annealing in an O2 atmosphere, near-infrared photoluminescence (PL) spectra from Er3+ ions in specific product oxides were observed. For sufficiently oxidized Bi2O3:Er films with Er contents less than 1.5 at%, α-Bi2O3:Er having a monoclinic structure nucleated with negligible intermixing of the elements across the interface. Its PL spectra exhibited Er3+ luminescence signals consisting of eight Stark splitting peaks. Deposition at temperatures higher than 400 °C and/or with high Er content produced a somewhat reduced Bi2O3 network. Post annealing triggered diffusion of Si into the film as well as diffusion of Bi and Er into the SiO2 substrate, creating Bi2O3 −SiO2 −Er2O3 compound oxides. The original film body crystallized into a δ-Bi2O3 structure, which was stabilized by the presence of a large amount of Er. The emission-active product at Er contents of 2 at% was Bi2O3:Er−SiO2 (Bi2SiO5:Er), which exhibited four-line emission spectra and the intensity was lower than that of α-Bi2O3:Er. For Er3+ contents higher than 4 at%, interdiffusion of Si and O atoms was enhanced and SiOx:Er domains were created in the Bi2O3:Er film. Intense and broad emission peaks at 1530 and 1560 nm were observed in the PL spectra. The emission-active species in the Bi2O3 −SiO2 −Er2O3 compound oxide will be either Er3+ doped in the strongly disordered δ-Bi2O3 lattice involving oxygen deficiencies or Er3+ attached to SiOx domains formed inside the δ-Bi2O3 network.