Reviewed by Lexie CornerMar 10 2025
An international team led by researchers at Penn State and Université Paris-Saclay has gained precise control over light emitted from nanoscale sources embedded in two-dimensional (2D) materials. This development could lead to advancements in ultra-high-resolution displays and ultra-fast quantum computing. The study was published in ACS Photonics.
On the left is an illustration of the experimental setup from this study. Molybdenum diselenide nanodots, represented by red triangles, are embedded in tungsten diselenide and encapsulated by hexagonal boron nitride (hBN) on top and bottom. A focused electron beam, shown in green, in a scanning transmission electron microscope (STEM) is aimed at the structure. The emitted light is collected to generate an intensity map. On the upper right is a dark-field STEM image of the molybdenum diselenide nanodot embedded inside tungsten diselenide. The contour of the nanodot is marked by dotted green lines. On the lower right is an artificially colored light emission intensity map of the same region, with the localized emission from the nanodot visible. Image Credit: Provided by the researchers
Researchers demonstrated how to modulate light emitted by 2D materials by embedding a second 2D material inside them, creating what is known as a nanodot. These nanodots, only a few nanometers in size, can alter the color and frequency of emitted light by adjusting their size.
If you have the opportunity to have localized light emission from these materials that are relevant in quantum technologies and electronics, it's very exciting. Envision getting light from a zero-dimensional point in your field, like a dot in space, and not only that, but you can also control it. You can control the frequency. You can also control the wavelength where it comes from.
Nasim Alem, Associate Professor, Materials Science and Engineering, The Pennsylvania State University
Molybdenum diselenide nanodots were embedded within tungsten diselenide nanodots, both of which are 2D materials. The researchers used an electron beam to induce light emission from the structure. They applied cathodoluminescence, a technique that allowed them to examine the high-resolution light emission from individual nanodots.
By combining a light detection tool with a transmission electron microscope, which is a powerful microscope that uses electrons to image samples, you can see much finer details than with other techniques. Electrons have tiny wavelengths, so the resolution is incredibly high, letting you detect light from one tiny dot separately from another nearby dot.
Saiphaneendra Bachu, Study First Author, The Pennsylvania State University
Bachu, who was the primary doctoral student on the study before earning his doctorate from Penn State in 2023 and becoming a TEM Analysis Engineer at Samsung Austin Semiconductor, contributed to the research.
The team found that smaller nanodots produced a different glow than larger ones. When the dots were less than 10 nm wide, roughly the size of 11 hydrogen atoms in a row, they trapped energy and emitted light with a higher frequency, corresponding to a smaller wavelength.
Alem explains that this phenomenon, known as quantum confinement, occurs when the energy of the dots becomes quantized—when confined in a small enough space that new properties emerge, including altered optical and electronic behaviors. In this case, the researchers confirmed that excitons, fundamental particle pairs, were confined by the nanodots at the interface between tungsten and molybdenum diselenide.
Excitons can transfer energy but have no net charge. They can influence semiconductor behavior, which is vital for devices like computers and smartphones. By controlling excitons within materials, scientists aim to regulate the light emitted from these materials, potentially enabling faster, more secure quantum systems and energy-efficient devices such as higher-resolution displays.
Think about how OLED displays work. Each pixel has its own tiny light source behind it, so you can control the exact color or brightness of each one. This lets the screen show true black and accurate colors like red, green, and blue. If you improve this process, you make the picture much sharper and more vibrant.
Saiphaneendra Bachu, Study First Author, The Pennsylvania State University
The band gap of a semiconductor material, which represents the energy threshold electrons must overcome to emit light, can be adjusted for greater control. A single layer of 2D tungsten diselenide, for example, has a direct band gap, making it more effective at emitting light than its thicker, indirect bandgap counterpart, according to Alem.
Within a family of related 2D materials, such as molybdenum disulfide, tungsten disulfide, molybdenum diselenide, and tungsten diselenide, differences in light emission efficiency and other electronic and optical properties arise due to variations in their band gap energies.
By mixing them—like combining molybdenum diselenide and tungsten diselenide in specific ratios — you can fine-tune the band gap to emit light at a specific color. This process, called band gap engineering, is possible because of the wide variety of materials in this family, making them an excellent platform for studying and creating these light sources.
Saiphaneendra Bachu, Study First Author, The Pennsylvania State University
The researchers intend to expand on this work.
“This is just the tip of the iceberg. By exploring the role of atomic structure, chemistry, and other factors in controlling light emission while expanding on lessons learned in this study, we can move this research to the next level and develop practical applications,” said Alem.
This research was partially funded by the Fulbright Scholar Program, NSF CAREER Award, 2DCC-MIP, and the European Union’s Horizon 2020 Research and Innovation Programs.
Journal Reference:
Bachu, S., et al. (2025) Quantum Confined Luminescence in Two Dimensions. ACS Photonics. doi/10.1021/acsphotonics.4c01739?goto=supporting-info