Synthesis and properties of colloidal lanthanide-doped nanocrystals

Colloidal solutions and redispersible powders of nanocrystalline, lanthanide-doped phosphates and vanadates have been prepared in high-boiling coordinating solvents or by hydrothermal means in aqueous solution. Highly crystalline materials were obtained by both methods despite the low temperature of 2008C applied during the synthesis. The materials have been characterized by using high-resolution TEM, powder-XRD, absorption spectroscopy and luminescence spectroscopy. By analyzing line splitting and intensity pattern in the luminescence spectra of the europium-doped samples, we are able to verify that the dopant ions enter the same lattice sites as in the corresponding bulk material. Size-selected samples of hydrothermally prepared lanthanide-doped YVO consist of particles 4 ranging in size from about 10 to 30 nm. The nanoparticles exhibit the tetragonal zircon structure known for bulk material. In the case of LaPO the hydrothermal method yields nanoparticles or nano-fibers (width of about 9 nm) depending on the synthesis conditions, while 4 the synthesis in high-boiling solvents yields colloids with a very narrow size distribution and a mean particle size of 4.5 nm. All LaPO -nanomaterials exhibit the monazite-structure, irrespective of their morphology or size. In all systems investigated, energy transfer 4 between the host and the dopant ions is observed. Upon UV excitation, aqueous colloidal solutions of YVO :Eu nanoparticles show a 4 luminescence quantum yield of 15% at room-temperature. In LaPO :Ce, Tb energy transfer is observed between cerium and terbium ions. 4  2000 Elsevier Science S.A. All rights reserved.