Conformational characterization of Eu3+-doped LaF3 core-shell nanoparticles through luminescence anisotropy studies

Polarization techniques have been implemented to determine the size and shape of LaF3 core-shell nanoparticles in aqueous colloidal solutions, by studying the optical properties of the Eu3+ active ion inserted as a dopant in the core of the nanoparticles. A luminescence anisotropy as high as 0.4 has been measured for the D-5(0) -> F-7(0) transition with the sample frozen in a glass water-glycerol matrix. Time-resolved luminescence anisotropy at different temperatures and viscosity of the medium indicated that the particles present a mainly spherical shape and a size distribution very close to 10 nm. The absence of depolarization by energy transfer for a Eu3+ concentration of 5 atom % confirms that the LaF3 matrix has a high crystallinity and that each particle is a single crystal.