Sr₅Al5+xSi21−xN35−xO2+x:Eu²⁺ (x≈0)—A Novel Green Phosphor for White‐Light pcLEDs with Disordered Intergrowth Structure

A novel sialon phosphor is characterized by an unusual silicate framework, built up of edge‐ and vertex‐sharing tetrahedra (orange and green). Owing to pronounced pseudotranslations, the compound is highly disordered. It was investigated in detail by X‐ray diffraction and electron microscopy. Despite the disorder, all Sr atoms (yellow spheres) exhibit very similar coordination spheres, and doping with Eu 2+ results in efficient green luminescence (see inset; Em.=emission, Exc.=excitation, Refl.=reflection). magnified image Sr 5 Al 5+ x Si 21− x N 35− x O 2+ x ( x ≈0) was obtained by high‐temperature synthesis (1600 to 1750 °C). Upon doping with Eu 2+ , the thermally very stable material shows an efficient broadband emission in the green spectral range ( λ max ≈510 nm, FWHM=69 nm) under UV to blue light excitation. The compound exhibits a complex intergrowth structure (space group Pmn 2 1 (no. 31); a =23.614, b =7.487, c =9.059 Å; V =1601.5(6) Å 3 ; Z =2, R 1=0.067), which consists of highly condensed dreier ring layers alternating with sechser ring layers that include both vertex‐ and edge‐sharing (Si,Al)(O,N) 4 tetrahedra. Both layer types exhibit pseudotranslational symmetry, which leads to a more or less pronounced disorder of the sechser ring layers. The Sr atoms are located in channel‐like voids of the silicate framework with coordination number nine. The compound has been characterized by single‐crystal and powder X‐ray diffraction, as well as high‐resolution electron microscopy and electron diffraction. The structure and chemical composition has been confirmed by 29 Si solid‐state NMR spectroscopy, lattice energy calculations, and diverse elemental analyses.