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

Abstract

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.