Tunable Luminescence in an Oxonitride Phosphor - ACS Publications

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SrAl2−xLi2+xO2+2xN2−2x:Eu2+ (0.12 ≤ x ≤ 0.66)Tunable Luminescence in an Oxonitride Phosphor Gregor J. Hoerder,† Simon Peschke,‡ Klaus Wurst,† Markus Seibald,‡ Dominik Baumann,‡ Ion Stoll,§ and Hubert Huppertz*,† †

Institute of General, Inorganic, and Theoretical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria OSRAM Opto Semiconductors GmbH, Mittelstetter Weg 2, D-86830 Schwabmünchen, Germany § OSRAM Opto Semiconductors GmbH, Leibnizstrasse 4, D-93055 Regensburg, Germany Downloaded via NOTTINGHAM TRENT UNIV on September 5, 2019 at 00:26:42 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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S Supporting Information *

ABSTRACT: Starting from the recently published narrow band red phosphor SALON, a tunable oxonitride-phosphor can be derived by introducing disorder into the structure. To achieve this, the oxygen content of the reaction mixture is increased, thereby prohibiting the oxygen/nitrogen ordering observed in SALON. The resulting compound is isotypic to UCr4C4 and exhibits mixed oxygen/nitrogen and lithium/aluminum sites. Further variation of the oxygen/nitrogen ratio revealed that the structure remains stable over a wide range of compositions. The compound can therefore be described by the general sum formula SrAl2−xLi2+xO2+2xN2−2x with x ranging between 0.12 and 0.66. When doped with Eu2+, the title compound exhibits an intense luminescence upon excitation with blue light. The maximum of this emission varies depending on the oxygen content and can be tuned to values between 581 nm (x = 0.66) and 672 nm (x = 0.12).

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Lu, Y),16 and Sr4[LiAl11N14]:Eu2+,17 some of which have since found their way into application. Especially interesting with regard to this publication is the recently published high performance narrow band red phosphor SALON (SrLi2Al2O2N2:Eu2+)18 as it can be described as an ordered variant of the here presented SrAl2−xLi2+xO2+2xN2−2x. While many nitride compounds exhibit similar structures, to the best of our knowledge SALON is the only example of an UCr4C4like structure in an oxygen rich oxonitride. Remarkably, SrAl2−xLi2+xO2+2xN2−2x still exhibits the same overall connectivity, although it does not show the ordering effect present in SALON. Despite their close structural relation, the luminescence properties of the two compounds differ dramatically as SALON exhibits an extremely narrow bandwidth of 48 nm with an emission maximum located at 614 nm, while SrAl2−xLi2+xO2+2xN2−2x exhibits a much broader emission with maxima between 581 and 672 nm, depending on the exact composition of the sample. The tunable emission of

INTRODUCTION In modern pcLED lighting devices, a primary LED is combined with a layer of one or more different luminescent materials in order to achieve the desired quality of light. These phosphors define the spectral characteristics of the device and are therefore a key-component of the LED technology. Since LEDs are becoming more and more prevalent, much research has been dedicated toward finding and optimizing new phosphors.1−7 Although there are many other substance classes, such as quantum dots and manganese-doped fluorides, which can be used as phosphors in LEDs, rare earth doped ceramic materials are still by far the most commonly used type of LED phosphor.8−10 They exhibit a variety of desirable properties, such as high stability and a broad absorption in the blue spectral region, which is needed in order to absorb the light emitted by the LED chip. Especially Eu2+ doped compounds have been studied extensively over the past few years, which led to the discovery of many new phosphors such as M[Mg3SiN4]:Eu2+ (M = Sr, Ba, Ca, Eu),11,12 Sr[LiAl3N4]:Eu2+,13 Ca[LiAl3N4]:Eu2+,14 NaK7[Li3SiO4]8:Eu2+,15 RE4Ba2[Si12O2N16C3]:Eu2+ (RE = © XXXX American Chemical Society

Received: May 21, 2019

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DOI: 10.1021/acs.inorgchem.9b01479 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Luminescence Measurements. The title compound’s singlecrystal emission signal was measured by exciting a single-crystal with a 460 nm laser (model Sapphire 460/10, 10 mW; COHERENT, USA). The converted light was collected using a multimode optical fiber (QP 600-2-VIS/BX; Ocean Optics, USA) and finally detected in a spectrometer (QE 65000; Ocean Optics, USA). The excitation spectrum and the powder emission spectra were collected on a Fluoromax 4 spectrophotometer (HORIBA, Japan) on compacted powder pellets. The excitation was measured in the range between 320 and 600 nm with a 1 nm step size while the emission was monitored at 605 nm. The emission spectra were measured in the wavelength range between 430 and 780 nm with a step size of 1 nm using an excitation wavelength of 460 nm and an integration time of 0.2 s per step. The quantum efficiency (number of converted photons/number of absorbed photons in %) was measured using a QUANTAURUS-QY spectrometer (Hamamatsu, Japan) equipped with a full integrating sphere (diameter approximately 8.4 cm) and a 150 W xenon excitation light source with excitation at 500 and 450 nm. pc-LED Prototype. Prototype LEDs were manually cast using 5 wt %, 10 wt %, 20 wt %, and 40% of the SrAl2−xLi2+xO2+2xN2−2x:Eu2+ (x ≈ 0.6) phosphor material in a commercially available low refracting index silicone. Reference LEDs were manually casted using commercially available α-SiAlON21−23 using 5%, 10%, 18%, and 23 wt % of the phosphor material in a commercially available low refracting index silicone. LEDs were built using a standard OSRAM Golden DRAGON LED package (λdom = 450 nm, 960 μm2 emitting surface area). Measurements were carried out with an in-house-built system based on an integrating sphere (ISP150) coupled to an Instrument Systems Compact Array Spectrometer (CAS-140B) at an operating current of 200 mA. The data were collected in a pulsed mode with 5 ms settling time and 20 ms integration time at 25 °C.

SrAl2−xLi2+xO2+2xN2−2x can be advantageous, as it can be adapted to fit a variety of different applications. In an oxonitride system, the luminescence properties can be tuned via the nephelauxetic effect and the crystal field splitting by variation of the oxygen/nitrogen ratio. For this approach, the phosphors overall structure must remain uninfluenced by the substitution, as the luminescence properties would change abruptly during a phase transition. In this work, we report on the synthesis and characterization of SrAl2−xLi2+xO2+2xN2−2x:Eu2+, an oxonitride phosphor closely related to SALON.18 It exhibits an emission which can be tuned via the oxygen/nitrogen ratio while retaining its structure over a wide range of compositions.

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EXPERIMENTAL SECTION

Synthesis. Two different synthetic routes were used to obtain the title compound. One to receive bulk samples and one optimized for single-crystal growth. For the preparation of the bulk samples, different mixtures were used consisting of either SrCO3 (Solvay, HP SL300) or SrO (derived from SrCO3 via calcination at 1280 °C), Al2O3 (Sinochem Hebei, 99.99%), AlN (Tokuyama, E-Grade), Li2CO3 (Alfa Aesar, 99%), and Li3N (Materion, 99.5%) in ratios according to the desired stoichiometry with Eu2O3 as doping agent. Ten to 20 g of these mixtures were homogenized and filled into a Ni-crucible, which was then placed into a tube furnace and fired to 725−800 °C under a constant N2-stream. The temperature was maintained for 4−8 h. Heating and cooling were conducted at rates of 250 °C/h. Bulk samples could be obtained for nominal compositions between x = 0.12 and x = 0.66. For the synthesis of single-crystals, all manipulations were carried out using an argon filled glovebox (UNIlab Plus Glove Box Workstation, MBraun, Garching, Germany; O2 < 1 ppm, H2O < 1 ppm). SrAl2−xLi2+xO2+2xN2−2x was synthesized using Sr3Al2O6 (97.34 mg, 0.236 mmol, synthesized according to the method by Garcés et al.19) and LiN3 (23.09 mg, 0.472 mmol, synthesized according to the method by Fair et al.20) as well as Eu2O3 (0.83 mg, 0.002 mmol, Smart Elements, 99.99%) as doping agent. The starting materials were mixed in an agate mortar and placed into a tantalum ampule, which was weld shut utilizing tungsten inert gas welding. During the welding process the ampule was water-cooled to avoid an unwanted decomposition of the lithium azide. The closed ampule was then placed into a silica tube, which was evacuated to prevent the oxidization of the tantalum container. This silica tube was placed into a tube furnace and heated to 900 °C. The sample was maintained at this temperature for 24 h and subsequently cooled to 500 °C with 0.1 °C per minute. Upon reaching 500 °C the furnace was turned off and the sample was left to cool down to room temperature. The product was obtained in the form of orange crystals with some AlN as a side phase. The synthetic procedure is very similar to the synthesis of the SALON phosphor as the two compounds have an almost identical composition. Much like the SALON phosphor, SrAl2−xLi2+xO2+2xN2−2x is not stable against direct water exposure, yet stable enough to be used in LED prototypes. Powder X-ray Diffraction. Powder X-ray diffraction patterns were collected using an Empyrean powder diffractometer (Panalytical, Netherlands) with Cu Kα1 radiation (λ = 154.06 pm). Single-Crystal X-ray Diffraction. Single-crystals were isolated from the sample under a microscope and glued to a glass wire. The diffraction data was collected using a Bruker D8 Quest diffractometer with monochromatic Mo Kα radiation (λ = 71.073 pm) and a Photon 100 CMOS detector. Images for the visualization of the structure were created using the DIAMOND 3.2k application. The crystallographic information file may be obtained from the Cambridge Crystallographic Data Centre, CB2 1EZ Cambridge (+44 (0)1223 336408, https://www.ccdc.cam.ac.uk), on quoting the deposition number 1912154.

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RESULTS AND DISCUSSION

Crystal Structure. The crystal structure of the title compound, Sr[Al2−xLi2+xO2+2xN2−2x], was solved and refined based on single-crystal X-ray diffraction data obtained from one representative crystal with x ≈ 0.5 (Figure 1).24 It crystallizes isotypically to UCr4C4 in the tetragonal space group I4/m (no. 87) with the lattice parameters a = 7.8588(5) Å and c = 3.1844(3) Å (for details see Table 1 and Table S1/

Figure 1. Overview of a 2 × 2 × 2 supercell of Sr[Li2.5Al1.5O3N] viewed along the c-axis. Red spheres represent strontium-atoms, blue/ green spheres oxygen/nitrogen-atoms, and the Al/Li centered tetrahedra are depicted in yellow. B

DOI: 10.1021/acs.inorgchem.9b01479 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Crystallographic Data for Sr[Li2.5Al1.5O3N] Empirical formula Formula weight/g mol−1 Temperature/K Crystal system Space group a/Å c/Å Volume/Å3 Z ρcalc/g cm−3 μ/mm−1 F(000) Crystal size/mm3 Radiation 2Θ range for data collection/deg Index ranges Reflections collected Independent reflections Data/restraints/parameters Goodness-of-fit on F2 Final R indices (I ≥ 2σ(I)) Final R indices (all data) Residual electron density/e Å−3

Sr[Li2.5Al1.5O3N] 207.45 294(2) tetragonal I4/m 7.8588(5) 3.1844(3) 196.67(3) 2 3.503 13.898 192 0.050 × 0.04 × 0.03 Mo Kα (λ = 0.71073 Å) 7.334 to 59.928 −11 ≤ h ≤ 10, −11 ≤ k ≤ 11, −4 ≤ l ≤ 4 2345 168 [Rint = 0.0331, Rσ = 0.0128] 168/0/15 1.169 R1 = 0.0370, wR2 = 0.1011 R1 = 0.0373, wR2 = 0.1014 2.104/−0.582

Figure 2. Details from the crystal structure of Sr[Li2.5Al1.5O3N]. Top left: strand of edge sharing tetrahedra. Top right: Coordination of the strontium cation. Bottom: Channel running along the c-axis.

S2 in the Supporting Information). Due to the relatively low nominal europium content of 2% and its therefore insignificant influence on the scattering power, the europium was neglected during the structure refinement. There are three crystallographic sites within the structure. One is hosting the strontium cations, while the other two each exhibit a statistically mixed occupancy. One mixed site is occupied by nitrogen and oxygen, the other by aluminum and lithium atoms. The Al/Liatoms are coordinated by four O/N atoms forming a slightly distorted tetrahedral coordination sphere. Each tetrahedron is connected to two other tetrahedra via common edges resulting in endless strands along the c-axis of the structure (Figure 2, top left). These strands are interconnected via common corners resulting in a rigid 3D-framework where each O/N-site acts as a 4-fold bridging position. This results in a sphaleritelike degree of condensation κ, which is equivalent to the atomic ratio of (Li,Al)/(O,N) = 1. As a result of the connection between the strands, channels are formed along the c-axis of the structure (Figure 2, bottom). Every second channel is slightly larger and occupied by the strontium cations. These cations are coordinated by eight equidistant O/ N-sites (Sr-(O/N) = 2.674(4) Å) forming a cubelike coordination sphere (Figure 2, top right). The Eu2+ activator is assumed to partly replace the strontium cations in the structure, as the ionic radii of Eu2+ (1.39 Å) and Sr2+ (1.40 Å) are nearly identical.25 Powder Diffraction. Bulk samples of SrAl2−xLi2+xO2+2xN2−2x were investigated by powder X-ray diffraction. The Rietveld analysis, which is displayed in Figure 3, is in good agreement with the structure obtained from the single-crystal refinement. It revealed the sample to consist mostly of the title compound (87.2 wt %) as well as SrO (12.8 wt %), which is present as a byproduct. For details on the refinement please refer to Table S3 in the Supporting Information. Using the Rietveld refinement, the lattice parameters of products with different nominal compositions (x = 0.12−0.66)

Figure 3. Rietveld plot of a bulk sample. Experimental data (black), pattern obtained from refinement of Sr[Li2.5Al1.5O3N] (red), and difference curve (blue). The reflexes of SrO are marked with blue crosses.

were determined. The results ranged between 7.85 and 7.91 Å for a, and 3.18 and 3.21 Å for c, leading to cell volumes between 196.37 Å3 and 201.42 Å3. This clearly indicates that the composition follows the nominal Al/Li and O/N content. Luminescence. Luminescence investigations were carried out on the crystal used for the single-crystal structure refinement as well as on bulk samples with various compositions. The emission of the single-crystal has its maximum at ≈578 nm and exhibits a fwhm (full width at half-maximum) of 80.0 nm (2380 cm−1). It compares well with the bulk measurement exhibiting the same lattice parameters with only a slight blue shift due to reabsorption effects within the bulk sample (see Supporting Information Figure S1). Therefore, the luminescence properties of the bulk sample can clearly be associated with SrAl2−xLi2+xO2+2xN2−2x (0.12 ≤ x ≤ 0.66). This also rules out the possibility that SrO, which is present as a side phase in the bulk sample of C

DOI: 10.1021/acs.inorgchem.9b01479 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry SrAl2−xLi2+xO2+2xN2−2x and can exhibit a red emission when doped with Eu2+, contributes to the observed emission spectra.26 Since it has been shown that the reduction of Eu3+ is often not quantitative,27 additional emission measurements have been performed to exclude the possible contribution of residual Eu3+ to the luminescence. The spectra collected with excitation wavelengths of 250−350 nm (10 nm steps) did not show any Eu3+ emission, proving that there is no contribution of Eu3+ to the observed emissions. The excitation spectrum of SrAl2−xLi2+xO2+2xN2−2x:Eu2+, which is displayed in Figure 4, shows a broadband absorption between roughly 350 and 500 nm enabling efficient excitation by blue light.

Figure 6. Emission spectra of bulk samples with different nominal compositions exemplifying the shift of the emission maximum. Black curve (λmax = 581 nm, x = 0.66), blue curve (λmax = 605 nm, x = 0.60), green curve (λmax = 629 nm, x = 0.44), orange curve (λmax = 642 nm, x = 0.32), and red curve (λmax = 672 nm, x = 0.12).

up to a fwhm of 105 nm (2610 cm−1, 1.91 eV) for the spectrum peaking at 642 nm (x = 0.32). Samples with lower xvalues show a decrease in fwhm leading to a value of 100 nm (2220 cm−1, 1.84 eV) for the emission peaking at 672 nm (x = 0.12). This may be due to a preferential occupation in the structure foreshadowing the ordering observed in SALON.18 All displayed spectra have been collected using the same measurement parameters and were analyzed using a profile fit. The decrease in the signal-to-noise ratio toward longer wavelengths is a result of declining detector sensitivity in this spectral regime and of decreasing sample quality as the synthesis and crystal growth is getting more complex for higher N-content. In addition to the recorded emission and excitation spectra, the thermal quenching behavior has been studied on a SrAl2−xLi2+xO2+2xN2−2x sample with x = 0.60. The temperature dependent loss in integral emission intensity is considerable as it drops by 60% if heated to 200 °C (see Supporting Information Figure S2). The internal quantum efficiency of SrAl2−xLi2+xO2+2xN2−2x has also been measured, resulting in a value of 75% for excitation at 500 nm and 65% for excitation at 450 nm (see next section). As the fwhm and thermal quenching are related to the Stokes shift, we estimated this value based on room temperature diffuse reflectance (DR) and emission spectra for the most pronounced electronic transitions (see Figure S3) to identify some basic trends (energy scale). Nevertheless, an in-depth analysis would require low temperature measurements of course. There is a correlation observable, meaning samples with high x value exhibit a large estimated Stokes shift and smaller fwhm values. The thermal quenching therefore could be affected by pronounced electron−phonon coupling. The minimum of the DR and maximum of the emission spectra shift in general to smaller energies for smaller x values. LED-Investigations. For the investigation of brightness, performance, and LED color point, prototype LEDs of the SrAl2−xLi2+xO2+2xN2−2x:Eu2+ (x ≈ 0.6) phosphor material were casted. As reference phosphor a commercially available αSiAlON phosphor was used.21−23 The resulting emission spectra are displayed in Figure 7 and illustrate that with SrAl2−xLi2+xO2+2xN2−2x:Eu2+ (x ≈ 0.6) orange LED solutions,

Figure 4. Diffuse reflectance spectrum (gray), excitation spectrum (blue), and emission spectrum (orange) of SrAl2−xLi2+xO2+2xN2−2x obtained from the same bulk sample with x = 0.44.

The emission maxima obtained from bulk samples with different compositions correlate well with the cell volume from the Rietveld refinement (see Figure 5). This goes to show that the emission maximum can be tuned continuously from 581 to 672 nm by a variation of the Al/Li and O/N stoichiometry. Emission spectra from the different bulk samples are displayed in Figure 6. The fwhm also changes due to the variation of the stoichiometry with the values ranging from 78.7 nm (2320 cm−1, 2.12 eV) for the emission peaking at 581 nm (x = 0.66)

Figure 5. Correlation between the cell volume of the samples with different x values and the emission wavelength from the corresponding luminescence measurements. D

DOI: 10.1021/acs.inorgchem.9b01479 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

barium contents up to 30%, the emission band blue-shifts resulting in emission maxima of up to 543 nm (see Supporting Information Figure S6). The structure has been refined from powder data via the Rietveld-method revealing the cell volume to be slightly larger than the one obtained from an unsubstituted sample with otherwise identical composition. Substitution experiments with calcium have also been carried out. There has been no sign of successful substitution, and to the best of our knowledge calcium was not incorporated into the structure.

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CONCLUSION SrAl2−xLi2+xO2+2xN2−2x:Eu2+ (0.12 ≤ x ≤ 0.66) could be synthesized via a solid state reaction and crystallizes isotypic to UCr4C4. Since this structural pattern is typical for nitride compounds, it is surprising that an oxonitride such as SrAl2−xLi2+xO2+2xN2−2x maintains this connectivity despite the lack of any apparent stabilizing effects. It can be described as a mixed occupancy variant of the recently published SALON phosphor and exhibits intense luminescence upon excitation with blue light. In comparison with SALON, the emission obtained from SrAl2−xLi2+xO2+2xN2−2x:Eu2+ is significantly broader. This can be explained by the variety of local environments for the Eu2+ activator ion resulting from the mixed occupancy on the oxygen/nitrogen site in SrAl2−xLi2+xO2+2xN2−2x:Eu2+ while the ordering observed in SALON leads to only one local environment and a therefore much narrower emission band. This difference in the structure may also be the reason for the slightly lower quantum efficiency and higher thermal quenching of SrAl2−xLi2+xO2+2xN2−2x:Eu2+ in comparison to the SALON phosphor, illustrating the importance of ordering phenomena for a phosphors performance. As there are only very few phosphors which tolerate high degrees of substitution on anionic sites, the effect of such a substitution on the luminescence is not yet clear. Substances such as SrAl2−xLi2+xO2+2xN2−2x:Eu2+ offer the opportunity to study such effects. The mixed occupancy in SrAl2−xLi2+xO2+2xN2−2x:Eu2+ also allows for a stoichiometry dependent shift of the emission maximum as the emission heavily depends on the exact stoichiometry of the sample. A continuous shift of the emission wavelength from 581 to 672 nm can be realized by varying the composition of the compound between x = 0.66 and x = 0.12. Additionally, a partial substitution with barium can be used to blue-shift the emission up to 543 nm.

Figure 7. Emission spectra of the SrAl2−xLi2+xO2+2xN2−2x:Eu2+ (x ≈ 0.6) enabled LED-solution and the α-SiAlON based reference.

comparable to those using α-SiAlON, can be realized. As can be seen in Figure 8, the SrAl2−xLi2+xO2+2xN2−2x phosphor is

Figure 8. CIE-diagram illustrating the color points of the SrAl2−xLi2+xO2+2xN2−2x:Eu2+ (x ≈ 0.6) enabled LED-solutions in comparison with the α-SiAlON based references.

able to meet CIE color points similar to that of the α-SiAlON phosphor. Both phosphors enable color points within the required color box for automotive indicator lights (ECE amber box). For the color point xCIE = 0.45, the performance level of SrAl2−xLi2+xO2+2xN2−2x is ∼60% of the commercial α-SiAlON, which makes the material an interesting candidate for further investigation and optimization (particle size, dopant concentration, purity, QE, stability, costs) to prove or disprove industrial application potential. Besides the application as automotive indicator, a usage in CRI70 white light mixtures could be considered.23 For further details of the corresponding color points, concentrations, the luminous flux, and the LER values, please refer to the Supporting Information (Table S4, Figure S4, and Figure S5). Barium Substitution. In addition to the variation of the Al/Li and O/N stoichiometry, the strontium can also be partially exchanged for barium. For these substitution experiments BaCO3 (Solvay) was used as an additional starting material while keeping the rest of the synthesis unchanged. This substitution, which has been carried out for formal

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b01479. Atom sites, Wyckoff positions, and displacement parameters, as well as data for the Rietveld refinement. A comparison of bulk and single crystal emission, the thermal quenching analysis, parameters and performance of the LED prototypes, and the emission spectra for the barium containing samples. (PDF) Accession Codes

CCDC 1912154 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing E

DOI: 10.1021/acs.inorgchem.9b01479 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

(14) Pust, P.; Wochnik, A. S.; Baumann, E.; Schmidt, P. J.; Wiechert, D.; Scheu, C.; Schnick, W. Ca[LiAl3N4]:Eu2+A Narrow-Band RedEmitting Nitridolithoaluminate. Chem. Mater. 2014, 26, 3544−3549. (15) Dutzler, D.; Seibald, M.; Baumann, D.; Huppertz, H. Alkali Lithosilicates Renaissance of a Reputable Substance Class with Surprising Luminescence Properties. Angew. Chem., Int. Ed. 2018, 57, 13676−13680. (16) Maak, C.; Eisenburger, L.; Wright, J. P.; Nentwig, M.; Schmidt, P. J.; Oeckler, O.; Schnick, W. RE4Ba2[Si12O2N16C3]:Eu2+ (RE = Lu, Y): Green-Yellow Emitting Oxonitridocarbidosilicates with a Highly Condensed Network Structure Unraveled through Synchrotron Microdiffraction. Inorg. Chem. 2018, 57, 13840 (17) Wilhelm, D.; Baumann, D.; Seibald, M.; Wurst, K.; Heymann, G.; Huppertz, H. Narrow-Band Red Emission in the Nitridolithoaluminate Sr4[LiAl11N14]:Eu2+. Chem. Mater. 2017, 29, 1204−1209. (18) Hoerder, G. J.; Seibald, M.; Baumann, D.; Schröder, T.; Peschke, S.; Schmid, P. C.; Tyborski, T.; Pust, P.; Stoll, I.; Bergler, M.; Patzig, C.; Reißaus, S.; Krause, M.; Berthold, L.; Höche, T.; Johrendt, D.; Huppertz, H. Sr[Li2Al2O2N2]:Eu2+A high performance red phosphor to brighten the future. Nat. Commun. 2019, 10, 1824. (19) Garcés, R. S.; Torres, J. T.; Valdés, A. F. Synthesis of SrAl2O4 and Sr3Al2O6 at high temperature, starting from mechanically activated SrCO3 and Al2O3 in blends of 3:1 molar ratio. Ceram. Int. 2012, 38, 889−894. (20) Fair, H. D.; Walker, R. F. Energetic Materials 1 - Physics and Chemistry of the Inorganic Azides; Springer: 1977. (21) van Krevel, J. W. H.; van Rutten, J. W. T.; Mandal, H.; Hintzen, H. T.; Metselaar, R. Luminescence Properties of Terbium-, Cerium-, or Europium-Doped α-Sialon Materials. J. Solid State Chem. 2002, 165, 19−24. (22) Xie, R.-J.; Hirosaki, N.; Mitomo, M.; Suehiro, T.; Xu, X.; Tanaka, H. Photoluminescence of Rare-Earth-Doped Ca-alphaSiAlON Phosphors: Composition and Concentration Dependence. J. Am. Ceram. Soc. 2005, 88, 2883−2888. (23) Yamada, S.; Emoto, H.; Ibukiyama, M.; Hirosaki, N. Properties of SiAlON powder phosphors for white LEDs. J. Eur. Ceram. Soc. 2012, 32, 1355−1358. (24) Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr. C 2015, 71, 3−8. (25) Shannon, R. D. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751−767. (26) Yamashita, N. Photoluminescence spectra of the Eu2+ center in SrO:Eu. J. Lumin. 1994, 59, 195−199. (27) Tsai, Y. T.; Nguyen, H. D.; Lazarowska, A.; Mahlik, S.; Grinberg, M.; Liu, R. S. Improvement of the Water Resistance of a Narrow-Band Red-Emitting SrLiAl3N4:Eu2+ Phosphor Synthesized under High Isostatic Pressure through Coating with an Organosilica Layer. Angew. Chem. 2016, 128, 9804−9808.

[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Hubert Huppertz: 0000-0002-2098-6087 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to thank Dr. Frank Jermann for initiating the cooperation between the University of Innsbruck and the OSRAM GmbH, Dr. Stefan Lange for advice and feedback regarding the possible application of the title compound, and Dr. Frauke Philipp for SEM-EDX measurements associated with this work.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.9b01479 Inorg. Chem. XXXX, XXX, XXX−XXX