Shinier, robust and pinchpenny LEDs
New Delhi(India Science Wire).
Light-emitting diodes (LEDs) have replaced the ordinary bulbs and they can
further reduce the energy needs on large scale. Researchers from the Indian
Institute of Technology (IIT), Guwahati and Imperial College London, UK, have
developed a tailored ‘meta-grid’ of nanoparticles that could make
light-emitting diodes (LEDs) even brighter, energy-efficient and durable.
'Meta-grid' or ‘metamaterial grid’ is a specifically patterned array (grid) of
nanoparticles acting as metamaterials, capable of exhibiting extraordinary
optical properties.
Over the years, a significant research
drive towards this objective is in exploring new materials for LED-chip
encapsulation, mostly by deploying either higher refractive index glasses or
epoxy materials incorporated with filler powders or nanoparticle-loaded-epoxy
or engineered epoxy resins, etc. However, these techniques either make the LED
chips bulkier or their fabrication becomes more challenging and less
economically viable for mass production.
To meet the goals the research team has
developed a nanoparticle ‘meta-grid’, which can be placed at an appropriate
location within the epoxy casing of the LEDs, for improving light output from
LEDs. A ‘meta-grid’ is a specially-designed, optimised, two-dimensional array
of specific nanoparticles, of size much smaller than the wavelength of light.
While prescribing minimal changes to the
manufacturing process, the research team has developed this novel scheme of
boosting transmission of light generated inside an LED chip across the
LED-chip/encapsulant interface. This is achieved by reducing the Fresnel
reflection loss at the chip/encapsulant interface, within a fixed photon escape
cone, based on tuning the destructive interference phenomena with help of the
‘meta-grid’. The technique has revealed optimal design parameters for such
meta-grids to produce greater light output over any narrow/broadband emission
spectrum, besides boosting LEDs’ lifetime by eliminating heating of the chip
from unwanted reflections within the chip.
Dr.DebabrataSikdar, Assistant Professor,
Department of Electronics and Electrical Engineering, IIT Guwahati said, “In
this invention, the effects of the ‘meta-grid’ on the standard commercial LEDs,
based on group III–V materials are demonstrated. However, the proposed concept
of enhancing light transmission from an emissive layer to its encapsulant
casing can be extended to other types of light emitting devices hosting an
emissive-layer/encapsulant interface. Generally, our nanoparticle ‘meta-grid’
scheme for enhanced light extraction could potentially cater to a wider range
of optical gadgets, not just semiconductor LEDs.”
Talking about their work, Prof. Sir John B.
Pendry, Department of Physics, Imperial College London, said, “The simplicity
of the proposed scheme and the clear physics underpinning it should make it
robust and, hopefully, easily adaptable to the existing LED manufacturing
process. It is obvious that with larger light extraction efficiency, LEDs will
provide greater energy savings as well as longer lifetimes of the devices”.
The research team includes DrDebabrataSikdar,
Prof Sir John B. Pendry and ProfAlexei A. Kornyshev from Imperial College,
London. The findings have been published in Light: Science & Applications
journal.
(India Science Wire)
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