Researchers improve quantum-dot performance

Quantum dots - tiny particles that emit light in a dazzling array of glowing colours - have the potential for many applications, but have faced a series of hurdles to improved performance. But an MIT team says that it has succeeded in overcoming all these obstacles at once, while earlier efforts have only been able to tackle them one or a few at a time.

The new quantum dots ''combine all these attributes that people think are important, at the same time," says Moungi Bawendi, the Lester Wolfe Professor of Chemistry. IMAGE: OU CHEN

Quantum dots - in this case, a specific type called colloidal quantum dots - are tiny particles of semiconductor material that are so small that their properties differ from those of the bulk material - they are governed in part by the laws of quantum mechanics that describe how atoms and subatomic particles behave. When illuminated with ultraviolet light, the dots fluoresce brightly in a range of colours, determined by the sizes of the particles.

First discovered in the 1980s, these materials have been the focus of intense research because of their potential to provide significant advantages in a wide variety of optical applications, but their actual usage has been limited by several factors.

Now, research published in the journal Nature Materials by MIT chemistry post-doc Ou Chen, Moungi Bawendi, the Lester Wolfe Professor of Chemistry, and several others raises the prospect that these limiting factors can all be overcome.

The new process developed by the MIT team produces quantum dots with four important qualities - uniform sizes and shapes; bright emissions, producing close to 100 per cent emission efficiency; a very narrow peak of emissions, meaning that the colours emitted by the particles can be precisely controlled; and an elimination of a tendency to blink on and off, which limited the usefulness of earlier quantum-dot applications.

Multicolored biological dyes
For example, one potential application of great interest to researchers is as a substitute for conventional fluorescent dyes used in medical tests and research. Quantum dots could have several advantages over dyes - including the ability to label many kinds of cells and tissues in different colours because of their ability to produce such narrow, precise colour variations. But the blinking effect has hindered their use - in fast-moving biological processes, you can sometimes lose track of a single molecule when its attached quantum dot blinks off.