Nanocrystals in Glass May Be Suitable for LEDs
Daniel S. Burgess
Researchers at the National Institute of Advanced Industrial Science and Technology in Ikeda, Japan, have developed a sol-gel fabrication technique that enables them to embed semiconductor nanocrystals in a glass matrix. The resulting material displays the physical properties of the glass host and the optical properties of the nanocrystals, suggesting potential applications as a phosphor for LED-based lighting.
Scientists have developed a sol-gel process that enables them to embed semiconductor nanocrystals in a glass matrix. At left, the glass phosphor fluoresces under UV illumination to display the logo of the National Institute of Advanced Industrial Science and Technology and the initials of the New Energy and Industrial Technology Development Organization, the sponsor of the research. At right, a transmission electron microscope image of the glass reveals the nanocrystals dispersed in the matrix, indicated by arrows. Courtesy of Norio Murase.
In a demonstration of the technique that they reported in the Jan. 6 issue of Langmuir, colleagues Norio Murase and Chunliang Li added a solution containing aqueous colloids of CdTe to 3-aminopropyltrimethoxysilane sols with a viscosity of 500 to 1500 mPa·s. After two days in the dark, the mixture had formed 0.2-mm-thick transparent glass with nanocrystals dispersed throughout the bulk.
A spectrographic analysis of the CdTe crystals in solution and in the glass matrix revealed little change in their photoluminescent properties. Efficiencies were 35 percent for 3.4-nm-diameter and 41 percent for 6.2-nm-diameter particles, respectively, in the matrix. Heat-treating the glass at 100 °C increased the hardness of the material to 490 MPa without having an effect on the photoluminescent efficiency of the embedded nanocrystals.
Murase said that the emission efficiency of the glass phosphor is independent of excitation wavelength and that the material should be suitable for use with near-UV LEDs. The researchers hope to present phosphors within two years that are sufficiently stable and bright to be suitable for commercial use.
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