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Article

Novel “Anti-Zeolite” Ba3Sr3B4O12: Eu3+ Phosphors: Crystal Structure, Optical Properties, and Photoluminescence

by
Rimma S. Bubnova
1,*,
Andrey P. Shablinskii
1,
Alexey V. Povolotskiy
2,
Olga Yu. Shorets
1,
Valery L. Ugolkov
1,
Sergey N. Volkov
1,3,
Valentina A. Yukhno
1 and
Stanislav K. Filatov
4
1
Institute of Silicate Chemistry of the Russian Academy of Sciences (ISC RAS), Makarova Emb. 2, Saint Petersburg 199034, Russia
2
Institute of Chemistry, St. Petersburg State University, Universitetskaya Emb. 7/9, Saint Petersburg 199034, Russia
3
Laboratory of Arctic Mineralogy and Material Sciences, Kola Science Centre, Russian Academy of Sciences, Fersmana St. 14, Apatity 184209, Russia
4
Institute of Earth Sciences, St. Petersburg State University, Universitetskaya Emb. 7/9, Saint Petersburg 199034, Russia
*
Author to whom correspondence should be addressed.
Symmetry 2023, 15(7), 1399; https://doi.org/10.3390/sym15071399
Submission received: 16 June 2023 / Revised: 1 July 2023 / Accepted: 7 July 2023 / Published: 11 July 2023
(This article belongs to the Special Issue Symmetry in Inorganic Crystallography and Mineralogy)
Browse Figures
Versions Notes

Abstract

:
Novel Ba3Sr3B4O12: Eu3+ phosphors were synthesized by crystallization from a melt. The crystal structures of Ba3(Sr3−1.5xEux)B4O12 (x = 0.03, 0.06, 0.15, 0.20, 0.25) solid solutions were refined from SCXRD data. The crystal structures of Ba3(Sr3−1.5xEux)B4O12 phosphors can be described in terms of the cationic sublattice and belong to the “anti-zeolite” family of borates. Its cationic framework is constructed of Ba and Sr atoms. The Eu3+ ions occupy the Sr(1) extraframework cationic site in the Ba3(Sr3−1.5xEux)B4O12 (x = 0.01–0.20) phosphors. The Ba3Sr2.625Eu0.25B4O12 borate crystallizes in a new structure type (I4/mcm, a = 13.132(3), c = 14.633(4) Å, V = 2523.5(11) Å3, Z = 8, R1 = 0.067). In the Ba3Sr2.625Eu0.25B4O12 crystal structure, the Eu3+ ions occupy Sr(1) and Ba/Sr(1) sites, which leads to changes in the crystal structure. The Wyckoff letter and occupancy of the O(5) site are changed; B–O anion groups contain two BO3 triangles (B(3) and B(4)), orientationally disordered over the four orientations, and two ordered BO3 triangles (B(1) and B(2)) in contrast to Ba3Sr3B4O12, in which these groups are disordered over the 4 and 8 orientations. The emission spectra of Ba3Sr3B4O12: Eu3+ show characteristic lines corresponding to the intraconfigurational 4f-4f transitions of Eu3+ ions. Ba3Sr2.7Eu0.20B4O12 demonstrates the strongest luminescent intensity among Ba3(Sr3−1.5xEux)B4O12 solid solutions. The increase in the Eu3+ content results in a gradual change in chromaticity from light red to orange-red/red. It can be concluded that Ba3Sr3B4O12: Eu3+ is a promising red phosphor.

1. Introduction

A combination of rich crystal chemistry [1,2,3,4,5,6] and excellent optical properties makes borates important prospective materials [7,8]. Alkaline earth and rare-earth borates also attract great interest as NLO and luminescent materials for different applications [9,10,11]. The investigations of new borate matrices, which include rare-earth ions, make it possible to create new phosphors and laser materials due to isomorphic substitution. The rare-earth ions most often replace the alkaline earth atoms that are close in ionic radius and coordination number. Recently, it was shown that Eu3+-containing matrices have some advantages, especially for crystal structures with a few independent sites for alkaline earth and rare-earth metals [12,13,14,15,16,17,18,19].
This work is aimed at searching for new matrices for red-emitting phosphors in the SrO–BaO–B2O3 system. In the phase relations study of the BaB2O4–SrO section of the ternary system, a compound with the preliminary formula Ba5Sr6B10O26 was discovered, but its diffraction pattern was not indexed [20]. Limited Ba1−xSrxB2O4 solid solutions in a eutectic system based on SrB2O4 and BaB2O4 compounds were investigated [20]. The crystal structure of Ba1−xSrxB2O4 with x = 1.16 was refined in [21]; it turned out to be similar to α-BaB2O4. The Ba0.87Sr3.13B14O25 solid solution was refined in [22]. Later, the Ba2Sr3B4O11 crystal structure was resolved instead of Ba5Sr6B10O26 [23], and the Ba2Sr3B4O11 borate is structurally similar to Ba5B4O11 borates [24]. In 2018, the crystal structure of Ba3(BO3)2 was resolved in a novel structure type that can be described as “anti-zeolite” with the structural formula [Ba12(BO3)6](BO3)2 [25]. Finally, the disordered Ba3Sr3B4O12 borate was obtained for the first time and its crystal structure was similar to the “anti-zeolite” structural family [23]. The Ba3Sr3B4O12 crystal structure (I4/mcm, a = 13.102(3), c = 14.644(4) Å, V = 2514 (1) Å3) consists of isolated BO3 radicals oriented in a non-parallel manner. It contains BO3 triangles orientationally disordered over the 4 and 8 orientations.
The “Anti-zeolite” borate family contains many compounds which crystallize in different space groups; Ba6B4O12 [25], Ba12(BO3)6(BO3)2−2x[F2]x[F4]x [26], Ba12(BO3)6(BO3)2−2x[F2]x[F4]x:Cu [27] were described in Pbam, while Ba12(BO3)6(BO3)[LiF4] and Ba12(BO3)6(BO3)[NaF4] [28] were described in the P42bc space group. Ba12(BO3)6(BO3)2−2x[MnF6]x [29] and NdxBa12(BO3)8−xF6x [30] belong to the I4/mcm space group.
In this study, the novel red-emitting Ba3Sr3B4O12: Eu3+ phosphor was synthesized by cooling from a melt. There are three independent sites in Ba3Sr3B4O12 borate for Ba and Sr cations, in which Ba and Sr atoms are partially ordered [23]: Sr(1), Ba(1), and Sr/Ba(1). A comparison of the cations Ir and the average bond lengths of the Ba(1)O8, Sr(1)O7, and Sr/Ba(1)O11 gave us the expectation that Sr(1) is the preferable crystallographic site for Eu3+ incorporation. The crystal structure of Ba3(Sr3−1.5xEux)B4O12 (x = 0.03, 0.06, 0.15, 0.20, 0.25) solid solutions and distribution of the Eu3+ ions over cation sites were refined, and luminescent and optical properties were investigated.

2. Materials and Methods

The Ba3(Sr3−1.5xEux)B4O12 (x = 0.01, 0.03, 0.06, 0.15, 0.20, 0.25) phosphors were synthesized by mixing BaCO3 (Reahim, 99.99% purity), H3BO3 (Neva Reaktiv, 99.90% purity), SrCO3 (Reahim, 99.99% purity), and Eu2O3 (Kyrgyz CMC, 99.93% purity) in their stoichiometric ratios. The pellets of the reactant mixtures were heated in platinum crucibles at 900 °C for 20 h and at 1000 °C for 12 h. After that, the samples were melted at 1400 °C and cooled to room temperature over 7 h.
The samples were characterized by powder X-ray diffraction using a Rigaku Smart SE diffractometer (CuKα, 2θ = 3–120°, step 0.02). The phase composition was determined using the PDF-2 (ICDD) database. X-ray phase analysis revealed that the polycrystalline samples of Ba3(Sr3−1.5xEux)B4O12 (x = 0.01, 0.03, 0.06, 0.12, 0.15, 0.20, 0.25) were homogenous.
Single crystals of Ba3(Sr3−1.5xEux)B4O12 (x = 0.03, 0.06, 0.15, 0.20, 0.25) phosphors were selected using an optical microscope in polarized light from polycrystalline aggregates and then attached to the end of glass fiber using an epoxy glue. The experimental data were collected on a Rigaku XtaLab Synergy-S diffractometer equipped with high-speed direct-action detector HyPix-6000HE. A hemisphere of three-dimensional data was collected using MoKα radiation and frame width of 1° in ω, with 25 s used to acquire each frame. The data were interpolated into the CrysAlisPro software (2015) for further processing. An absorption correction was introduced using the SCALE3 ABSPACK algorithm. The crystal structures were refined with the JANA2006 program package [31]. The main details of the X-ray diffraction experiment and selected bond lengths are summarized in Table 1 and Table 2. Final atomic coordinates and displacement parameters are given in Tables S1–S10. Occupancies of the cation sites were refined from the experimental site-scattering factors in accordance with the chemical composition (Table S11). Strontium scattering curves were used to refine site occupancy. The criteria for occupancy assignment are scattering power, coordination number, and average bond lengths. Further details of the crystal structure investigations can be obtained from the Cambridge Structural Database on quoting the depository numbers CSD 2269856, 2269867, 2269885, 2269886, and 2269887.
The absorption spectra were measured with a Lambda 1050 (Perkin Elmer) spectrometer. To avoid the influence of light scattering, measurements were carried out in the 150 mm integrating sphere. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra and emission kinetic curves were measured on a Fluorolog-3 spectrometer (Horiba Jobin Yvon, Darmstadt, Germany). To study the luminescent properties, polycrystalline powders were pressed into KBr tablets. The vibrational spectra were obtained with a LabRam HR800 spectrometer (Horiba Jobin Yvon).
The DSC studies of Ba3(Sr3−1.5xEux)B4O12 (x = 0.03, 0.15, 0.25) solid solutions were performed on NETZSCH STA 429 with the use of a standard sample holder for measuring the differential scanning calorimetry (DSC)/differential thermal analysis (DTA) and thermogravimetry (TG) curves. The samples in the form of tablets were placed in a platinum crucible and heated up to 1500 °C in air at a rate of 20 °C/min. The sample weight was about 30 mg. The temperatures of the thermal effects were estimated as onset temperatures. According to the TG data, very small mass losses gradually occurred during heating, apparently due to the high heating rate.

3. Results and Discussion

3.1. Powder X-ray Diffraction of the Ba3(Sr3−1.5xEux)B4O12 (x = 0.01, 0.03, 0.06, 0.12, 0.15, 0.20, 0.25) Phosphors

Powder XRD patterns for all studied samples are shown in Figure 1. The samples are homogeneous and peaks correspond to the calculated XRD patterns of Ba3(Sr3−1.5xEux)B4O12 borates in accordance with data [23]. Unit cell parameters were refined by the Rietveld method in the RTT program software (v.2). The a parameter is decreased with the increase in Eu content as well as the volume V of the Ba3(Sr3−1.5xEux)B4O12 phosphors, due to the difference in the ionic radii of the Sr ([7]1.35 Å) and Eu ([7]1.15 Å) ions [32] (Figure 2), while the c parameter is increased slightly to about x = 0.10–0.15 Eu3+, but practically does not increase further. It could be assumed that the inflection point may be caused by a partial redistribution of Eu ions over Sr(1) and Sr/Ba(1) sites, as occurred in Ba3Lu2B6O15 [19].

3.2. Thermal Analysis

DSC curve of the x = 0.03 solid solution demonstrates small thermal effects on heating at 1194 and 1262 °C and a strong effect at 1305 °C (Figure 3a). The thermal effects at 1194 and 1305 °C refer to solidus and liquidus temperatures; these effects agree with data for Ba3Sr3B4O12 (1188 and 1343 °C) from [23]. The temperature of the strong effect is lower due to lowering of the liquidus temperature for solid solutions. The intermediate small thermal effect at 1262 °C may be caused by the recrystallization of solid solutions during their melting. The melting process of solid solutions occurs via the two-phase (solid and liquid) region, in which the chemical compositions of liquid and solid phases are continuously changed from solidus to liquidus temperatures. The Ba3B2O6 compound melts congruently at 1390 °C [25]. Therefore, the solidus and liquidus temperatures for disordered Ba3Sr3B4O12 and Ba3(Sr2.965Eu0.03)B4O12 solid solutions are significantly lower relative to Ba3B2O6.
DSC heating curves of x = 0.15 and x = 0.25 samples are very similar (Figure 3b,c), although they differ from the curve with x = 0.03. They demonstrate broadened overlapping peaks of solid solutions melting (Figure 3b,c). The thermal effects start at 1224 and 1226 °C for x = 0.15 and x = 0.25 samples, respectively. Apparently, these peaks (maxima at 1267 and 1264 °C) correspond to solidus temperatures, while the final maxima (1329 and 1331 °C) are liquidus temperatures. Intermediate insignificant peaks are attributed as recrystallization due to reaction of the solid phase and liquid with chemical composition changes for solid and liquid phases. The melting region of solid solutions with a high Eu3+ content (x = 0.15 and 0.25) is narrower than in the case of x = 0.03, which can apparently indicate a change in the structure of the solid solutions.

3.3. Crystal Structure Description

There is one symmetrically independent Ba, one Sr, one Sr/Ba, four B, and six O sites in crystal structures of Ba3(Sr3−1.5xEux)B4O12 solid solutions. The Ba(1), Sr(1), and Sr/Ba(1) are surrounded by six/eight, seven, and eleven oxygen atoms, respectively.
The crystal structures of Ba3(Sr3−1.5xEux)B4O12 phosphors, borates with isolated B–O anions, can be described in terms of the cationic sublattice and belong to the “antizeolite” family of borates [25,28,29,33,34]. This structure is formed by a tetragonal cationic framework of Ba and Sr atoms with square, pentagonal, and triangular cavities (Figure 4, bottom) filled by B–O anionic groups, as in Ba3B2O6 borate [25]. Each square cavity is surrounded by four pentagonal and triangular ones. This framework can be divided into A and B double pseudolayers [34] due to inversion center and mirror plane along the c axis (Figure 4, center). The [B(1)O3] and [B(2)O3] triangular radicals are located in pentagonal and triangular cavities inside A pseudolayers. The Sr(1) is an extraframework cationic site which is located within B pseudolayers.
The large channels in the Ba3(Sr2.70Eu0.20)B4O12 crystal structure are formed by square cavities of cationic nets: face-to-face connected “cubes” and anti-cubes (Figure 5, left center) forming a system of channels along the c axis. There are [B(3)O3] and [B(4)O3] groups in these channels. They are disordered over the 4 and 8 orientations, in contrast to Ba3B2O6, in which these groups are disordered over the 4 orientations.
In the Ba3(Sr3−1.5xEux)B4O12 (x = 0.03–0.20) crystal structures, the Eu3+ atoms occupy the Sr(1) extraframework cationic site according to single-crystal X-ray diffraction data. Preferably, Eu3+ ions may replace Sr ions, since the ions have similar ionic radii Rcryst ([7]Sr = 1.35 and [7]Eu3+ = 1.15 Å), in contrast to barium ([7]Ba = 1.52 Å). If the Sr(1) site is occupied by Eu3+ ions by more than 20%, then, as the concentration increases, the Eu3+ ions begin to occupy the Sr/Ba(1) site. Previously, the solid solutions of the “anti-zeolite” family were obtained by substitution of the disordered BO3 groups in the square cavity by different anionic groups [26,27,28,29,30]. Therefore, the Ba3(Sr3−1.5xEux)B4O12 solid solutions are the first examples of extraframework cationic site substitution in the “anti-zeolite” family of borates.
As the Eu content in the Sr(1) site increases, the A pseudolayer thickness (3.4 Å) does not change up to x = 0.20 (3.39 Å), while the B pseudolayer thickness, in which Sr(1) cations are located, increases insignificantly from 3.9 to 3.93 Å (Figure 4). When Eu3+ ions begin to occupy the Sr/Ba(1) site (x = 0.25), thicknesses of A and B pseudolayers (3.39 Å and 3.925 Å) practically do not change, which manifests itself in the appearance of an inflection on the dependence of the c parameter vs. Eu content (Figure 2). The equatorial bond lengths of the Sr(1)O7 polyhedra increase for Sr(1)–O(4) from 2.43(1) to 2.51(2) and decrease for Sr(1)–O(1) from 2.595(15) to 2.541(16) Å, respectively. The “apical” bonds of the Sr(1)–O(3) polyhedra decrease insignificantly from 2.686(15) to 2.669(16) (Sr(1)–O(3)) Å (Table 2).
In the Ba3Sr2.625Eu0.25B4O12 (x = 0.25) crystal structure, the Eu3+ ions occupy Sr(1) and Sr/Ba(1) sites, which leads to changes in the crystal structure. The Wyckoff letter and occupancy of the O(5) site became 16j and 0.75 instead of 32m and 0.375 in the Ba3(Sr3−1.5xEux)B4O12 (x = 0–0.20) solid solutions. In the Ba3Sr2.625Eu0.25B4O12 crystal structure, due to a change in the O(5) site symmetry, the B(4)–O(5) anion group is orientationally disordered over the 4 orientations (Figure 5, right center) instead of 8 orientations (left) in Ba3(Sr3−1.5xEux)B4O12 (x = 0–0.20). The Ba3Sr2.625Eu0.25B4O12 borate crystallizes in a new structure type (I4/mcm, a = 13.132, c = 14.633(4) Å, V = 2523.5 (11) Å3, Z = 8, R1 = 0.067) because the atomic sites are not the same as in the Ba3Sr3B4O12 crystal structure, although Ba3Sr2.625Eu0.25B4O12 and Ba3Sr3B4O12 crystallize in the same space group type. The difference between crystal structures is the different configuration of the disordered BO3 triangles in the channels along the c axis (Figure 5). Except for the “anti-zeolite” family, similar coordination of B–O environments has also been found in Ln14(GeO4)2(BO3)6O8 (Ln = Nd, Sm) [35], Li2Rb7Sr24(BO3)19 [36], Lu5Ba6(BO3)9 [37], Pb2(BO3)(NO3) [38], and Rb9Ba24(BO3)19 [39].
The 3Sr → 2Eu + □ substitution affects the increase in the size of the square cavity of the channels along the c axis. The internal diameter of Ba3Sr3B4O12, measured as the distance between the closest cations across the cavity, is 5.57 Å. This value provides a crystallographic free diameter of 4.13 Å, which is similar to those of the small-pore zeolites. A crystallographic free diameter was found by subtracting the averaged ionic radius of Sr and Ba for a coordination number of 7 from the distance between the closest cations across the cavity. The internal diameter and crystallographic free diameter of the channels of Ba3(Sr3−1.5xEux)B4O12 (x = 0.20) are 5.62 and 4.18 Å, respectively. In accordance with these data, we can control the size of the square tubes by substitution of the extrafamework cation sites by different cations.

3.4. Raman Spectroscopy

The Raman spectra of the Ba3(Sr3−1.5xEux)B4O12 (x = 0.01, 0.03, 0.06, 0.12, 0.15, 0.20, 0.25) samples are shown in Figure 6. All Raman bands observed in the spectra around 200, 400, 600, and 900 cm−1 correspond to vibrations of BO3 triangles [40]. No bands corresponding to BO4 tetrahedra were found in the Raman spectra, which agrees with structural data. The relatively large width of the Raman bands compared, for example, with LuBO3 single crystal, is explained by the disordered BO3 triangles in the channels along the c axis (Figure 6).

3.5. Absorption Spectroscopy

The absorption spectra of the Ba3(Sr3−1.5xEux)B4O12 samples were used to determine the optical band gap in Tauc plot coordinates. Figure 7a shows the example of the Tauc plot for the x = 0.01 sample. The dependence of the obtained optical band gap on the Eu3+ content is shown in (Figure 7b). Like the data in [34], the absorption edge shift depends on the degree of filling of the cationic framework with anionic clusters. The Sr → Eu substitution of the extraframework site affects the absorption edge shift too (Figure 7b). The band gap of the Ba3Sr3B4O12 is 6.10 eV [23] and the band gap for x = 0.01 is 3.80 eV. The band gap reduction may be due to the formation of defective localized states in the band gap upon the incorporation of Eu3+ ions.

3.6. Photoluminescence Properties

PLE and PE spectra of Ba3Sr3B4O12: Eu3+ samples are presented in Figure 8. All narrow bands observed in the spectra correspond to transitions of Eu3+ ions. The O2−–Eu3+ charge transfer excitation band is observed on PLE spectra below 300 nm. When the photoluminescence of europium is directly excited, the 7F0-5L6 transition is the most effective (Figure 8a). Therefore, PL spectra were obtained under 392 nm excitation.
Figure 8b clearly shows that with an increase in the concentration of active ions up to x = 0.20, the luminescence intensity increases. At a concentration of x = 0.25, the concentration quenching makes a significant contribution and the intensity of the luminescence decreases, as shown in the concentration dependence (Figure 9). If Eu3+ ions are distributed over cation sites, then concentration quenching occurs in Ba3Sr3B4O12:Eu3+ phosphors. Therefore, the main mechanism of concentration quenching is the dipole–dipole interaction between Eu3+ ions.
The lifetimes of the 5D0 level of Eu3+ ions were determined from the PL kinetic decay curves for the 5D0-7F2 transition upon excitation at 392 nm. The concentration dependence of obtained lifetimes is plotted in Figure 10. It can be seen that the 5D0 level lifetime of Eu3+ does not depend on the active ion concentration, which indicates the absence of additional channels of excitation or relaxation, such as energy or charge transfer.
The emission spectra were used to determine the chromaticity coordinates, the values of which are presented in Table 3. The Commission Internationale de I’Eclairage (CIE) diagram is presented in Figure 11. It can be seen that the increase in Eu3+ concentration leads to a shift in color to the red region.

4. Conclusions

A series of new Ba3(Sr3−1.5xEux)B4O12 (x = 0.01–0.25) red-emitting phosphors were obtained by crystallization from a melt. The crystal structures of Ba3(Sr3−1.5xEux)B4O12 (x = 0.03, 0.06, 0.15, 0.20, 0.25) phosphors were solved by the charge flipping method and refined in the tetragonal space group I4/mcm. The Eu3+ ions occupy the Sr(1) extraframework cationic site according to SCXRD data in the Ba3(Sr3−1.5xEux)B4O12 (x = 0.01–0.20). In the Ba3Sr2.625Eu0.25B4O12 crystal structure, the Eu3+ ions occupy Sr(1) and Sr/Ba(1) sites, which leads to changes in the crystal structure. The Ba3Sr2.625Eu0.25B4O12 borate crystallizes in a new structure type (I4/mcm, a = 13.132(3), c = 14.633(4) Å, V = 2523.5(11) Å3, Z = 8, R1 = 0.067). The Wyckoff letter and occupancy of the O(5) site are changed in the Ba3Sr2.625Eu0.25B4O12 crystal structure; B–O anion groups contain two BO3 triangles (B(3) and B(4)), orientationally disordered over the 4 orientations, and two ordered BO3 triangles (B(1) and B(2)).
Photoluminescence spectra of the Ba3Sr3B4O12: Eu3+ demonstrate that the characteristic lines correspond to the intra-configurational transitions inside Eu3+ ions. The optimal europium doping concentration is x = 0.20. If Eu3+ ions are distributed over cation sites, then concentration quenching occurs in Ba3Sr3B4O12:Eu3+ phosphors. Therefore, the main mechanism of concentration quenching is the dipole–dipole interaction between Eu3+ ions. Growth of the Eu3+ content leads to the change in CIE color coordinates from light red to red.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/sym15071399/s1. Table S1: Atomic coordinates, equivalent isotropic displacement parameters (Å2) and structural occupation factor for x = 0.03; Table S2. Anisotropic atomic displacement parameters (Å2) for x = 0.03; Table S3. Atomic coordinates, equivalent isotropic displacement parameters (Å2) and structural occupation factor for x = 0.06; Table S4. Anisotropic atomic displacement parameters (Å2) for x = 0.06; Table S5. Atomic coordinates, equivalent isotropic displacement parameters (Å2) and structural occupation factor for x = 0.15; Table S6. Anisotropic atomic displacement parameters (Å2) for x = 0.15; Table S7. Atomic coordinates, equivalent isotropic displacement parameters (Å2) and structural occupation factor for x = 0.20; Table S8. Anisotropic atomic displacement parameters (Å2) for x = 0.20; Table S9. Atomic coordinates, equivalent isotropic displacement parameters (Å2) and structural occupation factor for x = 0.25; Table S10. Anisotropic atomic displacement parameters (Å2) for x = 0.25.

Author Contributions

Writing—original draft, R.S.B., A.P.S., O.Y.S. and A.V.P.; Writing—review and editing, A.P.S., O.Y.S., S.K.F. and R.S.B.; Investigation, A.P.S., V.L.U., A.V.P., O.Y.S., S.N.V. and V.A.Y.; Project administration, A.P.S., O.Y.S. and R.S.B.; Data curation, A.P.S., R.S.B. and S.K.F.; Visualization, A.P.S., O.Y.S. and A.V.P.; Supervision, R.S.B. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Ministry of Science and Higher Education of the Russian Federation within the scientific tasks of the Institute of Silicate chemistry (Russian Academy of Sciences) [project number 0081-2022-0002] (synthesis), and the Russian Science Foundation [grant number 22-23-01133] (data evaluation and generalization, XRD and photoluminescence experiments, investigation of glasses, Raman and Absorption spectroscopy).

Data Availability Statement

Data Availability Statement: CCDC 2269856, 2269867, 2269885, 2269886, and 2269887 contain the crystallographic data for this paper. These data can be obtained free of charge via https://www.ccdc.cam.ac.uk/Community/Depositastructure/CSDCommunications/ (accessed on 25 November 2022).

Acknowledgments

The X-ray diffraction experiments were performed at The Centre for X-ray Diffraction Studies (Saint Petersburg State University). The Raman spectra and luminescence were collected at the Center for Optical and Laser Materials Research, Research Park of Saint Petersburg State University.

Conflicts of Interest

The authors declare no conflict of interest.

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Symmetry 15 01399 g001 550
Figure 1. Powder X-ray diffraction patterns of the Ba3(Sr3−1.5xEux)B4O12 phosphors. Red lines mark the calculated powder XRD pattern of Ba3Sr3(BO3)4.
Figure 1. Powder X-ray diffraction patterns of the Ba3(Sr3−1.5xEux)B4O12 phosphors. Red lines mark the calculated powder XRD pattern of Ba3Sr3(BO3)4.
Symmetry 15 01399 g001
Symmetry 15 01399 g002 550
Figure 2. Dependence of unit cell parameters vs. europium concentration x(Eu3+) in the Ba3(Sr3−1.5xEux)B4O12 phosphors.
Figure 2. Dependence of unit cell parameters vs. europium concentration x(Eu3+) in the Ba3(Sr3−1.5xEux)B4O12 phosphors.
Symmetry 15 01399 g002
Symmetry 15 01399 g003 550
Figure 3. DSC heating curves for (a) Ba3(Sr2.955Eu0.03)B4O12, (b) Ba3(Sr2.775Eu0.15)B4O12, and (c) Ba3(Sr2.625Eu0.25)B4O12.
Figure 3. DSC heating curves for (a) Ba3(Sr2.955Eu0.03)B4O12, (b) Ba3(Sr2.775Eu0.15)B4O12, and (c) Ba3(Sr2.625Eu0.25)B4O12.
Symmetry 15 01399 g003
Symmetry 15 01399 g004 550
Figure 4. Cationic pseudolayers in the Ba3(Sr2.70Eu0.20)B4O12 crystal structure.
Figure 4. Cationic pseudolayers in the Ba3(Sr2.70Eu0.20)B4O12 crystal structure.
Symmetry 15 01399 g004
Symmetry 15 01399 g005 550
Figure 5. The comparison of Ba3Sr3B4O12 (a) and Ba3Sr2.625Eu0.25B4O12 (b) crystal structures.
Figure 5. The comparison of Ba3Sr3B4O12 (a) and Ba3Sr2.625Eu0.25B4O12 (b) crystal structures.
Symmetry 15 01399 g005
Symmetry 15 01399 g006 550
Figure 6. Raman spectra of the Ba3Sr3B4O12:Eu3+ phosphors.
Figure 6. Raman spectra of the Ba3Sr3B4O12:Eu3+ phosphors.
Symmetry 15 01399 g006
Symmetry 15 01399 g007 550
Figure 7. Tauc plot for Ba3(Sr3−1.5xEux)B4O12 (x = 0.01) solid solution (a). Dependence of band gap on Eu3+ concentration for Ba3(Sr3−1.5xEux)B4O12 phosphors (b).
Figure 7. Tauc plot for Ba3(Sr3−1.5xEux)B4O12 (x = 0.01) solid solution (a). Dependence of band gap on Eu3+ concentration for Ba3(Sr3−1.5xEux)B4O12 phosphors (b).
Symmetry 15 01399 g007
Symmetry 15 01399 g008 550
Figure 8. PLE spectra at 613 nm emission (a) and PL spectra at 392 nm excitation (b) of Ba3(Sr3−1.5xEux)B4O12 phosphors.
Figure 8. PLE spectra at 613 nm emission (a) and PL spectra at 392 nm excitation (b) of Ba3(Sr3−1.5xEux)B4O12 phosphors.
Symmetry 15 01399 g008
Symmetry 15 01399 g009 550
Figure 9. Concentration dependence of the integrated luminescence intensity and PL quantum yield of Ba3(Sr3−1.5xEux)B4O12 samples.
Figure 9. Concentration dependence of the integrated luminescence intensity and PL quantum yield of Ba3(Sr3−1.5xEux)B4O12 samples.
Symmetry 15 01399 g009
Symmetry 15 01399 g010 550
Figure 10. Dependence of Eu3 + 5D0 level lifetime on Eu3+ concentration.
Figure 10. Dependence of Eu3 + 5D0 level lifetime on Eu3+ concentration.
Symmetry 15 01399 g010
Symmetry 15 01399 g011 550
Figure 11. CIE diagram of the Ba3(Sr3−1.5xEux)B4O12 phosphors.
Figure 11. CIE diagram of the Ba3(Sr3−1.5xEux)B4O12 phosphors.
Symmetry 15 01399 g011
Table
Table 1. Crystal data, data collection, and details of refinement of the Ba3(Sr3−1.5xEux)B4O12 phosphors.
Table 1. Crystal data, data collection, and details of refinement of the Ba3(Sr3−1.5xEux)B4O12 phosphors.
Eux0.030.060.150.200.25
Mr910.7911.3913.2914.2915.4
Crystal system, space groupTetragonal, I4/mcm
Temperature (°C)25
a, Å13.163 (3)13.154 (3)13.167 (3)13.151 (3)13.132 (3)
c, Å14.608 (4)14.612 (4)14.634 (4)14.653 (4)14.633 (4)
V, Å32531.1 (11)2528.3 (11)2537.0 (11) 2534.5 (11)2523.5 (11)
Z8
Radiation typeMo Kα
µ (mm−1)21.7621.7421.5421.4921.52
Crystal size (mm)0.08 × 0.13 × 0.150.07 × 0.12 × 0.130.10 × 0.12 × 0.140.10 × 0.09 × 0.150.11 × 0.13 × 0.17
DiffractometerRigaku XtaLab Synergy-S
No. of measured, independent, and observed [I > 3σ(I)] reflections24,289, 786, 53326,613, 807, 51227,486, 808, 61524,411, 633, 4519670, 776, 270
Rint0.1450.1160.1120.1740.148
(sin θ/λ)max (Å−1)0.7810.7770.7760.7770.777
R (obs), wR(obs), S0.070, 0.070, 2.200.051, 0.059, 1.830.051, 0.069, 2.890.058, 0.069, 2.420.068, 0.093, 1.02
No. of reflections787807808633776
No. of parameters6465646456
No. of restraints32224
Table
Table 2. Selected bond length (Å) in the Ba3(Sr3−1.5xEux)B4O12 structure.
Table 2. Selected bond length (Å) in the Ba3(Sr3−1.5xEux)B4O12 structure.
x0.030.060.150.20.25
Ba(1)–O(2) × 22.640 (12)2.616 (9)2.645 (9)2.671 (13)2.665 (15)
Ba(1)–O(1) × 42.791 (10)2.814 (7)2.814 (7)2.816 (10)2.822 (15)
<Ba(1)–O>62.742.752.762.772.77
Ba(1)–O(2)3.271 (14) × 23.266 (11) × 23.295 (10) × 23.270 (15) × 23.277 (18) × 2
<Ba(1)–O>82.872.882.892.892.90
Sr(1)–O(4)2.435 (10)2.428 (10)2.460 (11)2.484 (16)2.511 (18)
Sr(1)–O(1) × 22.595 (15)2.586 (10)2.588 (11)2.586 (15)2.541 (16)
Sr(1)–O(3) × 42.686 (14)2.655 (10)2.641 (10)2.660 (15)2.669 (16)
<Sr(1)–O>72.622.602.602.612.61
Sr/Ba(1)–O(5)2.42 (5)2.33 (4)2.45 (3)2.42 (5)2.297 (11)
Sr/Ba(1)–O(5)2.49 (4)2.56 (4)2.51 (4)2.60 (6)3.167 (4)
Sr/Ba(1)–O(5)2.57 (5)2.57 (3)2.50 (4)2.48 (6)-
Sr/Ba(1)–O(3)2.616 (13)2.604 (9)2.608 (10)2.593 (14)2.627 (16)
Sr/Ba(1)–O(2)2.641 (12)2.641 (9)2.628 (9)2.635 (13)2.631 (15)
Sr/Ba(1)–O(3)2.710 (15)2.740 (11)2.713 (12)2.738 (16)2.690 (16)
Sr/Ba(1)–O(6)2.84 (2)2.908 (18)2.88 (2)2.88 (3)2.62 (4)
Sr/Ba(1)–O(1)2.854 (10)2.828 (7)2.829 (7)2.826 (10)2.821 (15)
Sr/Ba(1)–O(6)2.86 (3)2.771 (17)2.81 (2)2.83 (3)2.62 (4)
Sr/Ba(1)–O(4)2.901 (10)2.897 (8)2.897 (8)2.889 (11)2.892 (14)
Sr/Ba(1)–O(3)3.083 (14) 3.117 (11)3.142 (11)3.133 (15)3.115 (17)
<Sr/Ba(1)–O>112.732.722.722.732.75 *
B(1)–O(2)1.36 (3)1.37 (2)1.363 (18)1.30 (4)1.37 (4)
B(1)–O(3) × 21.37 (3)1.37 (2)1.394 (17)1.39 (3)1.35 (4)
<B(1)–O>31.361.371.3831.361.36
B(2)–O(1) × 21.39 (2)1.36 (4)1.36 (2)1.33 (3)1.36 (3)
B(2)–O(4)1.30 (2)1.38 (5)1.35 (2)1.38 (3)1.36 (3)
<B(2)–O>31.361.371.361.351.36
B(4)–O(6) × 41.40 (3)1.45 (2)1.42 (2)1.41 (3)1.51 (5)
<B(4)–O>41.401.451.421.411.51
B(3)–O(5)1.37 (3) × 81.41 (3) × 81.41 (3) × 81.39 (4) × 81.40 (2) × 4
<B(3)–O>81.371.411.411.391.40 **
* <Sr/Ba(1)–O>10. ** <B(3)–O>4.
Table
Table 3. CIE (CIE 1931) chromaticity coordinates of the Ba3Sr3B4O12:Eu3+ phosphors.
Table 3. CIE (CIE 1931) chromaticity coordinates of the Ba3Sr3B4O12:Eu3+ phosphors.
C (Eu3+)xy
0.010.4490.319
0.030.4150.310
0.060.5090.330
0.120.5910.343
0.150.5860.342
0.20.6230.346
0.250.6230.346
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Bubnova, R.S.; Shablinskii, A.P.; Povolotskiy, A.V.; Shorets, O.Y.; Ugolkov, V.L.; Volkov, S.N.; Yukhno, V.A.; Filatov, S.K. Novel “Anti-Zeolite” Ba3Sr3B4O12: Eu3+ Phosphors: Crystal Structure, Optical Properties, and Photoluminescence. Symmetry 2023, 15, 1399. https://doi.org/10.3390/sym15071399

AMA Style

Bubnova RS, Shablinskii AP, Povolotskiy AV, Shorets OY, Ugolkov VL, Volkov SN, Yukhno VA, Filatov SK. Novel “Anti-Zeolite” Ba3Sr3B4O12: Eu3+ Phosphors: Crystal Structure, Optical Properties, and Photoluminescence. Symmetry. 2023; 15(7):1399. https://doi.org/10.3390/sym15071399

Chicago/Turabian Style

Bubnova, Rimma S., Andrey P. Shablinskii, Alexey V. Povolotskiy, Olga Yu. Shorets, Valery L. Ugolkov, Sergey N. Volkov, Valentina A. Yukhno, and Stanislav K. Filatov. 2023. "Novel “Anti-Zeolite” Ba3Sr3B4O12: Eu3+ Phosphors: Crystal Structure, Optical Properties, and Photoluminescence" Symmetry 15, no. 7: 1399. https://doi.org/10.3390/sym15071399

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