Wet-Chemical Synthesis of Doped Colloidal Nanomaterials: Particles and Fibers of LaPO 4 :Eu, LaPO 4 :Ce, and LaPO 4 :Ce,Tb.Lanthanoid-doped LaPO 4 nanomaterials are prepared in the high-temperature monazite phase in two morphologies (particles and fibers) via a low-temperature synthesis. The symmetry of the main dopant site is determined from the Eu 3+ emission to be the same as in bulk LaPO 4 .

Nanocrystals of LaPO 4 :Eu and CePO 4 :Tb with a mean particle size of 5 nm and a narrow size distribution have been prepared by reacting the corresponding metal chlorides, phosphoric acid, and a base at 200°C in tris(ethylhexyl) phosphate. Highly crystalline material was obtained as confirmed by X-ray powder diffraction measurements and high-resolution transmission electron microscopy. Successful doping with europium was evident from the splitting and the intensity pattern of the luminescence lines. Luminescence lifetime measurements were used to confirm doping and energy transfer in both materials. Colloidal solutions of CePO 4 :Tb exhibit an overall luminescence quantum yield of 16%.

Nanoparticles with high photoluminescence quantum yield have been recently considered as possible biolabels and as emitters in optoelectronic devices. Now gram amounts of nontoxic, chemically stable LaPO4:Ce,Tb nanocrystals (see picture) have been obtained in a coordinating solvent. These nanoparticles can be easily redispersed in polar solvents to give scatter‐free colloids that exhibit quantum yields of up to 61 %.

The complete series of all nonradioactive lanthanide phosphates has been prepared in organic solution as ligand-capped nanoparticles. In all cases, well-dispersed particles with mean sizes below 10 nm are obtained. Despite the similar chemical properties of the lanthanides, the growth, the crystal structure, and the mean size of the nanocrystals are found to be strongly affected by the lanthanide ion employed. Very small nanoparticles are obtained for lanthanides for which the lattice energies of the bulk tetragonal xenotime phase and the bulk monoclinic monazite phase are similar. These smaller nanoparticles do not show the expected phase transition from monoclinic to tetragonal and seem to have their own unique crystal structure. Possible explanations for these observations are discussed. Finally, we present the first results on the IR emission of Er 3+ -doped YbPO 4 and (Lu, Yb)PO 4 nanoparticles in solution.

Nanoparticles with high photoluminescence quantum yield have been recently considered as possible biolabels and as emitters in optoelectronic devices. Now gram amounts of nontoxic, chemically stable LaPO4:Ce,Tb nanocrystals (see picture) have been obtained in a coordinating solvent. These nanoparticles can be easily redispersed in polar solvents to give scatter‐free colloids that exhibit quantum yields of up to 61 %.