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Novel Crystal Structure Could Be Used to Build LEDs, Lasers

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The discovery of a one-dimensional crystal structure that is highly photo luminescent could help facilitate the development of novel applications for optoelectronic devices such as LEDs, photovoltaic cells and lasers.

The crystal is an organic-inorganic hybrid metal halide perovskite. Its one-dimensional structure enables strong quantum confinement with the formation of self-trapped excited states that give efficient blue-white light emissions. Broadband bluish white-light emissions peaking at 475 nm, with a large full width at half maximum of around 157 nm, were demonstrated for both the bulk and microscale crystals at room temperature. The bulk single crystals have a photoluminescence quantum efficiency (PLQE) of about 20 percent, while the microscale crystals have a PLQE of about 12 percent.

Biwu Ma Florida State University
Biwu Ma is an associate professor of chemical and biomedical engineering. Courtesy of Bill Lax/Florida State University.

The one-dimensional structure was built by a team at Florida State University, led by professor Biwu Ma, who has been researching organo-metal halide perovskites for the past few years as a way to build highly functioning optoelectronic devices.

“The basic building block of this class of materials is the same, like a Lego piece, with which you can assemble different structures,” said Ma.

These Lego-like pieces can be used to form 3D networks, 2D layers, even 1D chains. The research team synthesized the pieces to build a one-dimensional organic lead bromide perovskite, in which the edge sharing octahedral lead bromide chains were surrounded by the organic cations, forming a bulk assembly of core-shell quantum wires. Millions of the organic-coated wires, stacked together, formed the crystalline bundle.

It is well known that the dimensionality of a crystalline system is critical to the exciton self-trapping, due to exciton–phonon interaction. Lowering the dimensionality to one dimension makes exciton self-trapping easier at any exciton–phonon interaction strength.

The research demonstrates that one-dimensional systems could be useful for exciton self-trapping in order to produce highly efficient below-gap broadband luminescence. The one-dimensional crystal structure could offer a novel route to developing superior light emitters based on bulk quantum materials.

“They are good light emitters,” Ma said. “This research tells us we have the capabilities to develop new structures and these materials have great opportunities for practical applications for devices like LEDs and lasers.”

The research was published in Nature Communications (doi: 10.1038/ncomms14051). 

Photonics Spectra
May 2017
A sub-field of photonics that pertains to an electronic device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer. Electro-optic often is used erroneously as a synonym.
optical materials
Materials that, by virtue of their optical characteristics (i.e. refractive index, dispersion, etc.), are used in optical elements. See crystal; glass; plastic lens.
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