麻豆淫院

Virtually all light-emitting diodes used today require phosphors based on so-called rare-earth elements, which are expensive and challenging to obtain. In a collaborative research project between Heinrich Heine University D眉sseldorf (HHU) and the University of Innsbruck, chemists have now demonstrated that the element manganese is in principle also suitable for such applications.

In their study in the journal Angewandte Chemie International Edition, they show that this approach enables white light to be generated from a single manganese-based phosphor.

Light-emitting diodes (LEDs) are energy-efficient and flexible, making them a key technology for sustainable lighting. Current white-light LEDs typically comprise a blue semiconductor LED, the light of which is then converted by two layers of photoactive materials into green light and red light. Combining these light colors creates the desired white light.

The phosphors used in current LEDs almost all contain rare-earth elements such as europium or cerium. However, obtaining these elements is costly and they are only extracted on a large scale in a few regions around the world, primarily in China. This presents significant strategic disadvantages.

A research team headed by Assistant Professor Dr. Markus Suta (Inorganic Photoactive Materials working group at HHU) and Professor Dr. Hubert Huppertz (Department of General, Inorganic and Theoretical Chemistry at the University of Innsbruck) has now sought alternatives, which are more widely available and easier to handle.

They identified the transition metal manganese (Mn)鈥攎ore precisely the twofold positively charged manganese ion (Mn²⁺)鈥攁s promising. By contrast with rare earths, manganese is much more abundant in Earth's crust, can easily be mined and extracted from ores, and also offers straightforward handling.

So why has manganese not already been used for LEDs in the past? Professor Suta explains: "One fundamental disadvantage is the highly inefficient absorption of Mn²⁺, meaning that the luminescence decays relatively slowly. High power densities are therefore needed to achieve sufficient brightness."

By contrast, the ion Mn⁴⁺ is already in use鈥攊t emits narrow-band red light in fluorides and is mostly used for display screens. However, the production of the corresponding phosphors involves hydrofluoric acid, which is problematic.

In Angewandte Chemie International Edition, the researchers now report on their examination of the luminescence鈥攖he radiation properties鈥攐f a special compound: the Mn²⁺ ion in so-called alkali lithosilicates. The working group headed by Professor Huppertz had already identified this class of compounds as potentially promising candidates for cyan-emitting narrow-band emitters for display screens several years ago, albeit still with europium as the emitter at that time.

Professor Suta states, "In contrast to europium ions, manganese ions are much smaller and more flexible when it comes to the selection of specific coordination geometries. Mn²⁺ ions emit narrow-band green light in proximity to four oxygen atoms, but emit red light when surrounded by six to eight oxygen atoms.

"With the right structural details, the brightness of the luminescence retains a high level of thermal stability, which is important as LEDs with such inorganic phosphors reach operating temperatures of around 150掳C."

Professor Huppertz states, "Together with the blue light of the semiconductor LED, efficient white light can thus be generated using a single phosphor obtained from available raw materials." Two different europium-based phosphors are currently mixed to achieve this.

"This offers the potential to create a white light-emitting LED with wide color tunability," adds Suta.

The researchers stress that further investigations are needed to determine the power densities required for excitation. Professor Huppertz concludes, "We need to see whether the brightness and power consumption of an LED with a manganese-activated phosphor based on our concept can actually compete with current LEDs."