Nanoparticles of LaF 3 doped with Ln 3+ (Ln ) Eu, Er, Nd, and Ho) have been prepared that are dispersible in organic solvents. From the spectrum of Eu 3+ it has been concluded that the dopant ion occupies a La 3+ site. The luminescence decays are fitted biexponentially. A given possible explanation for this is a different probability of nonradiative decay for ions at or near the surface and ions in the core of the particles. The lifetimes of Eu 3+ luminescence at a doping concentration of 5% were 7.7 ± 0.2 and 2.9 ± 0.2 ms, indicative of very high quantum yields. The particles doped with Er 3+ , Nd 3+ , and Ho 3+ are promising materials for polymer-based optical components, because they show luminescence in the telecommunication window (i.e., Er 3+ at 1530 nm, Nd 3+ at 1330 nm, and Ho 3+ at 1450 nm).

Surface-coated nanoparticles of LaF 3 and LaPO 4 doped with the luminescent trivalent lanthanide ions Eu 3+ , Nd 3+ , Er 3+ , Pr 3+ , Ho 3+ , and Yb 3+ have been prepared. These ions emit in the visible and in the near-infrared part of the electromagnetic spectrum. The ions Nd 3+ , Er 3+ , Pr 3+ , and Ho 3+ are the main focus in this research because they show emissions in telecommunication windows. The Yb 3+ ion is of interest because it can be used as a sensitizer for Er 3+ . The Eu 3+ ion has been used as a probe for the structural environment of the luminescent ion. It is shown that these lanthanide ions are incorporated in the inorganic host of the particles and that the particles are dispersable in organic solvents. The luminescent lifetimes of the ions are increased by orders of magnitude compared to organic complexes, with values ranging from several microseconds for Pr 3+ and Ho 3+ , up to about 200 µs for Nd 3+ , and 1 ms for Er 3+ . This increase in the luminescence lifetime is indicative of an effective shielding of the lanthanide ions from nonradiative decay of the excited state by the high-energy vibrations of the solvents and the coordinated organic ligands. A model is proposed to describe the nonexponential behavior of the luminescence decay by quenching from outside the particle. It uses two fit parameters, k R , a parameter describing the luminescence decay rate in the absence of surface quenching, and C, a parameter describing the sensitivity toward quenching. Using this model, the luminescence decays can be fitted very well, and factors influencing the luminescence lifetime like concentration quenching and solvent effects can be described accurately.

The surface of lanthanide(III)-doped LaPO4 nanoparticles was modified by reaction with an alcohol, leading to a covalent bond between the ligand and the particle surface. The surface of lanthanide(III)-doped LaF3 nanoparticles was modified to alter the solubility of the nanoparticles and study the influence of surface effects on the luminescence of lanthanide ions doped in the nanoparticles. The coordinated organic ligands can be modified by a quantitative exchange reaction in solution or by using functionalized ligands during the synthesis. Variation of the ratio of ligand to core reagents had a significant influence on the size of the nanoparticles. Smaller nanoparticles were formed with a higher ligand ratio. The optical properties of these nanoparticles show a strong dependence on nanoparticle size, indicating the influence of quenching probably by CH and OH groups at or near the surface of the nanoparticle cores. The luminescence lifetime of LaF3/Eu nanoparticles varied from 6.5 to 7.4 ms for nanoparticles with an average size of 7.1 to 8.4 nm. A significant reduction of the quenching from the surface of the nanoparticles was obtained by the synthesis of core-shell nanoparticles, in which a shell of LaF3 was grown epitaxially around the doped core nanoparticles. This leads to an increase in the luminescence lifetime of the Eu3+ ion and the observation of emissions from the 5D2 energy level, in addition to emissions from the 5D1 and 5D0 levels. The quantum yield of LaF3/Ce,Tb nanoparticles could be increased from 24 to 54% by the growth of a LaF3 shell around the nanoparticles.

The photostability of semiconductor PbSe nanocrystals (NCs) under different storage conditions and the photoluminescence of PbSe NC films on Si substrates under vacuum and under different atmospheres were investigated. The NCs show a small blue shift in both the emission and absorption spectra when stored in solution. This blue shift is accelerated when the particles are stored in room light compared to when the particles are stored in the dark, which indicates that photooxidation is an important process. The photooxidation process is accelerated by irradiating NC solutions with a 450 W xenon lamp. The photobleaching and appearance of a precipitate are attributed to ligand desorption followed by agglomeration. Reversible O 2induced luminescence quenching was observed on a PbSe NC film on Si substrates, which could be addressed by two mechanisms: indirect quenching by alteration of PbSe charging and neutralization dynamics or quenching through direct interaction of O 2 with the exciton. To improve the photostability of PbSe NCs, PbSe/PbS core/shell NCs using (TOP)S (TOP ) trioctylphosphine) and TMS 2 S (TMS 2 ) bis(trimethylsilyl)) as sulfur sources were prepared. However, PbSe/PbS core/shell NCs did not show an increased stability in solution upon irradiation with a xenon lamp when compared with PbSe core NCs. Either the PbS shell is not able to confine the charge carriers or there is incomplete shell passivation with the PbSe core, and as a result these core/shell NCs have comparable stability.

Colloidal, organic solvent-soluble Ln3+-doped LaVO4 nanoparticles have been synthesized by a precipitation reaction in the presence of (C18H37O)2PS2- as ligand, that coordinates to the surface of the nanoparticles. The materials are well soluble in chlorinated solvent such as chloroform. Energy transfer of excited vanadate groups has been observed for Ln3+ ions that emit in the visible and the near-infrared (Eu3+, Tm3+, Nd3+, Er3+, Ho3+, Dy3+, Sm3+, Pr3+), thus making it a very generic sensitization mechanism. The LaVO4 nanoparticles have a different crystal structure than bulk LaVO4 ones (xenotime instead of monazite), similar to YVO4 nanoparticles. This xenotime crystal structure results in a more asymmetric crystal field around the Ln3+ ions that is advantageous to their luminescence, for it increases the radiative rate constant, thus reducing quenching processes.