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Nano-antennae: Let there be more light

Researchers at the Indian Institute of Science have recently shown that combining two of the building blocks in nanotechnology, quantum dots and nanorods, leads to enhanced light emission properties. This may find applications in novel display screens, photodetectors and solar energy applications.

Quantum dots, which are nanometer sized spheres can produce different colours, depending on their size, when light falls on them. This happens via photoluminescence, which is the property of a material to emit light at a unique frequency (color) when light of the same or a higher frequency falls on it. Thus, displays may be constructed by using three different sizes of quantum dots as R, G, B elements and illuminating them with a single source of light. Quantum dot displays are also advantageous from the miniaturisation perspective compared to the current displays, which use LEDs that have a limit on scaling down.

Writing in Applied Physics Letters, Dr. Tripathi and team show that when densely packed semiconductor quantum dots are sparsely decorated with aligned gold nanorods, the photoluminescence of the device is enhanced. Nanorods are a key component here as they have the property to generate large electric fields when light falls on them. They thus act like nano-antennae. That the nanorods are aligned also makes this assembly sensitive to the polarisation of the light falling on it.

Researchers are always looking for ways to improve the interaction of light and matter, as this will increase the efficiency of many optical devices. In this work, lead by Prof. Basu, the photoluminescence enhancement is a result of the long range interactions in quantum dots enhanced by the nanorods. Put simply, when light falls on the quantum dots they talk to each other via electrical signals, the nanorods act as tiny antennae to boost up these signals and as a result the amount of light output is amplified.

“Our results have enormous prospects for both further fundamental studies as well as application in photo-voltaic and display industries.” said Dr. Tripathi. The sensitivity of their device to the polarisation of the light falling on it may also have potential light sensing applications. We shall however keep a keener eye on any smarter displays that result out of this work.

About the authors

Jaydeep Basu is an Associate Professor at the Department of Physics, IISc. L N Tripathi is presently at the Center for Subwavelength Optics, Department of Physics and Astronomy, Seoul National University, South Korea. Pranay Valson is at FUSION-EP, Erasmus Mundus, Institute of Interfacial Process Engineering and Plasma Technology (IGVP), Universitt Stuttgart, Germany. M Praveena is at the Department of Physics, IISc. Both Tripathi and Pranay were at the Department of Physics before moing abroad.

Contact: Jaydeep Basu. 080- 2293 3281, basu@physics.iisc.ernet.in.

The paper has appeared in the latest issue of the journal Applied Physics Letters. It can be accesses at http://dx.doi.org/10.1063/1.4900521.