Nanoparticles of NaGdF4 doped with trivalent erbium (Er3+) and ytterbium (Yb3+) are prepared by a modified thermal decomposition synthesis from trifluoroacetate precursors in 1‐octadecene and oleic acid. The nanoparticles emit visible upconverted luminescence on excitation with near‐infrared light. To minimize quenching of this luminescence by surface defects and surface‐associated ligands, the nanoparticles are coated with a shell of NaGdF4. The intensity of the upconversion luminescence is compared for nanoparticles that were coated with an undoped shell (inert shell) and similar particles coated with a Yb3+‐doped shell (active shell). Luminescence is also measured for nanoparticles lacking the shell (core only), and doped with Yb3+ at levels corresponding to the doped and undoped core/shell materials respectively. Upconversion luminescence was more intense for the core/shell materials than for the uncoated nanoparticles, and is greatest for the materials having the “active” doped shell. Increasing the Yb3+ concentration in the “core‐only” nanoparticles decreases the upconversion luminescence intensity. The processes responsible for the upconversion are presented and the potential advantages of “active‐core”/“active‐shell” nanoparticles are discussed.

Highly dispersible Tm3+/Yb3+‐doped LiYF4 nanocrystals were synthesized using a thermal decomposition method. Upon excitation with a NIR diode laser (980 nm), the dilute dispersion of the nanocrystals exhibits several strong emissions in regions spanning the deep‐UV to NIR, all originating from a single dopant/sensitizer (Tm3+/Yb3+) combination. The material is envisioned to have potential interests in anti‐counterfeiting, biomedicine and solution‐based scintillation applications.

The luminescence properties of hexagonal sodium gadolinium fluoride nanoparticles co-doped with Ho 3+ and Yb 3+ (NaGdF 4 :Ho 3+ /Yb 3+ ), prepared using a thermal decomposition synthesis route, were evaluated following 980 nm excitation. The synthesized nanoparticles were easily dispersed in nonpolar solvents, showed an extremely narrow particle distribution, and were determined to have a mean diameter of 15.6 ( 1.2 nm. The predominantly green upconversion emission was observed to increase with increasing Ho 3+ concentration due to an enhanced energy transfer (ET) from the neighboring Yb 3+ ions. Post-synthesis, the nanoparticles were dispersed in water via modification of the capping oleic acid (OA) ligand. Upconversion emission intensity was observed to decrease upon dispersion in aqueous media likely due to an increase in nonradiative decay pathways. A total ligand exchange with poly(acrylic acid) (PAA) resulted in slightly more intense upconversion emission relative to oxidation of the OA to azelaic acid.

Tetragonal barium yttrium fluoride (BaYF 5 ) nanocrystals doped with 0.5 mol % Tm 3+ and 15 mol % Yb 3+ (BaYF 5 :Tm 3+ , Yb 3+ ) were synthesized using the thermal decomposition method yielding rectangularshaped nanocrystals (15 nm × 5 nm) that can (up)convert near-infrared light to higher energies such as blue, via a process known as upconversion. The upconversion spectrum of the BaYF 5 :Tm 3+ , Yb 3+ nanocrystals, following excitation with 980 nm, revealed that the upconverted blue emission from the 1 G 4 f 3 H 6 transition was more intense than the infrared 3 H 4 f 3 H 6 emission at high excitation densities (90 W/cm 2 ) contrary to what is normally observed for Tm 3+ /Yb 3+ codoped nanomaterials. On the other hand, the infrared emission dominates at lower excitation densities (15 W/cm 2 ) demonstrating a lack of excited Yb 3+ ions to carry on the upconversion beyond the 3 H 4 excited state to the 1 G 4 excited state. A saturation of the upconversion process was observed in the power dependence studies at excitation densities above 57 W/cm 2 , causing a deviation in the expected number of photons required for the upconversion process. The upconversion properties of BaYF 5 :Tm 3+ , Yb 3+ nanocrystals are elucidated and discussed.

Silica nanoparticles functionalized with beta-cyclodextrin (CD) host molecules (5) have been prepared by reacting carboxylic active ester-terminated silica nanoparticles (4) with CD heptamine. Silica nanoparticles functionalized with glucosamine (6), having similar surface properties as 5 but lacking the host-guest recognition motif, were used to perform blank experiments. The CD-functionalized silica nanoparticles 5 were determined by TEM to be 55 +/- 6 nm in size. They exhibited pH-dependent aggregation, which is explained by the presence of free amino and carboxylic acid groups on the particle surface, which was corroborated by zeta potential measurements. The functionalization with CD was further confirmed by host-guest studies in solution and at CD-functionalized silicon substrates. The addition of an adamantyl-terminated dendrimer, capable of multivalent host-guest binding with CD, led to strong aggregation of the CD particles 5, but not of the glucosamine-functionalized 6. Furthermore, 5 gave strong adsorption to CD monolayers on silicon onto which adamantyl-terminated dendrimers were adsorbed, whereas 6 did not. The good discrimination between dendrimer-covered and uncovered areas of the CD monolayer substrates allowed the directed self-assembly of the silica particles 5 onto dendrimer-patterned areas created by microcontact printing.