08 Jul White light LEDs without rare earth elements
The phosphors used in current LEDs almost invariably contain rare earth elements such as europium or cerium. However, extracting these elements is expensive. Above all, they are mined on a large scale in a few regions of the world, primarily in China. This has considerable strategic disadvantages.
Promising transition metal manganese
A research team led by Prof. Dr. Markus Suta from the Inorganic Photoactive Materials working group at Heinrich Heine University Düsseldorf and Prof. Dr. Hubert Huppertz from the Institute of Inorganic and Theoretical Chemistry at the University of Innsbruck has now been looking for alternatives that are more widely available and easier to process. They identified the transition metal manganese (Mn) – more precisely the twofold positively charged manganese ion Mn2+ – as promising. In contrast to the rare earths, manganese is much more widespread in the earth’s crust, it can be easily mined and extracted from the ores, and it is also easy to handle.
But why hasn’t manganese been used for LEDs before? Suta explains: “A fundamental disadvantage is that Mn2+ only absorbs very inefficiently and therefore the luminescence decays relatively slowly. High power densities are therefore necessary to achieve sufficient brightness.” The Mn4+ ion, on the other hand, has already made it into applications, emitting narrow-band red light in fluorides. This is mostly used in displays for monitors. However, the corresponding fluorescent materials are manufactured using hydrofluoric acid, which is a delicate substance to use.
Green and red from one element
The researchers now report on their investigation into the luminescence – the radiation characteristics – of a special compound: the Mn2+ ion in so-called alkali lithosilicates. This class of compounds was already identified a few years ago as potentially promising candidates for cyan-emitting narrowband emitters for displays, but at that time with europium as the emitter.
Suta: “Mn2+ ions emit a narrow-band green glow in the vicinity of four oxygen atoms, but more of a red glow when surrounded by six to eight oxygen atoms. With the right structural details, the brightness of the luminescence remains thermally very stable. This is important, as LEDs with such inorganic phosphors reach operating temperatures of around 150 °C.”
White light LEDs without a rare earth element
Huppertz mentions another advantage: “Together with the blue light of the semiconductor LED, white light can be generated efficiently from available raw materials using a single phosphor.” Two different europium-based phosphors are currently being mixed for this purpose. Suta adds: “This means that a white light-emitting LED with good color tunability can potentially be created.”
A question of power density
The researchers emphasize that the power densities required for excitation must be determined in further investigations. Huppertz says: “We need to see whether the brightness and power consumption of an LED with manganese-activated phosphor based on our concept is actually competitive with today’s LEDs.”
Original publication:
[L. M. Träger, J. I. Ekeya, A. Liesenfeld, M. Wieczorek, H. Huppertz, M. Suta. Mn2+-Activated Alkali Lithooxidosilicate Phosphors as Sustainable Alternative White-Light Emitters. Angew. Chem. 2025, Early View, e202504078; Angew. Chem. Int. Ed. 2025, Early View, e202504078, DOI: 10.1002/anie.202504078]
Source: www.hhu.de
Image: M. Träger et al., Angewandte Chemie International Edition, Wiley-VCH