Non-stabilized europium-doped lanthanum oxyfluoride and fluoride nanoparticles well dispersed in thin silica films

Abstract

Well dispersed non-stabilized lanthanum oxyfluoride and fluoride nanoparticles were prepared in situ in thin silica films from rapid thermal decomposition of lanthanum tris-trifluoroacetate under nitrogen atmosphere. The thin silica films were obtained from sol–gel method and spin-coating. The spectroscopic properties of the non-stabilized nanoparticles as well the nanoparticles dispersed into thin silica films were studied in order to apply the system in future photonic applications such as erbium(III)-doped waveguide amplifiers. The non-stabilized nanoparticles were characterized by XRD, FT-IR, Transmission Electron Microscopy, Confocal Raman Spectroscopy and steady-state and time-resolved Luminescence Spectroscopy and these characterizations were used as a starting point to characterize the nanoparticles dispersed into the films. According to the temperature of the thermal treatments, the non-stabilized nanoparticles may present Eu(III)-doped LaOF in tetragonal and rhombohedral phases as well as a mixed phase of Eu(III)-doped LaF₃ and LaOF. The tetragonal LaOF phase has C_4v La(III) point symmetry and is more symmetric than the rhombohedral LaOF phase, where the La(III) ion has C_3v symmetry, consequently tetragonal LaOF presented lower Ω₂ values than rhombohedral LaOF. Theoretical calculations of Judd–Ofelt intensity parameters were also performed and were in good agreement with the experimental values. The samples containing the mixed phase of LaF₃ and LaOF presented lower values of intensity parameters than pure LaOF phases. The samples containing the mixed phase presented higher values of emission lifetimes and quantum efficiencies. Confocal Raman spectroscopy of these samples complements the luminescence studies and indicates which LaOF phase is present in the mixed phase of LaF₃ and LaOF. The rapid thermal decomposition of the precursor tris-trifluoroacetate on thin silica films results in well-dispersed 10 nm nanoparticles. The mixed phase of LaF₃ and LaOF phases is also present in thin films. The luminescence of the Eu(III) and Er(III)/Yb(III)-doped LaF₃/LaOF nanoparticles containing thin silica films presented broad emission bands suggesting that in the future the systems may be applied as erbium(III)-doped waveguide amplifiers.