Fig. 1: The distribution of electronic fields (colored) around the pillars of a three-dimensional photonic crystal strongly modifies the spontaneous emission of emitters placed within.
NPG Asia Materials featured highlight
Published online 21 May 2008
Taming the spontaneous
Control over the light emission from nanoparticles can be achieved through the use of photonic crystals.
Nanocrystals made from semiconductor materials—quantum dots—are of interest for optoelectronic applications such as light emitters and solar cells. Researchers from Swinburne University of Technology in Australia now describe an approach that allows direct control over the emission efficiency of these quantum dots.
Light emission from semiconductors occurs via a process known as ‘spontaneous emission’. Similar to radioactive decay, spontaneous emission is a random process, and its efficiency can be characterized in terms of the lifetime of the excited electron state from which light emission originates. This lifetime is influenced by the electromagnetic environment in which the emitter is situated.
Michael Ventura and Min Gu have developed a method for controlling the spontaneous emission of lead selenide quantum dots by embedding them into a photonic crystal structure1. “The ability to control spontaneous emission using photonic crystals has far reaching consequences in fields such as solar cells or low, and even zero-threshold lasing, where emission properties can be tailored as desired,” says Gu. The expectation is to be able to turn off spontaneous emission almost entirely in cases where this would be detrimental to the performance of devices such as solar cells.
In order to engineer the spontaneous emission, Ventura and Gu mixed the quantum dots into a polymer matrix. A high intensity laser was then used to carve a three-dimensional photonic structure out of the composite. The periodic structure of photonic crystals strongly modified the propagation of light through the structure (Fig. 1) and light of certain wavelengths was strongly suppressed. As Ventura and Gu demonstrated, if these so-called band gaps were tuned to the emission wavelength of the quantum dots, then the spontaneous emission was suppressed and the fluorescence lifetime of the quantum dots therefore increased significantly.
However, complete suppression of emission in all spatial directions has not been achieved so far, which limits the efficiency of the present devices. Therefore, Gu emphasises that “the next phase of our work is towards the use of other materials for these photonic crystals to enable complete control of spontaneous emission.”
Reference
- Ventura, M. J. & Gu, M. Engineering spontaneous emission in a quantum-dot-doped polymer nanocomposite with three-dimensional photonic crystals. Adv. Mater. 20, 1329–1332 (2008). | article
Author affiliation
| Michael James Ventura, Min Gu * |
| Centre for Micro-Photonics and Centre for Ultrahigh-bandwidth Devices for Optical Systems, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, P.O. Box 218 Hawthorn, VIC 3122 (Australia) |
| email: Min Gu (mgu@swin.edu.au) |
*Correspondence to Min Gu, Centre for Micro-Photonics and Centre for Ultrahigh-bandwidth Devices for Optical Systems, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, P.O. Box 218 Hawthorn, VIC 3122 (Australia).
This research highlight has been approved by the author of the original article and all empirical data contained within has been provided by said author.
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