Friday, February 13th, 2009

Evident Technologies has announced the issuance of US Patent No. 7,482,059 covering the ability to synthesize a quantum dot with a metal layer which dramatically enhances the brightness and stability of a semiconductor nanocrystal complex. This advance of semiconductor materials science relies on a relatively low-cost colloidal formation processing, instead of needing epitaxial lattice-matching or catalytic growth from wafer surfaces.

“Since I started working at Evident in 2001, I’ve seen our patent portfolio grow to over 70 patents and patents pending, and it’s very exciting work,” stated Adam Peng Ph.D., Senior Scientist. “This patented material already goes into our LED products that you can buy at local retailers, so even my kids can see the impact our science has on products. I’m proud to be part of the Evident team.” For example, compared to typical white LEDs that are really blue inside of a white phosphor layer, Evident’s “Ice” color Evidots actually emit white light (CIE coordinates X: 0.292, Y: 0.318) directly (see figure). The company reports the luminous intensity for standard 30deg view driven by 20mA is typically 2000mcd.

Evident’s patent calls out a semiconductor nanocrystal core, a metal layer, and a shell, all of which may be grown by the pyrolysis of organometallic precursors in a chelating ligand solution or by an exchange reaction using the prerequisite salts in a chelating ligand solution. The chelating ligands are typically lyophilic and have an affinity moiety for the metal layer and another moiety with an affinity toward the solvent, which is usually hydrophobic. The shell removes surface defects, adds strength, and creates compatibility with a range of matrix materials, organic solvents, and water.

Inorganic colloids have been studied for over a century ever since Michael Faraday’s production of gold sols in 1857. Today, we have metrology technologies which allow for the control of quantum dot morphology and composition on an industrial scale. A spokesperson for Evident told BetaSights that the company uses standard commercial manufacturing tooling, and for LED applications could supply, “100s of millions without further increases in capacity or resources.” –E.K.

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