The phosphorus nitrides, Mg PN and Zn PN , are wide band gap semiconductor materials with potential for application in (opto)electronics or photovoltaics. For the first time, both compounds were synthesized ammonothermally in custom-built high-temperature, high-pressure autoclaves starting from P N and the corresponding metals (Mg or Zn). Alkali amides (NaNH , KNH ) were employed as ammonobasic mineralizers to increase solubility of the starting materials in supercritical ammonia through formation of reactive intermediates. Single crystals of Mg PN , with length up to 30 μm, were synthesized at 1070 K and 140 MPa. Zn PN already decomposes at these conditions and was obtained as submicron-sized crystallites at 800 K and 200 MPa. Both compounds crystallize in a wurtzite-type superstructure in orthorhombic space group Cmc2 , which was confirmed by powder X-ray diffraction. In addition, single-crystal X-ray diffraction measurements of Mg PN were carried out for the first time. To our knowledge, this is the first single-crystal X-ray study of ternary nitrides synthesized by the ammonothermal method. The band gaps of both nitrides were estimated to be 5.0 eV for Mg PN and 3.7 eV for Zn PN by diffuse reflectance spectroscopy. DFT calculations were carried out to verify the experimental values. Furthermore, a dissolution experiment was conducted to obtain insights into the crystallization behavior of Mg PN .

SrSi2O2N2:Eu2+ is an outstanding yellow emitting phosphor material with practical relevance for application in high power phosphor-converted light-emitting diodes. The triclinic compound exhibits high thermal and chemical stability and quantum efficiency above 90% and can be excited by GaN-based UV to blue LEDs efficiently. We have now discovered a hitherto unknown monoclinic polymorph of SrSi2O2N2, synthesized by solid-state reaction, which is characterized by an alternating stacking sequence of silicate layers made up of condensed SiON3 tetrahedra and metal-ion layers. As proven by single-crystal X-ray diffraction, the arrangement of the silicate layers is significantly different from the triclinic polymorph. The translation period along the stacking direction is doubled in the monoclinic modification (P21, Z = 8, a = 7.1036(14), b = 14.078(3), c = 7.2833(15) Å, β = 95.23(3)°, V = 725.3(3) Å3). TEM investigations in combination with HRTEM-image simulations confirm the structure model. The powder X-ray diffraction pattern shows that the volume fractions of the monoclinic and triclinic modifications are approximately equal in the corresponding powder sample. The emission wavelength of 532 nm (fwhm ∼2600 cm–1) as determined by single-crystal luminescence measurements of the monoclinic phase exhibits a shift to smaller wavelengths by ∼5 nm compared to the triclinic polymorph. Differences of the luminescence properties between the monoclinic and triclinic phase are interpreted with respect to the differing coordination of Eu2+ in both phases. The new monoclinic SrSi2O2N2:Eu2+ polymorph is a very attractive phosphor material for the enhancement of color rendition of white-light pc-LEDs.

Highly efficient phosphor-converted light-emitting diodes (pc-LEDs) are popular in lighting and high-tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra-narrow band blue emitting oxoberyllates AELi [Be O ]:Eu (AE=Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi [(Al Si )N ]:Eu . The oxoberyllates' extremely small Stokes shift and unprecedented ultra-narrow band blue emission with fwhm ≈25 nm (≈1200 cm ) at λ =454-456 nm result from its rigid, highly condensed tetrahedra network. AELi [Be O ]:Eu allows for using short-wavelength blue LEDs (λ <440 nm) for efficient excitation of the ultra-narrow band blue phosphor, for application in violet pumped white RGB phosphor LEDs with improved color point stability, excellent color rendering, and high energy efficiency.

The oxonitridosilicate oxides Y4Ba2[Si9ON16]­O:Eu2+ and Lu4Ba2[Si9ON16]­O:Eu2+ have been synthesized starting from REF3, RE 2O3 (RE = Y, Lu), BaH2, Si­(NH)2, and EuF3 in a radiofrequency furnace at 1550 °C. The crystal structures were solved and refined from single-crystal X-ray data supported with Rietveld refinement on X-ray powder diffraction data. Both compounds are isotypic and crystallize in monoclinic space group P21/c (no. 14) with Z = 4 and a = 6.0756(2), b = 27.0606(9), c = 9.9471(3) Å, and β = 91.0008(8)° for RE = Y and a = 6.0290(3), b = 26.7385(12), c = 9.8503(5) Å, and β = 90.7270(30)° for RE = Lu. The unique crystal structure exhibits a three-dimensional network made up from Q4-type SiN4 and Q3-type SiON3 tetrahedra. Containing 4-fold bridging N[4] atoms in star-shaped units [N[4](SiN3)4] next to N[3], N[2], O[1], and noncondensed oxide ions, the title compounds illustrate the vast structural variety in (oxo)­nitridosilicates. Under excitation with UV to blue light, Y4Ba2[Si9ON16]­O:Eu2+ shows emission in the orange-red spectral range (λmax = 622 nm, full width at half-maximum (fwhm) ≈ 2875 cm–1). Yellow-orange emitting Lu4Ba2[Si9ON16]­O:Eu2+ (λmax = 586 nm, fwhm ≈ 2530 cm–1) exhibits high internal quantum efficiency (IQE) ≈ 85%. This makes Lu4Ba2[Si9ON16]­O:Eu2+ a promising phosphor for low color rendering index (CRI) warm white phosphor converted light emitting diodes (pcLEDs).

The nitridosilicate La 3−x Ca 1.5x Si 6 N 11 :Eu 2+ (x ≈ 0.77) was synthesized in a radiofrequency furnace starting from LaF 3 , La(NH 2 ) 3 , CaH 2 , Si(NH) 2 , and EuF 3 . The crystal structure was solved and refined from single-crystal X-ray data in the tetragonal space group P4bm (no. 100) with a = 10.1142(6), c = 4.8988(3) Å, and Z = 2. Thereby, the so far unknown charge balance mechanism in the system (La,-Ca) 3 Si 6 N 11 , which is necessary as bivalent Ca 2+ substitutes trivalent La 3+ , was clarified. Accordingly, charge balance is achieved by incorporation of Ca 2+ on three cation sites, including an additional third site compared to the homeotypic La 3 Si 6 N 11 structure type. The results are supported by Rietveld refinement on powder X-ray diffraction data as well as energy-dispersive X-ray spectroscopy. Fourier transform infrared spectroscopy indicates absence of N−H bonds. An optical band gap of ≈ 4.0 eV was determined using UV/vis reflectance spectroscopy. The Eu 2+ doped compound exhibits a remarkably narrow emission in the yellow-orange spectral range (λ em ≈ 587 nm, fwhm ≈ 60 nm/1700 cm −1 ). Because of the intriguing yellow-orange luminescence, La 3−x Ca 1.5x Si 6 N 11 :Eu 2+ (x ≈ 0.77) is a promising candidate for application in next-generation amber phosphor-converted light emitting diodes.