Make particles of semiconductors small enough-just a few nanometers across-and they glow in a dazzling range of colors. These nano particles are known as quantum dots, because quantum effects tune the color of the glow to the size of the particle-a phenomenon that scientists have seized upon to make exquisitely sensitive biomedical assays (see "Quantum Dot Com," TR January/February 2000). In theory, these tiny glowing particles could also be a boon for optical networking by providing lasers and amplifiers that work in a wide range of frequencies. But for over a decade experts have been trying to fashion quantum-dot lasers, with little success.

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