Multiple wavelengths of light emitted from a single source using carbon nanoparticles

Changing the photoluminescence of dual color emitting carbon (CD) droplets depending on their concentration. Blue and red emissions show different contributions with different inter-particle distances. Credit: KAIST

KAIST researchers have synthesized a collection of nano-particles, known as carbon droplets, capable of emitting multiple wavelengths of light from a single particle. Furthermore, the team found that the distribution of carbon droplets, or the interparticle distance between each point, affects the light properties that carbon droplets emit. The discovery will allow researchers to understand how to control these carbon droplets and create new, environmentally responsible displays, lighting technology and sensation.

Research into nanoparticles capable of emitting light, such as quantum dots, has been an active area of ​​interest for the past half-decade. These particles, or phosphors, are nano-particles made of different materials that are capable of emitting light at specific wavelengths utilizing the quantum mechanical properties of materials. This provides new ways to develop lighting and display solutions, as well as more accurate detection and sensing in instruments.

As technology becomes smaller and more sophisticated, the use of fluorescent nanoparticles has seen a dramatic increase in many applications due to the purity of the colors they emit from the dots, as well as their suitability to meet the desired optical properties.

Carbon droplets, a type of fluorescent nanoparticle, have seen an increase in interest from researchers as a candidate to replace non-carbon droplets, the construction of which requires heavy metals that are toxic to the environment. Since they are composed mainly of carbon, low toxicity is an extremely attractive quality when coupled with the adjustability of their inherent optical properties.

Another striking feature of carbon droplets is their ability to emit multiple light wavelengths from a single nanoparticle. This multi-wavelength emission can be stimulated under a single excitation source, enabling the simple and strong generation of white light from a single particle by emitting multiple wavelengths simultaneously.

Carbon droplets also exhibit a concentration-dependent photoluminescence. In other words, the distance between individual carbon droplets affects the light that the carbon droplets then emit under a source of excitation. These combined properties make carbon droplets a unique resource that will result in extremely accurate detection and sensation.

This concentration dependence, however, was not fully understood. In order to make full use of the capabilities of carbon droplets, the mechanisms that regulate seemingly variable optical properties must first be discovered. It was previously theorized that the dependence of the carbon droplet concentration was due to a hydrogen bonding effect.

Now, a KAIST research team, led by Professor Do Hyun Kim of the Department of Chemical and Biomolecular Engineering has presented and demonstrated that dual color emission is due to cross-particle distances between each carbon point. The research was published in 36th The issue of Physical Chemistry Chemical physics.

The first author of the paper, PhD candidate Hyo Jeong Yoo, along with Professor Kim and researcher Byeong Eun Kwak, examined how the relative light intensity of red and blue colors changed as the interparticle distances, or concentration, of points changed of carbon. They found that as the concentration was adjusted, the light emitted by the carbon droplets would be transformed. By changing the concentration, the team was able to control the relative intensity of the colors as well as emit them simultaneously to generate a white light from a single source (See Figure).

“The dependence of the concentration of photoluminescence of carbon droplets on the change of emission origin for different interparticle distances has been overlooked in previous research. By analyzing the phenomenon of dual-color emission of carbon droplets, we believe this result could provide a new perspective to investigate their mechanism of photolumination, “explained Yoo.

The newly analyzed ability to control the photoluminescence of carbon droplets is likely to be widely used in the continuous development of solid state lighting and sensitivity applications.

Reference: “Interparticle distance as a key factor in controlling the dual emission properties of carbon points” by Hyo Jeong Yoo, Byeong Eun Kwak and Do Hyun Kim, June 25, 2020, Physical Chemistry Chemical physics.
DOI: 10.1039 / D0CP02120B

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