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 LaF 3 core−shell nanoparticles in aqueous colloidal solutions, by studying the optical properties of the Eu 3+ 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 5 D 0 → 7 F 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 Eu 3+ concentration of 5 atom % confirms that the LaF 3 matrix has a high crystallinity and that each particle is a single crystal.