Rafael D. L. Gaspar

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

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 C4v La(III) point symmetry and is more symmetric than the rhombohedral LaOF phase, where the La(III) ion has C3v 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.

Luminescent properties of passivated europium(III)-doped rare earth oxide sub-10 nm nanoparticles

Passivated nanoparticles of europium(III)-doped yttrium, lanthanum and gadolinium oxides were synthesized by a modified sol–gel method and their luminescent properties were studied. The passivation of the nanoparticles surface is confirmed by infrared spectroscopy. Gadolinium and yttrium oxides crystalize as cubic phases while the lanthanum oxide has hexagonal phase. The emission spectra of the samples show broad transitions attributed to europium(III) ions probably due to structure disorder caused by the size and also by the high surface/volume ratio of the nanoparticles. The Judd–Ofelt intensity parameters were obtained from the emission spectra. The passivation of the nanoparticles surface, with trioctylphosphine oxide, does not significantly alter the values of Ω2 and Ω4 parameters and slightly increases the emission quantum efficiency of the nanoparticles that possesses lower values of Ω2 parameter than bulk samples.

Polydimethylsiloxane composites containing core-only lanthanide-doped oleylamine-stabilized LaF3 nanoparticles with high emission lifetimes

This work reports on the synthesis and spectroscopic characterization of oleylamine-stabilized lanthanide-doped LaF3 nanoparticles isolated or dispersed in polydimethylsiloxane (pdms). The hexagonal Eu(III)-doped LaF3 nanoparticles have the mean size of 6 nm and are stabilized by oleylamine molecules, allowing their dispersion in pdms. Surface effects modify the emission properties of the Eu(III)-doped LaF3 isolated nanoparticles implying different emission profiles. Isolated nanoparticles show higher Judd–Ofelt emission intensity parameter values than the bulk ones. Time-resolved luminescence spectroscopy and lifetime measurements indicate the presence of at least two different chemical environments for Eu(III) ions, one being at the nanoparticle surface and the other at the bulk. The upconversion emission mechanism of Er(III)/Yb(III) co-doped LaF3 nanoparticles is dependent on the relative amount of Er(III)/Yb(III) in the sample and it may be explained by 2.5 photons, instead of the traditional mechanism involving 2 photons. Oleylamine surface passivation of Eu(III)-doped LaF3 nanoparticles dispersed in pdms avoids the influence of the siloxane polymer on the luminescence properties, keeping their emission spectral profile unchanged. Er(III)/Yb(III) co-doped LaF3 nanoparticles exhibit the Er(III) 1540 nm emission with FWHM = 75 nm for isolated or pdms-dispersed nanoparticles, which may allow the application of such materials in polymer based erbium-doped planar waveguides. The modified methodology of synthesis allows obtaining lanthanide-doped LaF3 nanoparticles with high emission lifetimes with no need for the shell protecting core approach.