Synthesis and Photoluminescence Properties of Rare-Earth-Activated Sr_3–xA_xAlO₄H (A = Ca, Ba; x = 0, 1): New Members of Aluminate Oxyhydrides

Abstract

A series of aluminate-based oxyhydrides, Sr 3−x A x AlO 4 H (A = Ca, Ba; x = 0, 1), has been synthesized by high-temperature reaction of oxide and hydride precursors under a H 2 atmosphere. Their crystal structures determined via X-ray and neutron powder diffraction are isostructural with tetragonal Sr 3 AlO 4 F (space group I4/mcm), consisting of (Sr 1−x/3 A x/3 ) 2 H layers and isolated AlO 4 tetrahedra. Rietveld refinement based on the diffraction patterns and bond-valence-sum analysis show that Ba preferentially occupies the 10-coordinated Sr1 sites, while Ca strongly prefers to occupy the 8-coordinated Sr2 sites. Luminescence owing to the 4f−5d transition of Eu 2+ or Ce 3+ was observed from Eu-and Ce-doped samples, Sr 3−x−y A x B y AlO 4 H (A = Ca, Ba; B = Eu, Ce; x = 0, 1, y = 0.02), under excitation of near-ultraviolet light. Compared with its fluoride analogue, Sr 3 AlO 4 H:Ce 3+ shows red shifts of both the excitation and emission bands, which is consistent with the reported hydride-based phosphors and can be explained by the covalency of the hydride ligands. The observed luminescence spectra can be decomposed into two sets of sub-bands corresponding to Ce 3+ centers occupying Sr1 and Sr2 sites with distinctly different Stokes shifts (1.27 and 0.54 eV, respectively), as suggested by the results of constrained density functional theory (cDFT). The cDFT results also suggest that the large shift for Ce 3+ at Sr1 is induced by large distortion of the coordinated structure with shortening of the H−Ce bond in the excited state. The current findings expand the class of oxyhydride materials and show the potential of hydride-based phosphors for optical applications.

Expanding the hydride chemistry: antiperovskites A3MO4H (A = Rb, Cs; M = Mo, W) introducing the transition oxometalate hydrides

“…The assigned glazer tilt notation is a 0 a 0 c − . 27 In addition to the prototype K 3 SO 4 F, 26 several compounds with tetrahedral complex anions are known to crystallize in this structure-type such as the selenate fluoride K 3 SeO 4 F, 28 the oxonitrodosilicates Ln 3 [SiN 3 O]O (Ln = La, Ce, Pr), 29 or the aluminate hydride Sr 3 AlO 4 H. 19 A schematic of the crystal structure of the tetragonal phases can be found in the ESI in Fig. S9.…”

“…The reductive nature of hydrogenation reactions oen requires carefully designed synthetic routes to keep the complex anions intact. In turn, only a handful mixed anionic hydrides with complex (oxo-)anions, such as aluminate hydrides 18,19 or borate hydrides 7 are reported to date. The combination of complex oxoanions of transition metals with hydrides has not yet been realized to date.…”

Na3SO4H—The First Representative of the Material Class of Sulfate Hydrides

“…Very recently the novel material classes of phosphate hydrides, [15, 16] silicate hydrides, [17, 18] and borate hydrides [19] were also discovered. Some mixed anionic hydrides, such as silicate hydrides, borate hydrides, oxide hydrides, and halide hydrides, also allowed for tuning of bright rare earth ion luminescence [17–25] . Encouraged by these recent breakthroughs in an emerging field, we aimed to broaden our search for yet‐to‐be‐discovered anion combinations with possibly unique chemical and physical properties.…”

Na3SO4H – ein erster Vertreter der Materialklasse der Sulfathydride

“…Erst kürzlich wurden die neuen Materialklassen der Phosphathydride, [15, 16] Silikathydride [16, 17] und Borathydride [19] entdeckt. Manche dieser gemischt‐anionischen Hydride, wie die Silikathydride, Borathydride, Oxydhydride und Halogenhydride, erlauben zudem eine Modifizierung hell leuchtender, Seltenerd‐aktivierter Lumineszenz [17–25] . Motiviert von diesen jüngsten Durchbrüchen in einem aufstrebendem Feld, erweiterten wir die Suche nach bis jetzt unbekannten Anionenkombinationen mit möglicherweise einzigartigen chemischen und physikalischen Eigenschaften.…”

“…Manche dieser gemischt-anionischen Hydride, wie die Silikathydride, Borathydride, Oxydhydride und Halogenhydride, erlauben zudem eine Modifizierung hell leuchtender, Seltenerd-aktivierter Lumineszenz. [17][18][19][20][21][22][23][24][25] Motiviert von diesen jüngsten Durchbrüchen in einem aufstrebendem Feld, erweiterten wir die Suche nach bis jetzt unbekannten Anionenkombinationen mit mçglicherweise einzigartigen chemischen und physikalischen Eigenschaften. Ein mçglicher Kandidat schien hierbei eine Verbindung zwischen Sulfatund Hydridanionen zu sein, was jedoch eine synthetische Herausforderung darstellt, denn zu harsche Reaktionsbedingungen kçnnten zu einer Reduktion von Sulfationen anstatt zu der gewollten Herstellung eines gemischt-anionischen Sulfathydrids führen.…”