Luminescence D 6540Highly Efficient Multicolor Upconversion Emission in Transparent Colloids of Lanthanide-Doped NaYF4 Nanocrystals. -Transparent colloidal solutions of Yb/Er and Yb/Tm doped NaYF4 nanocrystals exhibit bright upconversion emission in the red, green, and blue spectral region by excitation around 1 µm with a laser of moderate power. These new systems show a substantial improvement on the order of 10 8 compared to previously reported systems. -(HEER, S.; KOEMPE, K.; GUEDEL, H.-U.; HAASE*, M.; Adv.

The growth of NdPO4 nanocrystals in diphenyl ether based reaction medium has been monitored by optical spectroscopy. Since the crystal field splitting and the intensity of the Nd3+ f−f transitions are affected by the coordination of the Nd3+ ions, different stages of the growth of NdPO4 nanocrystals can be distinguished by UV−visible absorption spectroscopy. It is found that a first reaction in homogeneous solution occurs already at room temperature when the phosphate-containing precursor solution is combined with the solution of the molecular Nd3+ precursor. Our results clearly indicate that a sol of NdPO4 nanoparticles with a mean particle diameter below 3 nm is thereby formed as the first product. Upon heating to 200 °C, this first product undergoes a complex sol−gel−sol transition, leading to a colloidal solution of 4−5 nm diameter NdPO4 nanocrystals. Further heating at 200 °C leads to annealing of the nanocrystalline lattice, but not to further particle growth if the amine concentration is sufficiently high.

Near-infrared (NIR) marker-based imaging is of growing importance for deep tissue imaging and is based on a considerable reduction of optical losses at large wavelengths. We aim to extend the range of NIR excitation wavelengths particularly to values beyond 1.6 μm in order to profit from the low loss biological windows NIR-III and NIR-IV. We address this task by studying NIR-excitation to NIR-emission conversion and imaging in the range of 1200 up to 2400 nm at the example of harmonic Mg-doped lithium niobate nanoparticles (i) using a nonlinear diffuse femtosecond-pulse reflectometer and (ii) a Tunable hIGh EneRgy (TIGER) widefield microscope. We successfully demonstrate the existence of appropriate excitation/emission configurations in this spectral region taking harmonic generation into account. Moreover, NIR-imaging using the most striking configurations NIR-III to NIR-I, based on second harmonic generation (SHG), and NIR-IV to NIR-I, based on third harmonic generation (THG), is demonstrated with excitation wavelengths from 1.6–1.8 μm and from 2.1–2.2 μm, respectively. The advantages of the approach and the potential to additionally extend the emission range up to 2400 nm, making use of sum frequency generation (SFG) and difference frequency generation (DFG), are discussed.

The steric position of the methoxy group in different isomers of methoxycinnamic acid ligands is observed to have a strong impact on the particle growth of lanthanide phosphate nanoparticles. Very small nanoparticles with a mean size of less than 4 nm are obtained for all phosphates from lanthanum to europium, if 3-methoxycinnamic acid or trans-4-methoxycinnamic acid are used as ligands or if these methoxy isomers are replaced by cinnamic acid or phenylpropionic acid. However, if trans-2-methoxycinnamic acid is employed in the synthesis, anisotropic particle growth along the [200] axis is observed, yielding elongated nanoparticles with an average length of up to 25 nm. Our results indicate that in all cases small nanoparticles are formed first at early stages of the synthesis and that these particles grow to larger particles only if trans-2-methoxycinnamic acid is used as the ligand. We assume that the position of the methoxy group in trans-2-methoxycinnamic acid leads to an easier displacement or removal of these ligands from the surface of the small particles, resulting in a less effective shielding of the particles against particle growth.

Luminescence Luminescence D 6540 Synthesis, Growth, and Er 3+ Luminescence of Lanthanide Phosphate Nanoparticles. -The complete series of all nonradioactive lanthanide phosphates is synthesized in gram amounts in organic solution from hydrated LnCl3 and tributyl phosphate as ligand-capped nanoparticles. The samples are characterized by powder XRD, TEM, and SAXS. The growth, crystal structure, and the mean size of the nanocrystals are strongly affected by the lanthanide ion employed. First results on the IR emission of Er 3+ -doped YbPO 4 and (Lu,Yb)PO 4 nanoparticles in solution are given. In toluene both colloids show Er 3+ emission at about 1550 nm either via direct excitation of the Er ions at 378 nm or after excitation of the Yb ions at 980 nm. -(LEHMANN, O.; MEYSSAMY, H.; KOEMPE, K.; SCHNABLEGGER, H.; HAASE*, M.; J. Phys.

Yield. -The title core-shell nanoparticles are prepared from a MeOH solution of CePO4:Tb nanoparticles, H3PO4 in dihexyl ether, and LaCl3·7H2O (200°C, yield given in g). Growth of the LaPO4 shell around the core particles increases the quantum yield of the Tb emission to 70% and the total quantum yield to 80%. These reproducible values are not far from the quantum yield of the bulk material, which is 86% for the Tb emission and 93% for the total emission. The quantum yield of these nanoparticles can probably be further increased by optimizing the thickness of the shell and by employing metal salts of very high purity. -(KOEMPE, K.; BORCHERT, H.; STORZ, J.; LOBO, A.; ADAM, S.; MOELLER, T.; HAASE*, M.; Angew.

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In-vivo tracking based on harmonic nanoparticles is so far not exploited because of a lack on an appropriate tool. Here we present a new approach based on the re-design of the laser space parameters.