Sr[BeSi2 N4 ]:Eu2+ /Ce3+ and Eu[BeSi2 N4 ]: Nontypical Luminescence in Highly Condensed Nitridoberyllosilicates.

M[BeSi2 N4 ] (M=Sr,Eu), crystallizing in the hexagonal space group P6‾ 2c, was synthesized from Sr(NH2 )2 , Be3 N2 , and "Si(NH)2 " in W crucibles under a N2 atmosphere in a radio-frequency furnace. The crystal structure was solved from powder X-ray diffraction data by the charge-flipping method (Sr[BeSi2 N4 ]: a=4.86082(2), c=9.42264(4) Å, Z=2; Eu[BeSi2 N4 ]: a=4.85848(1), c=9.41615(4) Å). M[BeSi2 N4 ] contains a highly condensed rigid network of trigonal planar [BeN3 ] units that are connected to Si2 N7 double tetrahedra by common vertices. M[BeSi2 N4 ] (M=Sr,Eu) are the first examples of nitridoberyllosilicates and are isotypic to the oxoberyllate Sr[Be3 O4 ]. Eu2+ -doped Sr[BeSi2 N4 ] and Eu[BeSi2 N4 ] show orange-trapped exciton emission (λem =605 nm, fwhm ≈126 nm), whereas Ce3+ -doped samples of Sr[BeSi2 N4 ] show nontypical yellowish-orange luminescence. Sr[BeSi2 N4 ] has a large band gap of ≈4.4 eV and shows high chemical and thermal stability. Eu2+ -doped beryllates with regular 4f6 5d1 →4f7 -emission could be interesting for future application in LEDs upon doping with Eu2+ or Ce3+ due to large band gaps, rigid networks, and chemical and thermal stability.