Innovative materials for phosphor converted white light-emitting diodes are in high demand owing to the huge potential of the light-emitting diode technology to reduce energy consumption worldwide. As the primary blue diode is already highly optimized, the conversion phosphors are of crucial importance for any further improvements. We report on the discovery of the high performance red phosphor Sr[Li₂Al₂O₂N₂]:Eu²⁺meeting all requirements for a phosphor’s optical properties. It combines the optimal spectral position for a red phosphor, as defined in the 2016 Research & Development-plan of the United States government, with an exceptionally small spectral full width at half maximum and excellent thermal stability. A white mid-power phosphor-converted light-emitting diode prototype utilising Sr[Li₂Al₂O₂N₂]:Eu²⁺shows an increase of 16% in luminous efficacy compared to currently available commercial high colour-rendering phosphor-converted light-emitting diodes, while retaining excellent high colour rendition. This phosphor enables a big leap in energy efficiency of white emitting phosphor-converted light-emitting-diodes.

Most of the syntheses in solid-state chemistry are performed at constant pressure of ∼1 atm (about 10⁵ Pa) by the manipulation of the thermodynamic parameters temperature and composition, leading to a rich variety of compounds. In contrast, the additional variation of pressure has remained virtually unexplored, due to the relatively large costs of maintaining high-pressure conditions and the inevitably tiny sample volumes. In the last two decades, technical advances, developed for studying the properties of minerals, have found access into the preparative solid-state chemistry, opening up tremendously large areas to synthesize new materials.

A hitherto unknown synthetic access to alkali lithosilicates, a substance class first described by Hoppe in the 1980s, is reported. With the synthesis and characterization of NaK₇[Li₃SiO₄]₈, a new representative has been discovered, expanding the family of known alkali lithosilicates. Astonishingly, NaK₇[Li₃SiO₄]₈ and the already established alkali lithosilicates Na[Li₃SiO₄] as well as K[Li₃SiO₄] display unforeseen luminescence properties, when doped with Eu²⁺. Na[Li₃SiO₄]:Eu²⁺ exhibits an ultra‐narrow blue, K[Li₃SiO₄]:Eu²⁺ a broadband, and NaK₇[Li₃SiO₄]₈:Eu²⁺ a yellow‐green double emission upon excitation with near‐UV to blue light. Consequently, all of the investigated substances of this class of compounds are highly interesting phosphors for application in phosphor converted LEDs.