Development of nanophosphors for light emitting diodes.

We report the development of new nanophosphor structures based on the Mn-doped ZnSeS material system to enhance the color properties, luminosity and efficiency of white LEDs. These structures have been demonstrated for phosphor-based white LED applications utilizing both blue and UV LED systems. Bandgap tuning for near UV (405 nm) and blue (460 nm) excitations are reported. Using various optimization procedures, we have produced ZnSe:Mn nanoparticles with an external quantum yield greater than 80%.

Direct visualization of optical frequency invisibility cloak based on silicon nanorod array.

A new invisibility cloak was recently proposed for hiding objects in front of a highly reflecting mirror. This cloak requires only modest values of optical constants with minimal anisotropy and thus can be implemented by using non-resonant dielectric materials, making it an ideal system for optical frequency operation. We implemented the cloak using an array of silicon nanorods fabricated by electron-beam lithography. We then directly visualized the cloaking effect by monitoring the light propagation inside the device using the near-field optical microscopy.

Electron-phonon interactions in ce3+-doped yttrium aluminum garnet nanophosphors.

Ce 3+-doped yttrium aluminum garnet nanophosphors with sizes near 30 and 250 nm have been synthesized by using chemical gelation and solvothermal methods, respectively. The size-dependent electron-longitudinal-optical-phonon coupling is investigated by fitting measured photoluminescence spectra within the framework of the Brownian oscillator model. Results show that the coupling strength is in a decreasing order from the bulk material to the nanophosphors of much smaller sizes.

Polarization beam splitter based on a photonic crystal heterostructure.

The design and characterization of a photonic crystal (PC) polarization beam splitter (PBS) that operates with an extinction ratio of greater than 15 dB for both polarizations are presented. The PBS is fabricated on a silicon-on-insulator (SOI) wafer where the input and output ports consist of 5 mum wide ridge waveguides. A large spectral shift is observed in the dispersion plots of the lowest-order even (TE-like) and odd (TM-like) modes due to the SOI confinement. Because of this shift, the TE-like mode is close to a directional gap at the top of the band, and the TM-like mode is in a low-frequency regime where the dispersion surface is almost isotropic. We show that the TE-like mode has very high reflection at the interface between the two PCs, whereas the TM-like mode exhibits a very high transmission.

Nonspherical ZnS colloidal building blocks for three-dimensional photonic crystals.

The asymmetry introduced by a complex or nonspherical basis promotes photonic band gap formation in three-dimensional photonic crystals. However, relatively few techniques have been demonstrated to produce uniform nonspherical colloids for use as photonic crystal bases. Here we expand the menu of basis types with high refractive index by preparing nonspherical zinc sulfide colloids of uniform size and shape. Dimers, trimers, and planar tetramers were precipitated from aqueous solution by the thermal decomposition of thioacetamide in the presence of zinc nitrate, manganese nitrate, and nitric acid. The well-defined morphological types were obtained from suspensions aged for 4-6 h at 26-32 degrees C and then for 20-35 min at 85 degrees C. Stereological techniques were used to analyze SEM images and determine the percentage of each particle class. For example, the quantitative characterization of a particle population prepared at 29 degrees C for 6 h and 85 degrees C for 22 min had the composition 59+/-3% spheres, 31+/-2% dimers, 7+/-1% trimers, 0.4+/-0.2% tetramers, and 2.5+/-0.8% complex clusters (encompasses all other varieties of shape). X-ray diffraction and X-ray photoelectron spectroscopy confirmed the zinc blend crystal structure and the stoichiometric composition of the particles. The refractive index was estimated as 2.25 (413 nm) -2.09 (709 nm) by fitting experimental absorption spectra to curves derived from Mie scattering calculations. This indicated an average porosity approximately 24%. Such colloids offer the potential to form diamond-like lattices with large, stable photonic band gaps.

The (homo)sexual temptation in Milton's Paradise regained.

While the sexual temptation of Paradise Regained is tactful, it is also characteristically Miltonic in its daring. Despite its decorous presentation, the temptation is exceedingly bold in that it is not merely a heterosexual temptation but a homosexual one as well. Acknowledgement of the homosexual lure in the brief epic is essential to understanding the dynamics of the celebrated banquet scene and to appreciating the comprehensiveness of Milton's trial of the Son's humanity. Such a recognition also helps place in perspective the alleged misogyny of Paradise Regained, even as it also reveals the complexity of Milton's poetic technique, particularly his ability to work by indirection and implication and to exploit classical and biblical sources. Although Jesus rejects the homosexual temptation (as He does the heterosexual one), He does not condemn homosexuality. Milton's incorporation of a homosexual temptation provides evidence of his sophisticated recognition of the range of fully human sexual responses.

Practical infection control in oral health surveys and screenings.

Examinations for oral health surveys and screenings are performed by dentists or dental hygienists in a variety of settings. To date, CDC has made no recommendations for infection control specifically for these brief examinations. General principles for infection control can be applied during oral health surveys and screenings.

Direct measurement of the effective refractive indices of GaAs/AIGaAs slab waveguides: a new technique.

A new method is presented for accurately and nondestructively measuring the effective refractive indices of GaAs slab waveguides. The experimental setup is extremely simple. This method is particularly applicable for buried waveguides and high refractive index waveguides that cannot be measured by prism couplers. It is also suitable for glass and LiNbO(3) waveguides.

A factor analysis of traits as measured by COCSTOC-MOT to identify occlusal trait combinations.

Occlusal conditions which vary significantly from accepted social norms for dental appearance may socially handicap an individual. An instrument is required by which socially unacceptable occlusal conditions can be identified by members of the public who have internalized society's norms for acceptable dental appearance. The factors identified in this paper make it possible to select a reasonable number (100) of models for constructing a measurement instrument which depicts the full range of occlusal patterns found in a natural population for use in assessing the social acceptability of occlusal conditions. This paper presents the methodology and process used to identify individual occlusal traits which tend to occur together in trait combinations or independently and their range from "normal" to extreme. Data on the frequency distribution of the individual COCSTOC measurements found in a natural population was subjected to a factor analysis which identified 18 occlusal patterns (combinations of traits) and five unique or independent traits or anomalies.

Scanned-laser microscope for photolurminescence studies.

A scanned-laser microscope has been developed to generate photoluminescence maps, or images, of semiconductor samples. This instrument is shown to be extremely useful for evaluating semiconductor wafers, especially those intended for light-emitting diodes. The design and construction of this new microscope are discussed, and performance tests of a prototype are presented. The photoluminescence microscope achieves a spatial resolution near 10(-3) cm with a spectral definition of 100 A and examines an area 0.6 cm on a side in a few seconds. Examples of the application of the photoluminescence microscope to testing of GaAsP wafers are presented and compared with the results of other kinds of tests to determine the suitability of these wafers for light-emitting diodes.