Synthesis, Crystal Structure, and Photoluminescence of the Boron

Tohoku University, 2-1-1 Katahira, Aoba-ku , Sendai 980-8577 , Japan. Inorg. Chem. , Article ASAP. DOI: 10.1021/acs.inorgchem.8b00711. Publication...
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Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Synthesis, Crystal Structure, and Photoluminescence of the Boron− Aluminum−Silicon Nitride Phosphor Sr3BAl5Si9N20:Eu Fumitaka Yoshimura*,†,‡ and Hisanori Yamane‡ †

Mitsubishi Chemical Corporation. 1060 Naruda, Odawara City, Kanagawa 250-0862, Japan Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan

‡

S Supporting Information *

ABSTRACT: Single crystals of new boron−aluminum− silicon nitrides, Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20, were synthesized by heating binary nitride mixtures at 2030 °C under a N2 pressure of 0.85 MPa. The X-ray diffraction spots from single crystals of these two compounds were indexed with the trigonal cell parameters a = 22.7406(8) Å, c = 5.7066(2) Å and a = 22.7439(8) Å, c = 5.7050(2) Å, respectively, and the crystal structures were determined to have the space group P3c1, with B atoms situated at planar 3fold-coordinated N sites. A three-dimensional framework structure is constructed for these materials based on the sharing of N atoms of Al/Si−N4 tetrahedra and B−N3 triangles. In this framework, Sr/Eu atoms are located at three sites, surrounded by 10 N atoms. Single crystals of Sr2.91Eu0.09BAl5Si9N20 emitted yellow light with a peak wavelength of 565 nm and a full width at half-maximum of 106 nm under 450 nm light irradiation. The emission intensity of these crystals at 200 °C was found to be 12% of the intensity at 25 °C.

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INTRODUCTION Aluminum/silicon-based nitrides and oxynitrides have been investigated as host crystals for phosphors with applications in light-emitting diode lamps producing white light because of their promising luminescent properties, durability, and low thermal quenching at the operating temperature of the lamps.1−3 To expand the range of host crystal structures, various elements have been introduced into these nitrides and oxynitrides, and many new compounds have consequently been synthesized.4,5 Boron nitride (BN) is more and less stable than silicon nitride (Si3N4) and aluminum nitride (AlN), respectively [based on the formation free energies, ΔG: −228.4 kJ/ mol (BN), −287.0 kJ/mol (AlN), and −161.8 kJ/mol (1/ 4(Si3N4))]6,7 and is used as a material for crucibles. In the multinary nitrides containing B atoms reported in previous studies, the B atoms are present in isolated [BN2]3− groups or in [BN3]6− groups, both of which are surrounded by atoms of alkali, alkaline-earth, or rare-earth elements.8−11 Recently, Funahashi et al. synthesized single crystals having the formula Sr2−yEuyB2−2xSi2+3xAl2−xN8+x (x ≈ 0.12 and y ≈ 0.10) at 1800 °C and a N2 pressure of 1.0 MPa and analyzed the crystal structure.12 This compound is the first reported case of a threedimensional framework composed of B−N3 triangles and (Al/ Si)−N4 tetrahedra sharing N atoms. In this framework, the B− N3 triangles and (Al/Si)−N4 tetrahedra are statistically disordered. Broad emission spectra with peaks at 598 nm (x = 0.0) or 609 nm (x = 0.15) were observed for Sr1.99Eu0.01B2−2xSi2+3xAl2−xN8+x (y = 0.01) under 400 nm light irradiation.13 Retrofitting B−N3 triangles into the (Al/Si)−N4 © XXXX American Chemical Society

tetrahedral framework could result in new nitrides and phosphor materials with a wide range of structures. In our recent study, single crystals of a new B-containing nitride, Ba5B2Al4Si32N52:Eu, were prepared at 2050 °C and a N2 pressure of 0.85 MPa, and the crystal structure of this material was analyzed.14 This compound is the second example of a nitride having a structure in which B−N3 triangles are incorporated into an (Al/Si)−N4 framework. We also believe that this nitride represents the first case of a structure incorporating B−N3 triangles and (Al/Si)−N4 tetrahedra in a regular order, although stacking faults and reticular merohedral twins were observed via scanning transmission electron microscopy. The present paper reports the synthesis and crystal structure of a new B-containing nitride, Sr3BAl5Si9N20, and characterizes the luminescence properties of this compound following doping with europium. This nitride, having an ordered arrangement of B−N3 triangles and (Al/Si)− N4 tetrahedra based on shared apical N atoms, was crystallized without stacking faults.

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EXPERIMENTAL SECTION

Synthesis. Powders of strontium nitride (purchased as Sr3N2; 99.5% pure, 9.62% N, 0.26% O; Cerac Co.), EuN (99.9%, Cerac Co.), BN (99.5%, Mitsuwa Chemical Co., Ltd.), AlN (99%, Tokuyama Co.), and α-Si3N4 (>99%, Ube Industries, Ltd.) were used as the starting materials. The Sr3N2 powder was actually a mixture of Sr2N, SrN2, Received: March 16, 2018

A

DOI: 10.1021/acs.inorgchem.8b00711 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 1. Optical micrographs of Sr2.91Eu0.09BAl5Si9N20 single crystals under (a) white light and (b) 400 nm light irradiation. SrN, and SrH. Sr3N2 (154.5 mg), BN (13.2 mg), AlN (108.8 mg), and Si3N4 (223.5 mg; that is, the stoichiometric composition of Sr3BAl5Si9N20) were weighed for the sample 1 preparation, and Sr3N2 (148.9 mg), EuN (7.9 mg), BN (13.1 mg), AlN (108.1 mg), and Si3N4 (222.0 mg; that is, the composition of Sr2.91Eu0.09BAl5Si9N20) were weighed for the sample 2 preparation. The powders were mixed with an alumina mortar and pestle in a glovebox filled with Ar (Tokyo Koatsu Co. Ltd., > 99.9999%) and then transferred to a BN crucible with a lid (99.5%; inside diameter 18 mm; depth 18 mm; Showa Denko, K.K.). Each mixture was heated in a graphite resistance furnace (Shimadzu Mectem, Inc., VESTA) from room temperature to 800 °C under 8 × 10−3 Pa of N2 (99.9995%, Taiyo Nippon Sanso Corp.). From 800 to 2030 °C, the sample was heated under 0.85 MPa of N2 at 20 °C/min and then held at this temperature for 4 h. Each mixture was subsequently cooled to 1200 °C at 20 °C/min, after which the furnace was turned off and the sample was allowed to naturally cool to ambient temperature, maintaining a N2 pressure of 0.85 MPa. Characterization. Single crystals of approximately 100−700 μm size were separated from the resulting materials using a sieve having 72 μm openings and then embedded in metallic indium and coated with carbon. Elemental analysis of the single crystals was performed with an electron probe microanalyzer (Jeol JXA-8200). Depth profiles of B, Al, and Si atoms from the crystal surface were analyzed by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). Single-crystal X-ray diffraction (XRD) data were collected via the ω/φ scan method using a diffractometer employing Mo Kα radiation (Bruker, D8 QUEST). Data collection and unit-cell refinement were performed with the APEX3 software package,15 and a multiscan absorption correction was applied using the SADABS program.16 An initial structural model was generated by a direct method using the SIR2004 program,17 while the structural parameters of the crystals were refined by employing the SHELXL-97 program,18 and the crystal structures were drawn with the VESTA program.19 The crystalline phases in the products were identified by powder XRD using Cu Kα radiation (Bruker, D2 PHASER). Photoluminescence (PL) excitation and emission spectra were acquired from single-crystal grains set in a copper holder with a quartz-glass window over the range of 25−300 °C using a fluorescence spectrophotometer (FP-6500, JASCO) equipped with a 150 W xenon lamp.

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the synthesis process, suggesting that some of the Sr−N component evaporated during the firing. The main phase of sample 2 was composed of yellow prismatic crystals of Sr2.91Eu0.09BAl5Si9N20, with lengths of approximately 0.7 mm, as can be seen in the optical micrograph in Figure 1a. These crystals generated a yellow emission under 400 nm light irradiation (Figure 1b). The secondary phases were platelets of orange SrAlSi4N7:Eu2+ single crystals, as was also reported by Hecht et al.,20 and a white powder composed of an unidentified phase and BN. The Sr:Al:Si and Sr:Eu:Al:Si atomic ratios in the Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20 crystals as determined b y e le c t r o n p r o be m i c r o a n a ly si s (E P M A) w e r e 3.00(1):5.06(1):9.13(4) and 2.85(6):0.15(1):4.96(3):8.94(4), respectively. These values are consistent with the elemental ratios of the formulas. N was detected, but neither B nor O was detected by EPMA, although 2.6 atom % B was expected to be present in both compounds. However, uniform distributions of B as well as Al and Si in a single crystal of Sr2.91Eu0.09BAl5Si9N20 from sample 2 were identified in the TOF-SIMS elemental depth profiles (Figure S1). The XRD reflections from the Sr 3 BAl 5 Si 9 N 20 and Sr2.91Eu0.09BAl5Si9N20 crystals were indexed with the trigonal cell parameters a = 22.7406(8) Å, c = 5.7066(2) Å and a = 22.7439(8) Å, c = 5.7050(2) Å, respectively. No streak lines indicating stacking faults of the structure were observed in the reciprocal lattice planes reconstructed from the single-crystal data for Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20. The systematic absence of reflections indicated either the P3c1 or P3 c1̅ space group, and the initial structural model was obtained using the P3c1 space group by a direct method. Three Sr or Sr/Eu sites were identified, along with one B site, 14 Al/Si sites, and 22 sites for N atoms. The Al and Si occupancies at the Al/Si sites were refined while constraining the total Al:Si ratio to a value of 5:9, with no deficiencies. TWIN and BASF instructions with a matrix (0 1 0, 1 0 0, 0 0 1) were applied in the structure refinement. The data collection conditions and refinement results with R1 (all data) values of 1.32% and 1.57% for the analyses of Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20, respectively, are summarized in Table 1. The atomic coordinates, equivalent isotropic atomic displacement parameters, and the anisotropic displacement parameters are listed in Tables S1−3, while the interatomic distances in Sr 3 BAl 5 Si 9 N 20 and Sr2.91Eu0.09BAl5Si9N20 are given in Table S4. In the structural analysis of Sr2.91Eu0.09BAl5Si9N20, the Eu occupancies at the Sr/Eu1, Sr/Eu2, and Sr/Eu3 sites were refined to give values of 0.024(3), 0.022(3), and 0.029(3),

RESULTS AND DISCUSSION

Synthesis and Crystal Structure of Single Crystals. Sample 1 consisted of colorless, transparent rodlike single crystals of the new compound Sr3BAl5Si9N20 as the main phase, with a size of approximately 500 μm. A secondary phase was also identified, composed of platelike transparent single crystals of SrAlSi4N7 with widths of approximately 30 μm, in keeping with an earlier report by Hecht et al.,20 as well as a fine white powder consisting of a mixture of BN and an unidentified compound. This sample exhibited a mass loss of 4.6% during B

DOI: 10.1021/acs.inorgchem.8b00711 Inorg. Chem. XXXX, XXX, XXX−XXX

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six shorter values ranging from 2.621(3) to 2.799(4) Å and four longer distances from 3.228(4) to 3.436(4) Å. Figure 2 shows the arrangement of N atoms around the Sr1− 3 sites. Here, the Sr1-, Sr2-, and Sr3-centered 10-fold-

Table 1. Crystal Data and Refinement Results for Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20 chemical formula fw, Mr (g mol−1), Z cryst form, color cryst size (mm3) radiation wavelength, λ (Å) temperature, T (K) cryst syst, space group unit-cell dimens a = b (Å) c (Å) α = β (deg), γ (deg) unit-cell volume, V (Å3) calcd density, Dcal (Mg m−3) abs coeff, μ (mm−1) abs corrn limiting indices θ range for data collection (deg) reflns collected/ unique Rint date/restraints/ param wt param, a, b GOF on F2, S R1, wR2 [I > 2σ(I)]a R1, wR2 (all data)a largest diff peak and hole (e Å−3)

Sr3BAl5Si9N20 941.58, 6 prismatic, colorless 0.095 × 0.103 × 0.189 0.71073

Sr2.91Eu0.09BAl5Si9N20 947.37, 6 prismatic, yellow 0.046 × 0.053 × 0.184 0.71073

301(2) trigonal, P3c1 (No. 158)

301(2) trigonal, P3c1 (No. 158)

22.7406(8) 5.7066(2) 90, 120

22.7439(8) 5.7050(2) 90, 120

2555.7(2)

2555.7(2)

3.671

3.693

10.314 multiscan (SADABS16) −32 ≤ h ≤ 32, −32 ≤ k ≤ 32, −7 ≤ l ≤ 6 1.79−30.55

10.361 multiscan (SADABS16) −32 ≤ h ≤ 32, −32 ≤ k ≤ 32, −8 ≤ l ≤ 8 1.79−30.52

103767/5198

104289/5190

0.0416 5198/2/358

0.0491 5190/2/361

0.0146, 0 1.017 0.0129, 0.0311

0.0167, 0 1.031 0.0151, 0.0351

0.0131, 0.0312 0.375 and −0.333

0.0157, 0.0353 0.380 and −0.339

Figure 2. N-atom arrangement around the Sr atoms in the crystal structure of Sr3BAl5Si9N20, illustrated using Sr-centered N polyhedra (Sr−N10). Displacement ellipsoids are drawn at the 99% probability level.

coordinated N polyhedra all have almost the same volumes of 46.89, 46.56, and 46.93 Å3, respectively. In addition, the bond-valence sums of the Sr1, Sr2, and Sr3 sites as calculated using the bond-valence parameter R0(Sr−N) = 2.23 Å21 were found to be 1.93, 1.93, and 1.97, respectively, all of which are close to the formal valence of SrII. Figure 3 presents the crystal structure of Sr3BAl5Si9N20 based on 10-fold-coordinated N polyhedra, projected from the c-axis

R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = [∑w(Fo2 − Fc2)2/∑(wFo2)2 ]1/2, w = 1/[σ2 (Fo2) + (aP)2 + bP], where Fo is the observed structure factor, Fc is the calculated structure factor, σ is the standard deviation of Fc2, and P = (Fo2 + 2Fc2)/3. S = [∑w(Fo2 − Fc2)2/(n − p)]1/2, where n is the number of reflections and p is the total number of parameters refined. a

respectively (Table S1). The Sr:Eu ratio of 2.91:0.09 in the formula Sr2.91Eu0.09BAl5Si9N20 derived from the occupancy refinement was in accordance with the composition of the starting material and the results of EPMA. As shown in Table 1, Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20 have the same unit-cell volume. As well, the interatomic distances between the Eu/Sr and N sites in Sr2.91Eu0.09BAl5Si9N20 are in agreement with those between the Sr and N sites in Sr3BAl5Si9N20 within the standard deviations. These similarities may be associated with the similar sizes of the Sr and Eu atoms in the structure, indicated by the small differences between the bond-valence parameters R0(Sr−N) = 2.23 Å and R0(Eu−N) = 2.24 Å.21 The interatomic distances between the Sr and N atoms at each Sr site are plotted in ascending order in Figure S2, from which it is evident that gaps are present between the 10th and 11th lengths for all Sr sites. The distances of the Sr1−N and Sr3−N sites increase monotonically from 2.675(3) to 3.295(2) Å and from 2.621(3) to 3.118(3) Å, respectively (Table S4). In contrast, the distances of the Sr2−N sites can be grouped into

Figure 3. Crystal structure of Sr3BAl5Si9N20 illustrated using B1centered N triangles (B−N3) and Sr-centered N polyhedra (Sr−N10).

direction. Two pairs of Sr1−N10, Sr2−N10, and Sr3−N10 polyhedra are aligned around the 3-fold (0, 0, z), (1/3, 2/3, z), and (2/3, 1/3, z) axes, respectively, and the Sr1−N10, Sr2− N10, and Sr3−N10 polyhedra are linked by sharing N14 sites, as shown in Figure 2. The arrangements of N atoms around the B1 and Al/Si1−14 sites of Sr3BAl5Si9N20 are shown in Figure 4. In this structure, the bond angles ∠N1−B1−N5 = 117.8(3)°, ∠N12−B1−N1 = 118.6(3)°, and ∠N5−B1−N12 = 123.2(3)° indicate the 3-fold planar coordination of the N atoms. The interatomic distances between the B and N atoms in Sr 3 BAl 5 Si 9 N 20 and Sr2.91Eu0.09BAl5Si9N20 were determined to be equal within the standard deviations (Table S4). The B−N bond lengths in the B−N3 triangles range from 1.443(4) to 1.479(4) Å, which is consistent with the values previously reported for C

DOI: 10.1021/acs.inorgchem.8b00711 Inorg. Chem. XXXX, XXX, XXX−XXX

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in Figure 5. The linear fitting of the average Al/Si−N distances for Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20 is situated approximately 0.02 Å above the line for the Si−N and Al−N lengths, as obtained from the ionic radii, although the slopes of both lines are almost the same. The bond-valence sums of the Al/Si sites calculated using the bond-valence parameter R0(Si−N) = 1.77 Å21 (Table S4) also tended to decrease with increasing Al occupancies (Figure S3). A three-dimensional framework structure was constructed by sharing N atoms of (Al,Si)−N4 tetrahedra and B−N3 triangles (Figures 3 and 4), and the atomic arrangement around the N atoms is shown in Figure 6. Each N atom is bonded to three

Figure 4. N-atom arrangement around Si/Al atoms in Sr3BAl5Si9N20. The occupancies of the Al and Si atoms in the Al/Si spheres are indicated by aqua and blue, respectively.

Sr2−yEuyB2−2xSi2+3xAl2−xN8+x [1.4874(14) Å]12 and for isolated [BN3]6− groups [1.471(6) Å].8 The bond-valence sum for B1, as calculated using a B−N bond-valence parameter of 1.47 Å,21 was 3.07, which is in agreement with a B valence of three (Table S4). The occupancies of the Al and Si atoms at the Al/Si sites are indicated by the shaded areas in the spheres in Figure 4. Because the X-ray scattering powers of the Al and Si atoms are close, it is often difficult to refine the occupancies of the Al and Si atoms that statistically occupy the same sites. However, the occupation factors of the Al and Si atoms for all Al/Si sites could be refined to some extent in the present structural analyses of Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20, with a deviation of approximately 0.05. Figure 5 plots the relationship

Figure 6. Al/Si- and Sr-atom arrangements around the N atoms in Sr3BAl5Si9N20. Displacement ellipsoids are drawn at the 99% probability level.

Al/Si atoms or two Al/Si and B atoms except for the N atom at the N14 site, which is connected to two Al/Si atoms at the Al/ Si8 and Al/Si11 sites and surrounded by three Sr atoms at the Sr1, Sr2, and Sr3 sites. Two Sr atoms are located near N atoms at the N1, N2, N5, N8, N10, N12, N13, N16, and N18 sites, while one Sr atom is near the N atoms at the N3, N4, N6, N7, N9, N15, N17, and N19 sites, within a N−Sr distance of 3.5 Å. No Sr atoms are situated near the N11, N20, N21, and N22 sites. In the case of boroaluminosilicates, various structures can be constructed from combinations of (Al/Si)−O4 tetrahedra, B− O3 planar triangles, and B−O4 tetrahedra.23−25 In these structures, O2− anions are bonded to one or two Al/Si and/ or B atoms. However, in nitridoaluminosilicates, the N atoms can bound to three Al/Si atoms, realizing unique threedimensional frameworks that are not found in oxides.4 The crystal structure of Sr3BAl5Si9N20 is likely a new type that does not yet appear in the Inorganic Crystal Structure Database (ICSD). As in the case of oxoboroaluminosilicates, it is expected that additional new nitrides will be synthesized by combining (Al/Si)−N4 tetrahedra and B−N3 planar triangles in future studies. Luminescence Properties of Sr2.91Eu0.09BAl5Si9N20 Single Crystals. PL excitation and emission spectra were acquired from Sr2.91Eu0.09BAl5Si9N20 single crystals (grain size, 100−700 μm), and Figure 7 shows the excitation wavelength

Figure 5. Al/Si−N distances as functions of the Al occupancies in the Al/Si sites of Sr3BAl5Si9N20 (○) and Sr2.91Eu0.09BAl5Si9N20 (△).

between the average Al/Si−N interatomic distance and the Al occupancy for each site. The average Al−N distances for the same sites in Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20 were comparable, and these distances tended to increase with increasing Al occupancy. The Al−N (1.85 Å) and Si−N (1.73 Å) distances calculated using the ionic radii of IVAl3+ (0.41 Å), IV 4+ Si (0.29 Å), and IIIN3− (1.44 Å) by Baur22 are also included D

DOI: 10.1021/acs.inorgchem.8b00711 Inorg. Chem. XXXX, XXX, XXX−XXX

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583 nm and between 47.3 and 43.3 Å3 reported for βSrAlSi4N7:Eu34 and Sr0.31Al0.62Si11.38N16:Eu,32 respectively, while the coordination numbers of all Sr sites in the structures of these nitrides are 10. The combination of the B−N3 triangles and (Al,Si)−N4 tetrahedra in the framework of Eu2+-doped Sr3BAl5Si9N20 may have realized N coordination environments around the Sr/Eu2+ atoms, with the volumes of the N polyhedra appropriate for the yellow emission with the unique wavelength. The temperature dependence of the relative emission intensity of Sr2.91Eu0.09BAl5Si9N 20 under 450 nm light irradiation is shown in Figure 9, in which the emission intensity

Figure 7. Excitation and emission spectra acquired from Sr2.91Eu0.09BAl5Si9N20 single crystals at 25 °C.

dependence of the emission intensity at 565 nm and the emission spectra in response to irradiation at 450 nm. Luminescence was observed beginning at approximately 480 nm, and the peak wavelength (λem) and full width at halfmaximum (fwhm) of the emission spectrum were 565 and 106 nm, respectively, with a tail stretching out to approximately 750 nm. The peak position of the excitation spectra was 350 nm, after which the intensity was gradually decreased up to 480 nm. The ranges and averages of the Sr−N distances and the volumes of Sr-centered N polyhedra for Sr3BAl5Si9N20 and previously reported strontium silicon nitrides (SrSiN2, Sr2Si5N8, and SrSi6N8) and strontium aluminum silicon nitrides (Sr0.31Al0.62Si11.38N16, SrAlSiN3, α-SrAlSi4N7, β-SrAlSi4N7, and Sr3Al6Si24N40), as well as emission peak wavelengths for 1−3% Eu2+-doped ones,26−34 are summarized in Table S5. The volumes of the N polyhedra were calculated based on the reported coordination numbers. The coordination numbers of Sr1, Sr2, and Sr3 sites for Sr3Al6Si24N40, which were not presented in the literature,32 were determined to be 8, 9, and 11, respectively, by the plots of the Sr−N distances (Figure S4). As shown in Figure 8, the emission peak wavelengths decrease with increasing volume and Sr-site-number-weighted average volumes of the N polyhedra, which is consistent with the emission wavelength shift explained by the crystal-field theory.35 The wavelength (565 nm) and average volume of N polyhedra (46.8 Å3) for Sr3BAl5Si9N20 are between 541 and

Figure 9. Temperature dependence of the emission intensities for Sr2.91Eu0.09BAl5Si9N20 under 450 nm light irradiation (yellow solid circle) and for Ba5B2Al4Si32N52:Eu under 330 nm light irradiation (teal solid square).

at each temperature has been normalized to that at 25 °C. The emission spectra obtained at high temperatures are provided in Figure S5. Although the peak wavelength at 565 nm was almost unchanged when the temperature was increased from 25 to 300 °C, the relative emission intensity was rapidly decreased to 19% at 160 °C and to 3% at 300 °C. The B-containing nitrides Sr1.99Eu0.01B2−2xAl2−xSi2+3xN8+x13 and Ba5B2Al4Si32N52:Eu14 reported in previous studies also showed rapid decreases in their relative emission intensities with increasing temperature. Further studies are required to determine if this pronounced temperature quenching is common to nitrides having a framework structure composed of B−N3 triangles and (Al/Si)−N4 tetrahedra.

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CONCLUSIONS

Single crystals of Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20 were obtained by heating binary nitride starting mixtures in a BN crucible at 2030 °C and a N2 pressure of 0.85 MPa. TOF-SIMS analysis confirmed that B was uniformly distributed throughout these materials. These B atoms were coordinated with three N atoms in a planar manner and incorporated into a threedimensional Al/Si−N4 tetrahedra network via the sharing of vertex N atoms in the Sr3BAl5Si9N20 crystal structure. The Sr/ Eu atoms in the framework were coordinated with 10 N atoms. The peak wavelength and fwhm in the emission spectrum acquired from single crystals of Sr2.91Eu0.09BAl5Si9N20 were 565 and 106 nm, respectively, under 450 nm light excitation at 25 °C. At 200 °C, the emission intensity of Sr2.91Eu0.09BAl5Si9N20 crystals was found to decrease to 12% of the value at 25 °C.

Figure 8. Emission peak wavelengths of Eu2+-doped Sr3BAl5Si9N20 and Sr−Al−Si nitrides versus the volumes and average volumes of Srcentered N polyhedra. E

DOI: 10.1021/acs.inorgchem.8b00711 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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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.8b00711. Tables of atomic coordinates, equivalent isotropic and anisotropic displacement parameters, interatomic distances, and N polyhedron volumes for Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20 and N polyhedral volumes for Sr3BAl5Si9N20 and strontium−aluminum−silicon nitrides and the emission peak wavelengths of the Eu2+-doped ones and figures of the TOF-SIMS depth profile for Sr2.91Eu0.09BAl5Si9N20, Sr−N distances and bond valence sums versus Al occupancies for the Al/Si sites of Sr3BAl5Si9N20 and Sr2.91Eu0.09BAl5Si9N20, Sr−N distances for Sr2.97Eu0.03Al6Si24N40, and emission spectra of Sr2.91Eu0.09BAl5Si9N20 at 25−300 °C (PDF) Accession Codes

CCDC 1831612−1831613 contain 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 [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

*Phone/Fax: +81 465 35 1140/6887. E-mail: yoshimura. [email protected] (F.Y.). ORCID

Fumitaka Yoshimura: 0000-0002-0548-7167 Hisanori Yamane: 0000-0002-7931-5210 Notes

The authors declare the following competing financial interest(s): This work was supported by Mitsubishi Chemical Group, Science and Technology Research Center, Inc. (a joint research of Tohoku University and Mitsubishi Chemical Group, Science and Technology Research Center, Inc., J140000549).

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ACKNOWLEDGMENTS The authors thank Eiko Kobayashi, Yuko Suzuki, Ayumi Honda, and Yumi Oikawa for their assistance with the sample preparation and characterization of the luminescence properties, as well as Takashi Kamaya for EPMA and Rie Shishido for TOF-SIMS analysis.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.8b00711 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.8b00711 Inorg. Chem. XXXX, XXX, XXX−XXX