SrAlSi4N7:Eu2+

The new nitridoalumosilicate phosphor SrAlSi4N7:Eu2+ has been synthesized under nitrogen atmosphere at temperatures up to 1630°C in a radio-frequency furnace starting from Sr metal, α-Si3N4, AlN, and additional Eu metal. The crystal structure of the host compound SrAlSi4N7 has been solved and refined on the basis of single-crystal and powder X-ray diffraction data. In the solid, there is a network structure of corner-sharing SiN4 tetrahedra incorporating infinite chains of all edge-sharing AlN4 tetrahedra running along [001] (SrAlSi4N7: Pna21 (No. 33), Z = 8, a = 11.742(2) Å, b = 21.391(4) Å, c = 4.966(1) Å, V = 12.472(4) Å3, 2739 reflections, 236 refined parameters, R1 = 0.0366). The Eu2+-doped compound SrAlSi4N7:Eu2+ shows typical broadband emission originating from dipole-allowed 4f6(7FJ)5d1 → 4f7 (8S7/2) transitions in the orange-red spectral region (λmax = 632 nm for 2% Eu doping level, 450 nm excitation) with a spectral width of FWHM = 2955 (± 75) cm−1 and a Stokes shift ΔS = 4823 (± 100) cm−1. The luminescence properties make the phosphor an attractive candidate material as red component in trichromatic warm white light LEDs with excellent color rendition properties

Ba2AlSi5N9

Ba2AlSi5N9 was synthesized starting from Si3N4, AlN, and Ba in a radio-frequency furnace at temperatures of about 1725°C. The new nitridoalumosilicate crystallizes in the triclinic space group P1 (no. 1), a=9.860(1) Å, b=10.320(1) Å, c=10.346(1) Å, α=90.37(2)°, β=118.43(2)°; γ=103.69(2)°, Z=4, R1=0.0314. All synthesized crystals were characteristically twinned by reticular pseudomerohedry with twin law (1 0 0, −0.5 −1 0, −1 0 −1). The crystal structure of Ba2AlSi5N9 was determined from single-crystal X-ray diffraction data of a twinned crystal and confirmed by Rietveld refinement both on X-ray and on neutron powder diffraction data. Statistical distribution Si/Al is corroborated by lattice energy calculations (MAPLE). 29Si and 27Al solid-state NMR are in accordance with the crystallographic results. Ba2AlSi5N9 represents a new type of network structure made up of TN4 tetrahedra (T = Si, Al). Highly condensed layers of dreier rings with nitrogen connecting three neighboring tetrahedral centers occur which are further crosslinked by dreier rings and vierer rings. The dreier rings consist of corner-sharing tetrahedra, whereas some of the vierer rings exhibit two pairs of edge-sharing tetrahedra. In the resulting voids of the network there are eight different Ba2+ sites with coordination numbers between 6 and 10. Thermogravimetric investigations confirmed a thermal stability of Ba2AlSi5N9 up to about 1515°C (He atmosphere). Luminescence measurements on Ba2AlSi5N9:Eu2+ (2 mol % Eu2+) with an excitation wavelength of 450 nm revealed a broadband emission peaking at 584 nm (FWHM=100 nm) originating from dipole-allowed 4f6(7F)5d1 → 4f7(8S7/2) transitions

Luminescence of the Narrow-Band Red Emitting Nitridomagnesosilicate Li₂(Ca_1–<i>x</i>Sr_<i>x</i>)₂[Mg₂Si₂N₆]:Eu²⁺ (<i>x</i> = 0–0.06)

The nitridomagnesosilicates Li₂Ca₂[Mg₂Si₂N₆]:Eu²⁺ and Li₂(Ca_1.88Sr_0.12)­[Mg₂Si₂N₆]:Eu²⁺ 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. Ce³⁺-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 X-ray diffraction data revealed that Li₂(Ca_1.88Sr_0.12)­[Mg₂Si₂N₆] crystallizes isomorphic to Li₂Ca₂[Mg₂Si₂N₆]: <i>C</i>2/<i>m</i> [<i>Z</i> = 2, <i>a</i> = 5.5744(2), <i>b</i> = 9.8439(3), <i>c</i> = 6.0170(2) Å, β = 97.2520(10)°, <i>R</i>₁ = 0.021, <i>wR</i>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

Toward New Phosphors for Application in Illumination-Grade White pc-LEDs: The Nitridomagnesosilicates Ca[Mg₃SiN₄]:Ce³⁺, Sr[Mg₃SiN₄]:Eu²⁺, and Eu[Mg₃SiN₄]

The isotypic compounds M­[Mg₃SiN₄] (M = Ca,Sr,Eu) have been synthesized by solid-state reactions in sealed tantalum ampules or in a radio-frequency furnace. The nitridomagnesosilicates crystallize in space group <i>I</i>4₁/<i>a</i> (No. 88). Crystal structures were solved and refined from single-crystal X-ray diffraction data (<i>Z</i> = 16, Ca­[Mg₃SiN₄]:Ce³⁺, <i>a</i> = 11.424(2), <i>c</i> = 13.445(3) Å, R1 = 0.040, wR2 = 0.106; Sr­[Mg₃SiN₄]:Eu²⁺, <i>a</i> = 11.495(2), <i>c</i> = 13.512(3) Å, R1 = 0.036, wR2 = 0.102; Eu­[Mg₃SiN₄], <i>a</i> = 11.511(4), <i>c</i> = 13.552(4) Å, R1 = 0.016, wR2 = 0.039). The nitridomagnesosilicates are isotypic to Na­[Li₃SiO₄], containing a condensed tetrahedra network with a high degree of condensation (i.e., atomic ratio (Mg,Si):N) κ = 1. The crystal structures were confirmed by Rietveld refinement, lattice energy (MAPLE) calculations, and further investigated by ²⁹Si-MAS NMR. Ce³⁺-doped samples of Ca­[Mg₃SiN₄] show yellow emission (λ_max = 530 and 585 nm, fwhm ∼3900 cm^–1 (∼130 nm)), while Sr­[Mg₃SiN₄]:Eu²⁺ exhibits red luminescence (λ_max = 615 nm) with the most narrow red emission of Eu²⁺-phosphors reported in the literature so far (fwhm ∼1170 cm^–1 (∼43 nm)). According to this outstanding narrow red emission, originating from parity allowed 4f⁶5d¹ → 4f⁷ transition in Eu²⁺, Sr­[Mg₃SiN₄]:Eu²⁺ may point the way to the next generation red phosphor materials for application in illumination-grade white pc-LEDs

Nitridomagnesosilicate Ba[Mg₃SiN₄]:Eu²⁺ and Structure–Property Relations of Similar Narrow-Band Red Nitride Phosphors

The nitridomagnesosilicate Ba­[Mg₃SiN₄] 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 UCr₄C₄ structure type (space group <i>P</i>1̅ (no. 2), <i>Z</i> = 1, <i>a</i> = 3.451(1), <i>b</i> = 6.069(5), <i>c</i> = 6.101(4) Å, α = 85.200(7), β = 73.697(5), γ = 73.566(8)°, <i>R</i>_p = 0.0218, <i>R</i>_wp = 0.0290). The crystal structure of Ba­[Mg₃SiN₄] consists of a highly condensed network of (Mg,Si)­N₄ tetrahedra with Ba²⁺ centered inside <i>vierer</i> 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 Eu²⁺ shows promising luminescence properties of λ_em = 670 nm with an fwhm ∼1970 cm^–1. Furthermore, anomalous luminescence phenomena, such as trapped-exciton emission, were identified and considered. Ba­[Mg₃SiN₄]:Eu²⁺ is a further narrow-band red-emitting phosphor and is discussed concerning the structure–property relations of recently reported Eu²⁺-doped nitrides with narrow-band red emission

Group (III) Nitrides <i>M</i>[Mg₂Al₂N₄] (<i>M</i> = Ca, Sr, Ba, Eu) and Ba[Mg₂Ga₂N₄]Structural Relation and Nontypical Luminescence Properties of Eu²⁺ Doped Samples

The isotypic nitridomagnesoaluminates <i>M</i>[Mg₂Al₂N₄] (<i>M</i> = Ca,Sr, Ba,Eu) as well as a novel nitridomagnesogallate Ba­[Mg₂Ga₂N₄] have been synthesized by high-temperature reactions in arc-welded tantalum ampules. The crystal structures were solved and refined using single-crystal X-ray diffraction or powder X-ray diffraction data, respectively. All compounds crystallize in the UCr₄C₄-structure type (space group <i>I</i>4/<i>m</i> (no. 87), <i>Z</i> = 2, Ca­[Mg₂Al₂N₄]: <i>a</i> = 8.0655(11), <i>c</i> = 3.2857(7) Å, <i>wR</i>2 = 0.085 Sr­[Mg₂Al₂N₄]: <i>a</i> = 8.1008(11), <i>c</i> = 3.3269(7) Å, <i>wR</i>2 = 0.084; Eu­[Mg₂Al₂N₄]: <i>a</i> = 8.1539(12), <i>c</i> = 3.3430(7) Å, <i>wR</i>2 = 0.033; Ba­[Mg₂Al₂N₄]: <i>a</i> = 8.2602(9), <i>c</i> = 3.43198(19) Å, <i>wR</i>p = 0.031; Ba­[Mg₂Ga₂N₄]: <i>a</i> = 8.3654(12), <i>c</i> = 3.4411(7) Å, <i>wR</i>2 = 0.031) forming highly condensed anionic networks of disordered (Al/Mg)­N₄ and (Ga/Mg)­N₄ units, connected to each other by common edges and corners. The <i>M</i>²⁺ site is centered in <i>vierer</i> ring channels along [001] and coordinated in a cuboidal surrounding by N. Eu²⁺ doped samples of <i>M</i>[Mg₂Al₂N₄] (<i>M</i> = Ca,Sr,Ba) exhibit nontypical luminescence properties including trapped exciton emission in the red spectral region. These compounds widen the group of novel red-emitting materials such as Ca­[LiAl₃N₄]:Eu²⁺, Sr­[LiAl₃N₄]:Eu²⁺, or Sr­[Mg₃SiN₄]:Eu²⁺. Therefore, deep discussion of the observed anomalous luminescence is essential to understand the correlations between all these materials, which are fundamental to design narrow band luminescence of Eu²⁺ systems

Governing Forest Landscape Restoration: Cases from Indonesia

Forest landscape restoration includes both the planning and implementation of measures to restore degraded forests within the perspective of the wider landscape. Governing forest landscape restoration requires fundamental considerations about the conceptualisation of forested landscapes and the types of restoration measures to be taken, and about who should be engaged in the governance process. A variety of governance approaches to forest landscape restoration exist, differing in both the nature of the object to be governed and the mode of governance. This paper analyses the nature and governance of restoration in three cases of forest landscape restoration in Indonesia. In each of these cases, both the original aim for restoration and the initiators of the process differ. The cases also differ in how deeply embedded they are in formal spatial planning mechanisms at the various political scales. Nonetheless, the cases show similar trends. All cases show a dynamic process of mobilising the landscape’s stakeholders, plus a flexible process of crafting institutional space for conflict management, negotiation and decision making at the landscape level. As a result, the landscape focus changed over time from reserved forests to forested mosaic lands. The cases illustrate that the governance of forest landscape restoration should not be based on strict design criteria, but rather on a flexible governance approach that stimulates the creation of novel public-private institutional arrangements at the landscape level