Green luminescence, as required for ubiquitous white-light LEDs, currently originates mainly from phosphors with the well-known garnet structure. In times of high energy prices and political tensions that may restrict access to certain raw materials, having an alternative with a lower synthesis temperature and different chemical composition would be highly advantageous.
Now, Kilian Rießbeck from the research group of Hubert Huppertz has succeeded in synthesizing the first representatives of a new substance class which, despite a completely different composition, can rival the industrial standard. This breakthrough was made possible by materials from the substance class of lithium rare-earth oxonitridolithosilicates, which crystallize in an entirely new structure type.
Building on the widely recognized results in the field of alkali lithosilicates, researchers from the Department of General, Inorganic, and Theoretical Chemistry developed new formulations and synthesis routes to further advance this substance class. The goal was to integrate nitrogen as an additional anion alongside oxygen, while simultaneously creating optimal conditions within the host lattice for partial substitution by activator ions — which themselves belong to the group of rare-earth metals.
The newly presented structure type proves to be highly versatile and tolerant to substitutions, allowing the successful synthesis of 13 different compounds with this structural motif. Another novelty lies in the activator site, which is coordinated in a square-antiprismatic geometry by four oxygen and four nitrogen anions — a coordination environment that is compared in the publication with previously known ones.
A characteristic feature of these compounds is the layered arrangement of tetrahedra, in which four-membered silicate rings are linked by lithium tetrahedra. To better assess the potential of these new materials, high-resolution and temperature-dependent photoluminescence spectroscopy was carried out in collaboration with Markus Suta from Heinrich Heine University Düsseldorf. These measurements provided deeper insights into the mechanisms responsible for the green luminescence of the materials. Moreover, the results indicate that very high efficiencies can be expected if the phosphor is industrially implemented.
Since the overarching research project was conducted in cooperation with the industrial partner ams OSRAM, a prototype LED using the new phosphor could also be fabricated and characterized — demonstrating that the newly developed materials are indeed competitive with the market-standard garnet phosphors.
The results were published in the renowned journal Advanced Functional Materials and highlighted with a cover image. Further publications on this topic are planned.
Publication: K. M. Rießbeck, M. Seibald, C. Stoll, A. Köbler, M. Suta, H. Huppertz: Ce3+‐Activated Lithium Rare‐Earth Oxonitridolithosilicates: A New Class of LED Phosphors with Similarities to Garnets. Adv. Funct. Mater. 2025, e15406. DOI: 10.1002/adfm.202515406; Cover: 10.1002/adfm.72191