Colloidal solutions and redispersible powders of nanocrystalline, lanthanide-doped YVO 4 have been prepared via a hydrothermal method at 200 °C. High-resolution transmission electron micrographs of size-selected samples show highly crystalline particles ranging in size from about 10 to 30 nm. The particles exhibit the tetragonal zircon structure known for bulk material. Upon UV excitation of the vanadate host, the energy is transferred to the lanthanide ion and strong luminescence (f-f transitions) is observed. By analyzing line splitting and intensity pattern in the luminescence spectrum of the europium-doped sample, we are able to verify that the dopant ions enter the same lattice site as in bulk material despite the nanocrystalline nature of the sample and the low-temperature synthesis. For YVO 4 :Eu nanoparticles a luminescence quantum yield of 15% at room-temperature was observed.

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 luminescence of pure and europium-doped nanocrystalline YVO 4 and YP 0.95 V 0.05 O 4 and the energy transfer processes in such nanoparticles have been studied by temperature dependent luminescence spectroscopy and luminescence lifetime measurements. The results indicate thermally activated energy transfer between adjacent vanadate groups in YVO 4 at temperatures above 100 K, but energy transfer to europium seems to take place from direct vanadate neighbors only. In contrast to the luminescence decay of europium, the kinetic of the vanadate luminescence strongly depends on the choice of surface capping and solvent, indicating partial quenching of the vanadate emission at surface sites. The strong competition with energy transfer to surface sites seems to be reason for the absence of energy transfer to europium from distant vanadate groups. The latter explains the low room-temperature quantum yield of 15% of YVO 4 :Eu colloids.