We have found recently that Gallium, confined at an interface with silica, responds dramatically to low power optical excitation when held at temperatures close to its melting point (29.8^oC). Intensities of just a few kW/cm² can reversibly modulate the intensity (by up to 40%) and phase (by as much as several degrees) of reflected light as the result of a light-induced structural transition occurring in a layer of gallium of only a few nm thick. Here, we report that this concept - of achieving a nonlinearity via a light-induced transformation in a confined solid at a temperature close to a phase transition temperature - can also be applied to gallium nanoparticles. We present the transient all-optical switching characteristics of gallium nanoparticle films comprising particles, typically 80 nm in diameter, which were formed directly on the ends of optical fibers using a new light-assisted self-assembly technique. We also report, for the first time, that this light-induced structural transition in gallium confined at an interface with silica underlies a new mechanism for photoconductivity. In our opinion, the exploitation of the light-induced phase transition in gallium may be a means of enabling the development of nanoscale photonic devices.

Self-assembly of monodispersed spherical colloids has been demonstrated as an effective strategy to fabricate three-dimensional photonic bandgap crystals. The major challenge in this field is to control the order, thickness, domain size, crystal orientation, defects, and registry of colloidal crystals. In this paper we describe a Template-Assisted Self-Assembly (TASA) approach to control the orientation of the photonic crystals. The self-assembled crystalline lattice usually has a face-center-cubic (fcc) structure with its (111) planes parallel to the surface of the solid support. In TASA process, we used an array of pyramid-shaped pits etched in a Si (100) wafer as the templates. The pits were fabricated by photolithographic patterning and anisotropic etching. Owing to the 70.6° angular geometry of the pyramid-shaped pits, monodispersed colloids nucleated and grew in a vectorial fashion exclusively within the pits to forma pattern of fcc colloidal crystals with (100) layer planes parallel to the (100) face of the single crystalline Si wafer. The small crystals in silicon pits then served as seeds to define and direct the further growth of the crystal along the direction perpendicular to the substrate. A large, (100)-oriented single crystal of colloids with well-controlled thickness was obtained if the diameter of the colloids matched the separation between adjacent pits, and if the raised edge between adjacent pits was small enough.

We describe two different ideas for novel architectures based on photonic crystals of sub-micron colloids. The first involves the formation of photonic superlattices from colloidal photonic crystals. The superlattice periodicity induces the formation of minibands due to folding of the photonic band structure. This represents the first instance in which mid-gap states have been incorporated into a colloidal photonic crystal via a specifically engineered structural modification. The second idea involves applying the superprism concept to three-dimensionally periodic structures. Near a photonic band edge, the diffraction angle is extremely sensitive to the wavelength and propagation direction of the incident light. We analyze this effect in the context of macroporous polymer thin films formed from colloidal crystal templates.

This paper describes the use of confined self-assembly in organizing monodispersed spherical colloids into face-center-cubic crystalline lattices for photonic crystals applications. Using this method, we were able to conveniently control the thickness, the density and structure of defects, and the orientation of a crystal. Inverse opals of polymers and ceramic materials were also synthesized by templating corresponding precursors against three-dimensional colloidal crystals. As an extension to this method, we also demonstrated the hierarchical self-assembly that involved building blocks with sizes on two different scales, and its application in forming inverse opals.

In this work we investigate with the help of low energy electron scattering, force microscopy and optical spectroscopy the growth of ultrathin p-nP (n=4,5,6) films on mica surfaces. We find conditions under which we obtain on a nanometric scale spatially localized emission and conditions under which the emission is spatially non-localized. The latter case results from continuous films of upright molecules (i.e. with transition dipole moments oriented parallel to the surface normal) whereas the former case is obtained if - under certain growth conditions - films consisting of high-aspect ratio 'needles' of laying molecules with well-oriented transition dipole moments along the surface have been grown. Because of a strong interaction between substrate surface dipoles and induced dipoles along the long molecular axes, the needles form macroscopic domains of almost perfectly mutually parallel aligned entities. The quality of the alignment depends on the length of the molecules.

Physically robust photonic bandgap (PBG) composites based on electrostatically stabilized polymeric colloidal particles are presented. The glass transition (T_g)of the composites can be varied over a large temperature range through the selection of the monomer(s) used to fabricate the composite. Composites with a subambient T_g exhibited a mechanochromic response and were integrated with a peizoelectric actuator to produce a prototype device which exhibited a fully reversible tunable rejection wavelength, capable of a ca. +/- 86 nm (172 nm full range)stop band shift.

We report the use of electronic absorption and magnetic circular dichroism (MCD) spectroscopies to probe the magneto-optical properties of Co²⁺ dopant ions in diluted magnetic semiconductor quantum dots. Emphasis is placed on observation and analysis of the ligand field transitions of the Co²⁺ ions. Because the ligand field transitions may be observed in an energy region where the semiconductor host is transparent, ligand field absorption and MCD spectroscopies serve as excellent site-specific spectroscopic methods for studying the dopant ions within DMS nanocrystals. Cobalt-doped CdS nanocrystals (Co²⁺CdS) prepared in solution by the isocrystalline core/shell method are shown by high-resolution TEM to be of high crystallinity. The ligand field spectroscopy demonstrates substitutional doping of Co²⁺ at Cd²⁺ sites. The MCD spectra show a 10³ enhancement in sensitivity for the Co²⁺ ligand field transitions relative to the CdS bandgap transitions. Saturation magnetization experiments yield optically detected ground state magnetization data for these materials, and show that both the ligand field and bandgap MCD intensities follow S = 3/2 Brillouin saturation behavior associated with the isolated Co²⁺ ions. The ⁴A₂-->⁴T₁(P) ligand field bandshape and the sign of the bandgap MCD feature are analyzed in terms of electronic structural parameters for this material.

Ligand-coated metallic nanoparticles are powerful new materials for nano-electronic and photonics applications. They can be readily synthesized and their stability and solubility allows them to be cast in complex composite materials or self-assembled into quasi-ordered films. We demonstrate that, in the presence of reducing dyes with a large two-photon cross-section and metal salts, it is possible to induce the growth of metal nanoparticles in composite films under optical excitation or irradiation with electrons. We demonstrate further that continuous metal structures can be obtained via laser irradiation of the composites and that, with two-photon excitation, 3D structures can be fabricated. Silver, copper, and gold microstructures have been fabricated via two-photon excitation. The composition of our polymeric precursor is described in detail. In order to achieve highly-homogenous solid-state solutions of nanoparticles dissolved in polyvinylcarbazole (PVK), we have synthesized tailor-made nanoparticles on which we have introduced a mixture of carbazoyl-terminated octylthiol and simple octylthiols.. Preliminary experiments on e-beam lithography show that thin films of nanoparticles doped with suitable dyes and metal salts are efficient precursors form metal structures.

Efficient red electrophosphorescence was achieved from double-layer light emitting devices using osmium (Os) complex doped blends of either poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVK:PBD), or poly(vinyl naphthalene) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVN:PBD) as the emitting layer. Blending PVN with PBD greatly suppresses the electromer emission of PVN. The PVN:PBD blend emanates a short wavelength EL emission peaking at around 375 nm, which well overlaps with the absorption spectra of the Os complexes and ensures very efficient energy transfer to the Os complex dopants. PVK:PBD has and EL emission around 450 nm which does not overlap the absorption bands of the osmium complexes as well and produces devices of lower efficiency, but PVK is a better transport layer and produces brighter devices. The best external quantum efficiency of the double-layer devices was 2.2%, with a photometric efficiency of 1.9 cd/A. The brightest device achieved was 1,400 cd/m².

Encapsulated by highly-fluorinated dendrons, a nonlinear optical chromophore core, which is based on the phenyl-tetracyanobutadienyl (Ph-TCBD) thiophene-stilbene-based NLO chromophore, exhibits a large ~30-40 nm blue shift of the charge-transfer absorption maximum, 20 ^oC higher decomposition temperature, and most impressively, three times higher E-O coefficient. The combination of these appreciable improvements makes the molecular design of dendritic modification as a very promising molecular-engineering for next generation of E-O materials.

We report the design, synthesis, and spectroscopic characterization of polyphenylene-type polymers that can be used to sensitize europium complexes. Although benzophenone is widely studied and characterized, polybenzophenones have not been widely used in photophysical studies. The properties of poly(4'-methyl-2,4-benzophenone) (MB), poly(4'-methyl-2,5-benzophenone) (PB) and poly[2,2'-bipyridine-5,5'-diyl(2,5-didecoxy-1,4-phenylene)] (PBP) are described in this paper. All three polymers have backbones that are similar to polyphenylene. PBP has a bipyridine unit that alternates with a phenyl ring. Benzophenone rings are polymerized with para or meta linkages in PB and MB, respectively. All three polymers have similar emission maxima at 430 nm, but PBP has a higher quantum efficiency of emission. The polymers studied in this paper proved to be of lower energy than what is needed to sensitize many europium complexes. In almost all of the lanthanide complexes the ligands played a major role in the emission properties. This was elaborated in studies done previously. Europium chelates of the two different ligands: di(2-thienoyl)methane (DTM) and di(2-naphthoyl)methane (DNM) proved to be of comparable energies with the polymers studied. Results showed that energy transfer did occur between the polymers and the europium chelates, but the energy transfer was not 100% because residual emission from the polymers was detected.

Ink-jet printing technologies are now being developed and used across a wide spectrum of optoelectronic and microelectronic manufacturing applications, because they provide opportunities both for significant cost reductions in existing components and for new component and device configurations. Examples of cost reductions in existing component configurations include printing of optical epoxies to fabricate precision microlens arrays for micro-mirror-based MEMS optical switches and fluxless printing of solder bumps for flip-chip BGA, μBGA and CSP (chin-scale package) manufacture. The most widely recognized, relatively new application of ink-jet printing has arisen in the manufacturing of PLED (Polymer-LED) displays. Potential uses of these technologies for creating new device and package configurations that provide both higher performance and lower cost include microlens printing directly onto VCSELs or the tips of optical fibers for increasing the efficiency of coupling and solder ball printing for making right-angle electrical connections, in order to enable further miniaturization of optoelectronic packages. Example ofnew device configurations which may be fabricated using these capabilities include chip-level optical switches, transceivers, transmitters and receivers.

The unique features of Up-Converting Phosphor Technology (UPTT) have been demonstrated in several particle-based biological assays in recent years. The core-shell structured up-converting phosphor reagents were developed as ultra sensitive labels for biological detection applications. Submicron yttrium oxysulfide (Y₂O₂S) spheres co-doped with trivalent rare earth ion pairs (RE³⁺), e.g. Yb³⁺-Er³⁺ and Yb³⁺-Tm³⁺, were prepared using homogenous precipitation followed by a series of fluidized bed processes. These particles are capable of emitting intense phosphorescence when excited by 950 or 980 nm infrared diode lasers, possessing anti-Stokes shifts greater than 150 nm. We encapsulated Y₂O₂S:RE³⁺ particles with uniform silica shells to passivate the surface and to enhance the dispersibility. The surface of silica-coated particles was further modified with functionalized silanes to provide desired chemical groups (amino, thiol, or carboxyl) for covalent coupling to biomolecules. The functional group densities of the phosphor reagents were characterized using spectroscopic techniques. Fabricated up-converting phosphor reagents can be attached to biomolecules using standard bioconjugation techniques.

The design, synthesis, and characterization of a series of styryl pyrazine derivatives as chemically responsive fluorophores are reported. These styryl pyrazines were ideal for structure-property relationship studies designed to elucidate the role of molecular symmetry, polarity, planarity and cooperative and competitive intramolecular charge transfer interactions in determining their colorimetric or fluorimetric responses. These fluorophores were designed to exhibit large changes in emission in response to changes in solvent composition or addition of various analyte species. The large solvatochromic and analyte-induced changes in their spectra were related to the nature of molecular polarization upon excitation, as well as stabilization of the excited state by the molecular environment. Several of these molecules shared the structural and electronic features common to quadupolar two-photon chromophores, and were thus expected to function as chemically responsive two-photon fluorophores, as well. Calculations of their second hyperpolarizabilities (γ(-ω;ω,-ω,ω))and comparison to known two-photon molecules showed that these molecules were expected to be exceptional two-photon active molecules.

This document describes the combination of frequency selective surfaces (FSS) with deformable MEMS membranes to form a one-by-two optical switch.

In this paper, results of the first observation of magnetization-induced second-harmonic generation (SHG) in one-dimensional magneto-photonic microcavities are described. Both significant magnetization-induced rotation of second-harmonic wave polarization and magnetization-induced variations of the SHG intensity are detected at the fundamental wavelengths in the vicinity of microcavity mode.

This report will present a new and highly versatile manufacturing technology, Laser Reactive Deposition (LRD^TM) processing, to produce planar glass coatings for planar lightwave circuit (PLC) manufacturing. Planar glasses with a wide range of glass compositions offering various passive and active optical functionalities have been produced using this technology. In particular, LRD^TM processing removes a major bottleneck experienced by existing glass fabrication technologies in the high speed deposition of thick and complex glasses. In LRD^TM processing, instead of depositing atoms or molecules a layer at a time, nanoscale particles produced in situ are used as fundamental building blocks for planar glass fabrication. The significantly larger mass of these nanoscale clusters in comparison to atoms or molecules has enabled a much higher throughput and lower cost. Optical quality glasses are obtained by a subsequent high temperature consolidation process. The nanoscale particle size and narrow size distribution, uniquely offered by LRD^TM processing, are critical for the fabrication of high optical quality planar glass. We have demonstrated in this work that LRD^TM processing can produce high quality doped waveguide glasses such as phosphorous-doped silicate glass and UV photosensitive glasses such as germanium-doped silicate glass. We have also demonstrated the capabilities of LRD^TM processing in controlling refractive index and layer thickness of the waveguide core to achieve single mode light propagation at 1.55 microns. Finally, we will present characterization results on basic parameters including propagation loss, surface roughness, and refractive index and thickness uniformity on 4 inch planar glass wafers deposited using LRD^TM processing.

A new photoacid generator (PAG) is described that can be efficiently activated by two-photon excitation and can be used for high-sensitivity three-dimensional micro-patterning of acid-sensitive media. The molecule has a large two-photon absorption cross section that peaks near 705 nm (δ = 690 x 10^-50 cm⁴ s photon^-1) and a high quantum yield for the photochemical generation of acid (φ_H+ ≈ 0.5). Under near-infrared laser irradiation, the molecule produces acid subsequent to two-photon excitation and initiates the polymerization of epoxides at an incident intensity that is one to two orders of magnitude lower than that needed for conventional ultraviolet-sensitive initiators. The new PAG was used in conjunction with the solid epoxide resist Epon SU-8 for negative-tone three-dimensional microfabrication.

Europium cored complexes may be used as a source of red emission in light emitting diodes. Novel europium cored complexes have been synthesized and incorporated into organic light emitting diodes (OLED's). These complexes emit red light at 615 nm with a full width half maximum (FWHM) of less than 5 nm. The europium complexes consist of one equivalent of europium chelated to three equivalents of a nonsymmetrical β-diketone ligand. The Claissen condensation of a polycyclic aromatic sensitizer and an ester of a fluorinated carboxylic acid create the ligands. The use of a sensitizer such as phenanthrene results in a ligand that has an emission band that directly overlaps with the absorption band of europium. The use of fluorinated chains improves the overall processibility as well as the charge transfer capability of the resulting metal cored complex. The europium core is further encapsulated by the inclusion of an additional polycyclic aromatic compound such as 4, 7 diphenyl - 1, 10 phenanthroline. Emission of 615 nm light is accomplished through excitation of the ligand and efficient Forrester energy transfer to the europium complex. A multiple layer device consisting of a substrate of indium tin oxide, followed by thin layers of BTPD-PFCB (with a thickness of 20nm), a polymer blend containing the europium complex (30 nm), followed by a layer of calcium (50nm) and finally a protective layer of silver (120 nm). The polymer blends were either poly(n-vinyl carbazole)(PVK) or poly vinyl naphthalene (PVN). The device performance was further improved by the incorporation of another lanthanide metal complex. These complexes were based upon similar ligands surrounding gadolinium. In these devices, there is a Dexter energy transfer as well as the Forster energy transfer. For the devices that are based on a PVN:PBD as a polymer host, the lowest turn on voltage was 12.0 volts. The devices that use PVK:TPD devices was 178 cd/m² with an external quantum efficiency of 0.61%.For PVK:TKD the brightness was 116 cd/m² with an external quantum efficiency of 0.048%. Devices that incorporate the gadolinium complexes have the turn on voltage of 5.6 volts. We report a maximum brightness of 201 cd/m² with an external quantum efficiency of 1.0%.

Electric fields in dielectric materials produce dipoles related to the polarizability of the material. In this paper we will present a technique that measures the polarization near a surface. The polarization is induced by a modulated signal applied to the conducting probe used for detection. The polarization dipoles in the surface layers of the material generate an electrostatic attraction between the between the probe and the dielectric material. Using techniques common in non-contact force microscopy these forces can easily be sensed. Remarkably, this measurement technique can be extended to frequencies well above the mechanical resonant frequency of the probe cantilever by utilizing amplitude modulation heterodyning. By rastering the probe over the surface an image of the dielectric properties of the surface can be produced. We expect this technique to be useable up to frequencies of at least 20 GHz and time resolution of less than 100 ps. We present calculations of the forces generated assuming simple probe geometries and also thermal noise that compare favourably with experimental results. The technique has been used in the stroboscopic imaging of an operating 434 MHz surface acoustic wave device. The experiments already completed demonstrate that this technique may be employed to produce images that display the local polarizability of materials at a given frequency. In more detailed studies, regions of interest can be imaged repeatedly, with different frequencies used to produce each image.

Application of a new thermal nano-probe based on the changes of electrical resistivity of a nanometer-sized filament with temperature has been presented for the thermal imaging of microwave power active devices. The filament is integrated into an atomic force scanning probe piezoresistive type cantilever. The novel thermal probe has a spatial resolution better than 80 nm and a thermal resolution of the order of 10^-3 K. The measurements have been successfully performed on a 30 fingers GaAs-MESFET with a maximum power dissipation of 2.5 W. The microwave transistor has been implemented in a circuit in such a way to prevent the undesired microwave oscillations. In this case the power dissipation is equal to the dc power input. The near-field measurements have been compared with three-dimensional finite element simulations. A good agreement between simulations and measurements is achieved.

We present a high-speed silicon wafer metrology tool capable of resolving surface features in the nanometer height range. This tool uses a high performance Shack-Hartman sensor to analyze the wavefront of a beam of light reflected from a silicon wafer surface. By translating the wafer to analyze small portions of the wafer in each camera frame and then continuously piecing the frames together, we can retain sub-millimeter spatial resolution while rapidly analyzing large apertures. This tool is particularly effective for resolving features near the wafer edge. We will describe the measures required to obtain this level of resolution. We also compare data taken with this device to that taken with the National Institute of Standards and Technology X-ray optics Calibration Interferometer (XCALIBIR). Finally, we show measurements of a variety of typical and atypical 200 mm diameter wafer samples.

The analysis of electronic noise has the potential to predict forthcoming catastrophic failure of electronic devices and integrated circuits. This has a particularly important potential in submicron and nanoelectronics.

Metal-insulator core-shell structures have been demonstrated to have interesting and tunable optical properties. Systems previously investigated include silica-capped gold particles and gold shells surrounding silica particles. However, many of the systems studied so far have been spherical (or zero-dimensional). Thus, it would be of interest to look at the synthesis and optical properties of one-dimensional (i.e., rod-like) nanostructures. In this paper, the authors present and discuss the formation and properties of silica and titania nanorods encapsulated with a thin gold shell. Nanorods of silica and titania ~10 μm in length and with diameters ~ 90-200 nm are made by combining sol-gel electrophoresis with a suitable template. After removing the template at high temperature, the surface of the rods is re-hydrolyzed by heating in water. 3-Aminopropyltrimethoxysilane is reacted with the surface hydroxyl groups, self-assembling amine functionality on the surface of the rods. These groups act as anchoring sites for the gold, which forms a thin shell around the oxide nanorod. UV-vis absorbance spectra of these samples are analyzed to determine the relationships between shell thickness, core size, core material and properties.

Cadmium Tungstate is a complex oxide which gains considerable attention as a scintillator material. The material has high radiation hardness and in crystalline form is highly efficient. It is also non-hydroscopic, unlike the more efficient thallium doped NaI crystal. A processing technique utilizing sol gel technology has been successfully applied to this system for the first time to allow for more precise stoichiometry control, as well as to produce thin films more easily and cheaply than other methods. The as-produced material consists of single phase, stoichiometric nano-crystallites of cadmium tungstate and shows photoluminescence at 480nm. The material was characterized by X-ray diffraction, SEM and PL analysis.

Dye-functionalized mesoporous silica has gained considerable attention for use in optical applications. Much interest into the tunable functionality of these small-scale optical materials has been the focus for possible use in lasers, light filters, sensors, solar cells, and photocatalysis. Extensive exploration into functionalizing mesoporous silica has been made using sol-gel methods for incorporating polymeric dyes within the pore channels of the silica network to modify optical properties. However, research so far has been focused on functionalization of mesoporous silica powders or films on dense substrates, limiting applications in practice because of the difficult accessibility of mesopores. In this paper, we studied the development of hierarchically-structured mesoporous silica with chromophore dye molecules covalently linked within the channel walls of pores for the selective adsorption and detection of specific ions and chemical compounds. Hierarchically-structured, unidirectionally-aligned mesoporous silica was synthesized within the pores of polycarbonate membranes by surfactant-assisted sol electrophoretic deposition. After the removal of surfactants from the mesopores, the inner surface of the mesopores was functionalized with silane-containing chromophore molecules through self-assembly. Full coverage of these dye molecules on the surface of the mesopores was anticipated due to the fact that these reactant chromophore molecules, in solution, migrate through the pores. The organic chromophore dye molecules, assembled onto the surface of the mesopores, would have the amino groups exposed to the surface. These groups would have the capability to selectively interact with ions or chemical compounds in solution, for instance lead ions in water. Hence, the absorption spectrum of the chromophore dye molecules attached to the mesopores of silica was altered after exposure to lead ions in solution. In addition, the ion concentration in solution also differed. Such functionalized, hierarchically-structured mesoporous silica would have applications such as membranes for removal of, and sensors for, detecting trace amounts of ions and chemical compounds in water and air.

An approach to metallic photonic crystals is demonstrated by using gold-silica core-shell colloids as the building blocks. The formation of gold-silica core-shell nanoparticles involved a base-catalyzed hydrolysis of precursor TEOS and subsequent condensation of silica onto the surfaces of gold cores. The obtained core-shell colloids were monodispersed in size and their shell thickness could be controlled in the range of a few nanometers to about 500 nm. The core diameter could also be varied from ~5 nm to ~100 nm. The core-shell colloids were then employed as building blocks to self-assemble highly ordered three-dimensional photonic crystals using a non-lithographic method. The photonic band-gap properties were characterized by taking the transmittance and reflectance spectra.

We used a combination of dip-pen nanolithography and scanning optical confocal microscopy to fabricate and visualize luminescent nanoscale patterns of various materials on glass substrates. We show that this method can be used successfully to push the limits of dip-pen nanolithography down to controlled deposition of single molecules. We also demonstrate that this method is able to create and visualize protein patterns on surfaces. Finally, we show that our method can be used to fabricate polymer nanowires of controlled size using conductive polymers. We also present a kinetic model that accurately describes the deposition process.

The fluorescence of single ZnS overcoated CdSe quantum dots (QDs) and dye doped polystyrene spheres (PSs) embedded in the evanescent optical field has been studied using an apertureless near-field scanning optical microscope (ANSOM) operating in non-contact and dynamic-force modes. The fluorescence intensity of an individual QD can be enhanced 5 times when an HF etch-cleaned silicon probe is located over the QD and spatially resolved with ~30 nm full width at half maximum when the ANSOM is operating in non-contact mode. Furthermore, we show that the fluorescence contrast in ANSOM is typically 5 times greater than the above enhancement coefficient. In the case of ANSOM dynamic-force mode, the fluorescence of QDs and PSs depends on the pressure applied by the probe to the sample.

Inkjet printing is familiar as a method for printing ink on absorbent paper. In principle the method can be used to print multilayer devices, but we will then need to be able to control the structure of material deposited onto hard surfaces and to overprint different materials on one another. This paper deals addresses the approaches available to form materials by reaction between successive ink layers. The short diffusion distances allow uniform structures to form instead of interfacial barriers or precipitates that would result on a larger scale. Many aspects of these processes can be compared to those that occur during growth of biological tissues. Thus, biology may be a fruitful source of ideas on how to exploit this technology.

New fluorophores that can be excited using visible or near-infrared radiation are of considerable interest for application in environmental and complex bioassays, where background fluorescence is exacerbated by ultra-violet or blue excitation. Useful labels for biomolecules include infrared emitting semiconductor nanoparticles that can be blue-shifted into the near-infrared and visible through quantum confinement effects, oxides of iron, and rare earth oxides. In this work, the synthesis of 6 nm average diameter lead selenide nanocrystals (well below the Bohr exciton diameter of 92 nm) through a reverse micelle technique; and the synthesis of iron and europium oxides with particles less than 5 nm in diameter by pulsed laser ablation is reported. The europium oxide nanoparticles' emission showed a large Stokes shift (144 nm or 216 nm, depending on excitation wavelength); a narrow, symmetric emission line at 610 nm (FWHM of 8 nm); and long lifetime (300 μs). The Eu₂O₃ nanoparticles, which were coated with silica for functionalization, displayed a greatly enhanced sensitivity over a conventional ELISA (0.025 ng ml^-1 vs. 0.1 ng ml^-1) when run in an atrazine immunoassay.