Sr[BeSi₂N₄]:Eu²⁺/Ce³⁺ and Eu[BeSi₂N₄]: Nontypical Luminescence in Highly Condensed Nitridoberyllosilicates

M[BeSi 2 N 4 ] (M=Sr,Eu), crystallizing in the hexagonal space group P 2 c , was synthesized from Sr(NH 2 ) 2 , Be 3 N 2 , and “Si(NH) 2 ” in W crucibles under a N 2 atmosphere in a radio‐frequency furnace. The crystal structure was solved from powder X‐ray diffraction data by the charge‐flipping method (Sr[BeSi 2 N 4 ]: a =4.86082(2), c =9.42264(4) Å, Z= 2; Eu[BeSi 2 N 4 ]: a =4.85848(1), c =9.41615(4) Å). M[BeSi 2 N 4 ] contains a highly condensed rigid network of trigonal planar [BeN 3 ] units that are connected to Si 2 N 7 double tetrahedra by common vertices. M[BeSi 2 N 4 ] (M=Sr,Eu) are the first examples of nitridoberyllosilicates and are isotypic to the oxoberyllate Sr[Be 3 O 4 ]. Eu 2+ ‐doped Sr[BeSi 2 N 4 ] and Eu[BeSi 2 N 4 ] show orange‐trapped exciton emission ( λ em =605 nm, fwhm ≈126 nm), whereas Ce 3+ ‐doped samples of Sr[BeSi 2 N 4 ] show nontypical yellowish‐orange luminescence. Sr[BeSi 2 N 4 ] has a large band gap of ≈4.4 eV and shows high chemical and thermal stability. Eu 2+ ‐doped beryllates with regular 4f 6 5d 1 →4f 7 ‐emission could be interesting for future application in LEDs upon doping with Eu 2+ or Ce 3+ due to large band gaps, rigid networks, and chemical and thermal stability.