Eu 2+ -as well as Ce 3+ -doped Ba[Li 2 (Al 2 Si 2 )N 6 ] and its related Mg-substituted compounds Ba[(Mg 2-x Li x )(Al 4-x Si x )N 6 ]:Eu 2+ (x = 0-2) with x = 1.6, 1.8 have been synthesized by metathesis reactions in tantalum ampules. Crystal structures were solved and refined from single-crystal X-ray diffraction data. All three compounds crystallize in tetragonal space group P4/ncc (no. 130) (Z = 4, Ba[Li 2 (Al 2 Si 2 )N 6 ]:Eu 2+ : a = 7.8282(4), c = 9.9557(5) Å, R1 = 0.0144, wR2 = 0.0366). Their crystal structures, exhibiting the novel framework topology whj, consist of a highly condensated anionic tetrahedra network of disordered (Li/Mg)N 4 and (Al/Si)N 4 units, connected to each other by common edges and corners. The degree of condensation (i.e. atomic ratio (Al,Li,Mg,Si):N) is κ = 1. The Ba 2+ -position is coordinated eightfold by N 3-in form of a truncated square pyramid. Upon doping with Eu 2+ narrow-band emission in the green to yellow spectral range is observed (λ em = 532 -562 nm, fwhm ∼1962 cm -1 ). Ce 3+ -doped crystals of Ba[Li 2 (Al 2 Si 2 )N 6 ] show blue emission (λ em = 468; 507 nm). According to the tunability of the narrow-band green emission, application in LED-backlight LCDs appears promising.

Oxo-and (oxo)nitridoberyllates show exceptional potential as host lattices for application in illumination grade phosphor converted (pc)LEDs due to their remarkable electronic and structural characteristics, allowing highly efficient narrow-band emission upon doping with Eu 2+ . Sr[Be 6 ON 4 ]:Eu 2+ , the first example of an oxonitridoberyllate phosphor, exhibits narrow-band cyan emission (λ em = 495 nm; full width at half-maximum, fwhm = 35 nm; ≈1400 cm −1 ), comparable to the emission of the oxonitridosilicate BaSi 2 O 2 N 2 :Eu 2+ (fwhm = 35 nm) or a cyan-emitting primary LED (fwhm = 27 nm). Sr[Be 6 ON 4 ]:Eu 2+ reveals a highly condensed rigid 3D network with a remarkably large degree of condensation [i.e., atomic ratio Be:(O,N)] of κ = 1.2 that is achieved by interconnection of highly condensed layers of BeN 4 tetrahedra by Be 2 ON 6 units via common edges. The crystal structure of Sr[Be 6 ON 4 ]:Eu 2+ was solved on the basis of single-crystal and powder XRD data (C2/c, no. 15, a = 13.9283( 14), b = 5.7582(6), c = 4.9908(5) Å, β = 90.195(1)°, Z = 4, R 1 = 0.033, wR 2 = 0.065, GoF = 1.046). Sr[Be 6 ON 4 ]:Eu 2+ shows a close structural relationship to other nitride as well as oxide compounds, and therefore closes a structural gap helping to understand relations in Be-containing solid-state materials. The electronic structure of Sr[Be 6 ON 4 ]:Eu 2+ was characterized by X-ray spectroscopy measurements, supported by density functional theory (DFT) calculations. Due to its excellent emission properties, large band gap, rigid 3D network, as well as chemical and thermal stability, Sr[Be 6 ON 4 ]:Eu 2+ is a promising phosphor to close the cyan gap in efficient high-CRI pcLEDs (CRI, color rendering index).

The nitridomagnesosilicate Ba[Mg 3 SiN 4 ] has been synthesized in an arc-welded Ta ampule. The crystal structure was solved and refined from single-crystal X-ray data and Rietveld refinement on the basis of powder X-ray diffraction data, revealing a distorted triclinic variant of the UCr 4 C 4 structure type (space group P ‾ 1 (no. 2), Z = 1, a = 3.451(1), b = 6.069(5), c = 6.101(4) Å, α = 85.200 (7), β = 73.697 (5), γ = 73.566(8)°, R p = 0.0218, R wp = 0.0290). The crystal structure of Ba[Mg 3 SiN 4 ] consists of a highly-condensed network of (Mg,Si)N 4 tetrahedra with Ba 2+ centered inside vierer ring channels along [100] in a cuboidal coordination by N 3-. From UV/vis-reflectance data a band gap of ~4.0 eV was estimated. Doping with Eu 2+ shows promising luminescence properties of λ em = 670 nm with an fwhm ~1970 cm -1 . Furthermore, anomalous luminescence phenomena, like trapped-exciton emission were identified and considered. Ba[Mg 3 SiN 4 ]:Eu 2+ is a further narrow-band red-emitting phosphor and is discussed concerning the structure-property relations of recently reported Eu 2+ -doped nitrides with narrow-band red emission.

Highly efficient narrow-band red emitting (RE) phosphors are the most desired and requested materials for developing illumination grade phosphor-converted light emitting diodes (pcLEDs). This study presents direct measurements of RE energy levels, critical to the color and efficiency of LED phosphors. For the first time, we experimentally determine the energetic separation of the Eu 5d state and the conduction band, which is the key indicator of quantum efficiency. This was achieved for the next-generation pcLED phosphors Li 2 Ca 2 [Mg 2 Si 2 N 6 ]:Eu 2+ , Ba[Li 2 (Al 2 Si 2 )-N 6 ]:Eu 2+ , and Sr[LiAl 3 N 4 ]:Eu 2+ using resonant inelastic Xray scattering. Band to band and 4f to valence band transitions are directly observed in X-ray excited optical luminescence spectra of Sr[LiAl 3 N 4 ]:Eu 2+ and Sr[Mg 3 SiN 4 ]:Eu 2+ . These techniques are widely applicable and create a comprehensive, experimental picture of the Eu 2+ energy levels in these compounds, leading to a complete understanding of all pertinent electronic processes. This study forms the base needed for a detailed discussion of the structure−property relationships, such as specific atoms, coordination and density of states, underpinning phosphor color and efficiency.

Eu 2+show narrow-band red emission at 638 and 634 nm, respectively, with an emission bandwidth of 62 nm (∼1513 cm −1 ) after excitation in the blue spectral region. Ce 3+ -doped samples show luminescence in the green spectral range (λ em = 540 nm). The compounds were synthesized via solid-state metathesis reaction in Li melts. Refinement of single-crystal Xray diffraction data revealed that Li 2 (Ca 1.88 Sr 0.12 )[Mg 2 Si 2 N 6 ] crystallizes isomorphic to Li 2 Ca 2 [Mg 2 Si 2 N 6 ]: C2/m [Z = 2, a = 5.5744( 2), b = 9.8439(3), c = 6.0170(2) Å, β = 97.2520(10)°, R 1 = 0.021, wR 2 = 0.047]. Crystal composition was checked by EDS and ICP-OES measurements and luminescence properties are compared to state of the art narrow-band red emitting luminophors. On the basis of its narrow-band emission, application of the novel red luminophor in high CRI white pcLEDs is promising.