Quantum dots, a class of nanoscale semiconducting particles, are promising for LEDs and other optoelectronics because they efficiently emit light in the visible range (see the article by Dan Gammon and Duncan Steel, Physics Today, October 2002, page 36). To make an LED, researchers must first form the quantum dots into layers or films. But when they are assembled together, the close proximity leads to interdot energy transfer, which dims their luminescence by one to two orders of magnitude compared with an isolated dot. Similarly, many other nanomaterials lose some of their desirable properties when they are built into three-dimensional materials.

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