According to foreign media reports, light-emitting diodes (LEDs) are the unsung heroes of the lighting industry. They operate efficiently, dissipate less heat, and last a long time. Now, scientists are working on a new material to make LEDs more efficient and last longer for applications in consumer electronics, medicine and security.
Researchers from the U.S. Department of Energy's (DOE) Argonne National Laboratory, Brookhaven National Laboratory, Los Alamos National Laboratory, and SLAC National Accelerator Laboratory report that they have prepared stable calcium for such LEDs Titanite nanocrystals. Research institutes from the Taiwan region of China also contributed to this research.
Perovskites are a class of materials with special crystal structures that absorb and emit light, making them useful in a range of energy-efficient applications, including solar cells and various detectors.
While perovskite nanocrystals are prime candidates for a new type of LED material, they proved unstable in tests. The team stabilized the nanocrystals in porous structures known as metal organic frameworks, or MOFs for short. Based on Earth-abundant materials and made at room temperature, these LEDs could one day enable lower-cost TVs and consumer electronics, better gamma-ray imaging devices, and even autonomous systems for medicine, security scanning, and scientific research. Power the X-ray detector.
"We solved the stability problem of perovskite materials by encapsulating them in MOF structures," said Xuedan Ma, a scientist at the Center for Nanoscale Materials (CNM) in Argonne, DOE's Office of User Facilities, "Our research shows that this approach enables We can dramatically improve the brightness and stability of the luminescent nanocrystals."
Hsinhan Tsai, former JR Oppenheimer postdoc at Los Alamos University, added: "The interesting concept of incorporating perovskite nanocrystals in MOFs has already been demonstrated in powder form, but this is the first time we have successfully integrated them into the emissive layer of an LED. "
Previous attempts to fabricate nanocrystalline LEDs have been hampered by the degradation of nanocrystals back into undesired bulk phases, which take away the advantages of nanocrystals and diminish their potential as practical LEDs. Bulk matter is made up of billions of atoms. Materials like perovskites are made up of a few to thousands of atoms at the nanoscale and therefore behave differently.
In their new method, the team stabilized the nanocrystals by fabricating them in a matrix of the MOF, like a tennis ball being clamped by barbed wire. They used lead nodes in the framework as metal precursors and halide salts as organic materials. The halide salt solution contains methylammonium bromide, which reacts with the lead in the framework and assembles nanocrystals around lead cores in the matrix. Since the matrix keeps the nanocrystals separate, they do not interact and degrade. The method is based on a one-solution coating method that is much less expensive than the vacuum process that is widely used today to make inorganic LEDs.
MOF-stabilized LEDs can produce bright red, blue and green light and different shades of each light.
"In this work, we demonstrate for the first time that perovskite nanocrystals stabilized in MOFs will create bright, stable LEDs in a variety of colors," said Wanyi Nie, a scientist at the Center for Integrated Nanotechnology at Los Alamos National Laboratory. "We can create different colors, improve color purity and increase photoluminescence quantum yield, a measure of a material's ability to emit light."
The research team used the Advanced Photon Source (APS) -- DOE's Office of Science User Facility in Argonne -- to perform time-resolved X-ray absorption spectroscopy, a technique that allowed them to discover changes in perovskite materials over time. Researchers can track the movement of charges through the material and learn important information about what happens when light is emitted.
"We can only do this with the powerful single X-ray pulse and unique temporal structure of APS," said group leader Xiaoyi Zhang in Argonne's X-ray Science Division, "We can track charged particles in tiny perovskite crystals. s position."
In durability tests, the material performed well under UV radiation, heat and electric fields without degrading and losing its light detection and luminescence efficiency, a key condition for practical applications such as televisions and radiation detectors.
