We demonstrate print-deposition of high resolution, patterned, multicolored thin films of luminescent colloidal quantum dot (QD)-polymer composites and use the printed patterns in fabricating robust, bright, full-color AC-driven displays. The benefits of AC electroluminescent (EL) displays include simple, low-cost fabrication and high reliability; however, finding efficient and stable phosphors for full-colored displays remains a major challenge.[1] Today, red-, green-, and blue-light-emitting (RGB) phosphors for AC-EL comprise different material systems and can have luminous efficiencies that span an order of magnitude, rendering manufacture of a multicolor display with balanced RGB components difficult. [1][2][3] While there has been substantial research on stacked and patterned devices, one of the most feasible strategies for realizing RGB AC-EL displays is color filtering of white, ZnS-based phosphors. [1,2] Filtering, however, wastes up to 90% of the output optical power to achieve color saturation, which requires that the display be operated at ten times video brightness in order to meet the RGB color standard. [4] This results in greater power consumption, faster pixel degradation, and shorter display lifetimes.[1]To achieve full-color AC-EL displays, in this study we use colloidally synthesized QDs to print patterns of robust, solution-processable, luminescent light-converting thin films for AC-EL displays. QDs offer narrow-band luminescence that can be tuned across the visible spectrum by varying their size and chemical composition. [5] This property motivated the use of QD luminescent centers in thin-film light-emitting diode (LED) structures, in which QDs were electrically excited to demonstrate low-power, color-saturated devices, with side-by-side patterning of RGB pixels enabled by microcontact printing of the QD layers. [6] In alternate device designs, QDs can also be optically excited, where, for example, the small Stokes shift of red-and green-light-emitting QDs enables their optical excitation by blue light. This property of QDs led to the demonstration of optical down-conversion using blue GaN LEDs to excite QDs in polylaurylmethacrylate (PLMA), and the generation of point sources of saturated-color light. [7] In the present work, we demonstrate a planar, full-color AC-EL display that comprises luminescent thin films of QDs that absorb blue electroluminescence from a commercial phosphor powder and then emit photons at a longer wavelength characteristic of the QD band gap. Figure 1. a) Absorption and photoluminescence spectra of spin-coated thin films of red and green QDs and the electroluminescence spectrum of the blue-phosphor paste powered by 50 kHz AC excitation demonstrate the spectral overlaps needed to achieve optical down-conversion of phosphor emission to QD-film luminescence. The inset schematic depicts the crosssection of an AC powder EL device structure with QD-PIB pixels. b) 1 mm profilometry scan of the edge of a green rectangular pixel measuring 3 mm  5 mm demonstrates the edg...

Thin films of polyelectrolyte/J aggregate dye bilayers with high absorption coefficient (6 nm thick with alpha approximately equal to 1.0 x 10(6) cm(-1)) inserted in an optical microcavity enable the cavity quantum electrodynamic strong coupling limit to be reached at room temperature with a coupling strength (Rabi splitting) of 265 +/- 15 meV. By embedding these films in a resonant cavity organic LED structure, we demonstrate the first emissive electrically pumped exciton-polariton device.

The integration of organic and inorganic semiconductors on the nanoscale offers the possibility of developing new photonic devices that combine the best features of these two distinct classes of material. Such devices could, for example, benefit from the large oscillator strengths found in organic materials and the nonlinear optical properties of inorganic species. Here we describe a novel hybrid organic/inorganic nanocomposite in which alternating monolayers of J-aggregates of cyanine dye and crystalline semiconductor quantum dots are grown by a layer-by-layer self-assembly technique. We demonstrate near-field photon-mediated coupling of vastly dissimilar optical excitations in the two materials that can reach efficiencies of up to 98% at room temperature. By varying the size of the quantum dots and thus tuning their optical resonance for absorption and emission, we also show how the ability of J-aggregates to harvest light can be harnessed to increase the effective absorption cross section of the quantum dots by up to a factor of ten. Combining organic and inorganic semiconductors in this way could lead to novel nanoscale designs for light-emitting, photovoltaic and sensor applications.

in 2-1 electrolytes. The model fitting to the experimental data allows us to extract two independent parameters,« and /exptl. The growth behavior of micelles in 2-1 electrolytes is quite different from that in 1-1 electrolytes. The divalent counterions Mg2+ and Ca2+ are more effective in the shielding of electrostatic interactions between micelles than the monovalent counterion Li+. The effective micellar surface charges are strongly affected by the added 2-1 electrolytes when the detergent concentration is low. The measured /exptl is in reasonable agreement with the EMN theory.The mechanism which is responsible for switching the intermicellar interaction from a repulsive to an attractive one is probably due to the gradual dominance of the van der Waals interaction as the double layer repulsion diminishes, and a further investigation on the nature of this attraction should be of great interest.13Acknowledgment. We are grateful to the Biology Department of BNL for use of their small angle spectrometer in this work. Acknowledgement is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this work.

A (5.1+/-0.5) nm thick film of high oscillator strength J-aggregated dye critically couples to a single dielectric mirror, absorbing more than 97% of incident lambda = 591 nm wavelength light, corresponding to an effective absorption coefficient of (6.9+/-0.7) x 10(6) cm(-1) for (film thickness)/lambda < 1%.