Quantum Dot Spectrometer...

This artist's impression shows five different types of colloidal quantum dots being deposited onto the detector array of a digital camera. (Courtesy: Mary O'Reilly)

Topics: Applied Physics, Modern Physics, Nanotechnology, Quantum Mechanics, Spectrograph

The first-ever spectrometer made from quantum dots has been unveiled by Jie Bao of Tsinghua University in China and Moungi Bawendi of the Massachusetts Institute of Technology in the US. According to its inventors, the instrument could be produced commercially to be as small, inexpensive and simple as a mobile-phone camera. Such compact spectrometers could find a wide range of applications, from gathering scientific data on space missions to sensors integrated within household appliances.

Spectrometry measures the intensity of light as a function of wavelength and is used to study various properties of light-emitting and light-absorbing substances. This makes it an invaluable analytical technique that is used in a broad range of scientific and technological disciplines. Most spectroscopic techniques involve dispersing light in terms of its wavelength. A prism, for example, can be used to bend light into its constituent wavelengths (colours) and a spectrum can then be acquired using a position-sensitive light detector. Bao and Bawendi have taken a different approach, using quantum dots to create an array of band-pass filters for the light to pass through before it reaches a position-sensitive detector.

Quantum dots are tiny pieces of semiconductor just a few nanometres across. They are sometimes described as artificial atoms because, like atoms, they absorb and emit light at specific wavelengths. Unlike atoms, however, the wavelengths can be tuned by simply adjusting the size of the quantum dot.

Bao hit upon the idea of using quantum-dot materials in spectrometers while investigating their use in solar cells and light detectors. "I realized this material has a very unique property that no other material can match," he says, referring to the simple means of tuning the optical response. With this in mind, he began investigating using large numbers of quantum dots in a new type of spectrometer. By monitoring the light that the dots absorbed, it would be possible to determine relative intensities at various wavelengths in the spectrum of the incident light.

Physics World:
Spectrometer made from quantum dots is compact and low cost, Anna Demming, Nanotechweb.org