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IIT-G, UK college develop nano meta-grid capable of making LEDs energy-efficient

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GUWAHATI, Aug 7 - A team of researchers from the Indian Institute of Technology (IIT) Guwahati and the Imperial College London, UK, have developed a tailored �meta-grid� of nanoparticles that could make light-emitting diodes (LEDs) brighter, energy-efficient and durable.

�Meta-grid� or �metamaterial grid� is a specifically patterned array or grid of nanoparticles acting as metamaterials which are capable of exhibiting extraordinary optical properties.

Dr Debabrata Sikdar, Assistant Professor at the Department of Electronics and Electrical Engineering of IIT Guwahati, along with Prof Sir John B Pendry and Prof Alexei A Kornyshev from Imperial College London, have developed a nanoparticle meta-grid which needs to be placed at an appropriate location within the epoxy coating of the LEDs for improving their light output.

The findings have been published in �Light: Science & Applications� journal of the Nature Publishing Group.

While prescribing minimal changes to the manufacturing process, the research team has developed the novel scheme of boosting transmission of light generated inside an LED chip across the LED-chip or the encapsulant interface.

This is achieved by reducing reflection loss at the chip or 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 or broadband emission spectrum, besides boosting the LEDs� lifetime by eliminating heating of the chip from unwanted reflections within the chip.

The entire original theoretical framework needed for the invention has been developed in-house and has been tested against standard commercial simulation tools. The research team plans to fabricate a prototype device within one year and corroborate their theoretical predictions with experiments.

�With the continuous advancement in nanofabrication technology, it is now possible to fabricate metallic nanoparticles which are mostly monodisperse or having a very narrow spread. Still, there could always be some randomness in particle size and/or position, flatness of grid, and variation in refractive index due to fabrication error or material defects, which are unavoidable. Effects from most of these inaccuracies can be estimated from our tolerance study and it has shown the robustness of our scheme,� Dr Sikdar said.

He added, �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.�

Sir John, who is with the Department of Physics of 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.�

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IIT-G, UK college develop nano meta-grid capable of making LEDs energy-efficient

GUWAHATI, Aug 7 - A team of researchers from the Indian Institute of Technology (IIT) Guwahati and the Imperial College London, UK, have developed a tailored �meta-grid� of nanoparticles that could make light-emitting diodes (LEDs) brighter, energy-efficient and durable.

�Meta-grid� or �metamaterial grid� is a specifically patterned array or grid of nanoparticles acting as metamaterials which are capable of exhibiting extraordinary optical properties.

Dr Debabrata Sikdar, Assistant Professor at the Department of Electronics and Electrical Engineering of IIT Guwahati, along with Prof Sir John B Pendry and Prof Alexei A Kornyshev from Imperial College London, have developed a nanoparticle meta-grid which needs to be placed at an appropriate location within the epoxy coating of the LEDs for improving their light output.

The findings have been published in �Light: Science & Applications� journal of the Nature Publishing Group.

While prescribing minimal changes to the manufacturing process, the research team has developed the novel scheme of boosting transmission of light generated inside an LED chip across the LED-chip or the encapsulant interface.

This is achieved by reducing reflection loss at the chip or 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 or broadband emission spectrum, besides boosting the LEDs� lifetime by eliminating heating of the chip from unwanted reflections within the chip.

The entire original theoretical framework needed for the invention has been developed in-house and has been tested against standard commercial simulation tools. The research team plans to fabricate a prototype device within one year and corroborate their theoretical predictions with experiments.

�With the continuous advancement in nanofabrication technology, it is now possible to fabricate metallic nanoparticles which are mostly monodisperse or having a very narrow spread. Still, there could always be some randomness in particle size and/or position, flatness of grid, and variation in refractive index due to fabrication error or material defects, which are unavoidable. Effects from most of these inaccuracies can be estimated from our tolerance study and it has shown the robustness of our scheme,� Dr Sikdar said.

He added, �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.�

Sir John, who is with the Department of Physics of 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.�

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