Kodak Quantum Dots Enable Ink Jet LED Fabrication

Eastman Kodak Company (Rochester, NY) inventor Keith B. Kahen developed a method of forming quantum dot based LEDs using  low cost manufacturing techniques to deposit the LED layers on inexpensive substrates such as glass, plastic, metal foil, or silicon.  According to U.S. Patent 7,615,800, Kodak’s manufacturing method for “all inorganic” light emitting diodes (LEDs) based on quantum dot emitters combines many of the desired attributes of crystalline LEDs with those of organic LEDs while overcoming disadvantages of inorganic LEDs.    

Kodak’s inorganic quantum dot LEDs emitters are formed by low cost deposition techniques and the individual layers show good conductivity performance. Using quantum dots as the emitters in light emitting diodes confers the advantage that the emission wavelength can be simply tuned by varying the size of the quantum dot particle. As such, spectrally narrow (resulting in a larger color gamut), multi-color emission can occur from the same substrate. If the quantum dots are prepared by colloidal methods and not grown by high vacuum deposition techniques then the substrate no longer needs to be expensive or lattice matched to the LED semiconductor system.   

Semiconductor light emitting diode (LED) devices have been made since the early 1960's and currently are manufactured for usage in a wide range of consumer and commercial applications. The layers comprising the LEDs are based on crystalline semiconductor materials which require ultra-high vacuum techniques for their growth, such as, molecular organic chemical vapor deposition. In addition, the layers typically need to be grown on nearly lattice-matched substrates in order to form defect-free layers. These crystalline-based inorganic LEDs have the advantages of high brightness (due to layers with high conductivities), long lifetimes, good environmental stability, and good external quantum efficiencies. The usage of crystalline semiconductor layers that results in all of these advantages, also leads to a number of disadvantages. The dominant ones are high manufacturing costs, difficulty in combining multi-color output from the same chip, the need for high cost and rigid substrates. 

It is an advantage of Kahen's invention to provide a way of forming a light emitting layer, whose emitting species are quantum dots, that is simultaneously luminescent and conductive. The light emitting layer includes a composite of conductive wide band gap nanoparticles and shelled quantum dot emitters. A thermal anneal is used to sinter the conductive nanoparticles amongst themselves and onto the surface of the quantum dots. As a result, the conductivity of the light emitting layer is enhanced, as is electron-hole injection into the quantum dots. To enable the quantum dots to survive the anneal step without a loss in their fluorescent efficiency (since the organic ligands passivating the quantum dots boil away during the anneal process), the quantum dot shells are engineered to confine the electrons and holes, such that, their wavefunctions do not sample the surface states of the outer shell.

It is also an advantage to incorporate the conductive and luminescent light emitting layer in an all inorganic light emitting diode device. The electron and hole transport layers are composed of conductive nanoparticles; in addition, separate thermal anneal steps are used to enhance the conductivities of these layers. All of the nanoparticles and quantum dots are synthesized chemically and made into colloidal dispersions. Consequently, all of the device layers are deposited by low cost processes, such as, drop casting or inkjetting. The resulting all inorganic light emitting diode device is low cost, can be formed on a range of substrates, and can be tuned to emit over a wide range of visible and infrared wavelengths. In comparison to organic-based light emitting diode devices, its brightness should be enhanced and its encapsulation requirements should be reduced.

Catalytic Nanoparticles Can Clean-Up Environment, Thwart Terrorists

By using catalytic and magnetic nanoparticles, two Massachusetts Institute of Technology (Cambridge, MA) researchers have discovered a better way to destroy deadly chemicals found in the environment and that terrorist could use in a attack.

The presence of organophosphate esters (OPE) in industrial and agricultural drain waters, spills, runoffs, and drifts, as well as OPE agent-based chemical munitions that may be released in case of warfare or terrorist attack, pose great risks to human health and the environment. The number of exposures to OPE due to pesticides and insecticides is estimated at some 3,000,000 per year, with the total number of deaths and casualties over 300,000 per year worldwide. U.S. Patent 7,598,199 reveals how these deadly chemicals can be safely and more easily detected and removed from the environment.

T. Alan Hatton and Lev E. Bromberg developed compositions and methods for sorbing and destroying organophosphate chemical agents. To this end, the researchers use finely divided, modified nanoscale metal oxide particles. A suspension of magnetite (Fe3O4) nanoparticles modified with 2-pralidoxime or its polymeric analog, poly(4-vinylpyridine-N-phenacyloxime-co-acrylic acid), catalyzes the hydrolysis of organophosphate compounds at a neutral pH. The oxime-modified magnetite particles serve as a nano-sized particulate carrier with a powerful .alpha.-nucleophile, e.g., an oximate group, immobilized on its surface. The oxime-modified magnetite nanoparticles are colloidally stable at neutral pH and they are readily recovered from the aqueous milieu by high-gradient magnetic separation methods. Advantage can be taken of the superparamagnetic properties of the magnetite particles to separate the catalyst from the reaction medium following use, allowing multiple uses.

The immobilized metal complexes have uses in addition to their use to decontaminate areas contaminated with nerve agents and/or pesticides. For example, the catalytic hydrolysis of nerve agents or pesticides using the nano-compositions can be employed as the operative process step in a detector system wherein the by-products of the hydrolysis reaction, such as hydrogen fluoride, may be subject to measurement to provide an indication of the presence and concentration of a particular phosphate ester in the environment. Additionally, the adsorbent nucleophilic particles may be fabricated in the form of filters, sponges, wipes, powder or any other form suitable for use in a decontamination process. For example, the particles may be used in gas masks, wearable protective garments, air filtration systems, and the like.

Numerous OPE pesticides, insecticides and warfare agents, such as sarin, soman, and VX, in addition to being carcinogenic, act as nerve poisons which may cause cumulative damage to the nervous system and liver. Organophosphorus pesticides and warfare agents are not readily hydrolyzed in aqueous media without applying extremes of pH, heat, or bleach. At present, the decontamination solutions of choice are DS-2 (a non-aqueous liquid composed of diethylenetriamine, ethylene glycol, monomethyl ether, and sodium hydroxide) and STB (super tropical bleach). Although DS-2 is generally not corrosive to metal surfaces, it damages skin, paints, plastics, rubber, and leather materials. STB, while effective, has the same environmental problems as bleaches and cannot be used on the skin. Consequently, personal decontamination equipment typically consists of packets of wipes containing such chemicals as sodium hydroxide, ethanol, and phenol. Hatton and Bromberg’s discovery presents a safer and easier alternative to DS-2.