Eu2+掺杂碱土金属氢化物氯化物AE7H12Cl2（Ae=Ca和Sr）中光学特性检测方案(激光产品)

智能文字提取功能测试中

ACCEPTED MANUSCRIPT Author’s Accepted Manuscript Synthesis and Optical Properties of the Eu2+-Doped Alkaline-Earth Metal Hydride ChloridesAE-H12Cl2 (AE=Ca and Sr) Daniel F i， Thomas Wylezich， Atul D.Sontakke， Andries Meijerink， Philippe Goldner，Philip Netzsch， Henning A. HoppeN，athalieKunkel， Thomas Schleid www.elsevier.comlocate/jlumin PII： S0022-2313(18)31257-2 DOI： https：//doi.org/10.1016/j.jlumin.2019.01.033Reference： LUMIN16231 To appear in：：JJournal ofLuminescence Received date： 11 July 2018 Revised date：15 November 2018 Accepted date：16 January 2019 Cite this article as： Daniel Rudolph， Thomas Wylezich， Atul D. Sontakke，Andries Meijerink， Philippe Goldner， Philip Netzsch， Henning A. Hoppe，Nathalie Kunkel and Thomas Schleid， Synthesis and Optical Properties of theEu+-Doped Alkaline-Earth Metal Hydride Chlorides AE-H12Cl2 (AE = Ca andSr)， Journal ofLuminescence， https：//doi.org/10.1016/j.jlumin.2019.01.033 This is a PDF file of an unedited manuscript that has been accepted forpublication. As a service to our customers we are providing this early version ofthe manuscript. The manuscript will undergo copyediting， typesetting， andreview of the resulting galley proof before it is published in its final citable form.Please note that during the production process errors may be discovered whichcould affect the content， and all legal disclaimers that apply to the journal pertain. Synthesis and Optical Properties of the Eu -Doped Alkaline-Earth Metal Hydride ChloridesAE-H12Cl2 (AE=Ca and Sr) Daniel Rudolph， Thomas Wylezich， Atul D. Sontakke ， Andries Meijerink， Philippe Goldner， PhilipNetzsch， Henning A. Hoppe， Nathalie Kunkel， Thomas Schleid* University of Stuttgart， Institute for Inorganic Chemistry，Pfaffenwaldring 55， 70569 Stuttgart， Germany Technical University of Munich， Chair for Inorganic Chemistry with Focus on Novel Materials， Lichtenbergstr.4， 85748 Garching， Germany Utrecht University， Debye Institute， P.O. Box 80 000， 3508 TA Utrecht，Netherlands "PSL University， Chimie ParisTech， CNRS， Institut de Recherche de Chimie Paris， 75005 Paris， FranceUniversitat Augsburg， Institut fur Physik， Universitatsstr. 1， D-86159 Augsburg， Germany nathalie.kunkel@lrz.tu-muenchen.de schleid@iac.uni-stuttgart.de Corresponding author. Technical University of Munich， Chair for Inorganic Chemistry with Focus on NovelMaterials， Lichtenbergstr. 4，85748 Garching， Germany. Tel.： +49 89 289 13109； fax： +49 89 289 13186Corresponding author. University of Stuttgart， Institute for Inorganic Chemistry， Pfaffenwaldring 55， 70569Stuttgart， Germany， Tel.： +49-711-685-64240； fax： +49-711-685-64241 Abstract In our study of the optical properties of Eu -doped alkaline-earth metal hydride chlorides AE-H12Cl2 (AE= Caand Sr) we observe yellow (AE=Sr) and orange-red (AE=Ca) emission. Compared to the emission energies ofEu +- doped fluorides， chlorides and mixed fluoride chlorides， this corresponds to a wide redshift 2+of the Eu4f5d'-4f’ emission. We explain this observation with the strong polarizability of the hydride anion and thereforeits strong nephelauxetic effect， which shifts the 5d barycenter to lower energy. Furthermore， the redshift is evensignificant compared to other known hydride chlorides and hydride oxide chlorides， which is probably caused bythe relatively short AE /Eu -H distances， or it might also be caused by impurity-trapped exciton states. Wehave also investigated the temperature dependence of the photoluminescence lifetimes and the thermal stability.Even though the compounds are probably not ideal for phosphor application due to their low stability against airand moisture， our study underlines the large influence of the highly polarizable hydride anion on the opticalproperties of divalent europium and shows that Eu could be used as a probe in mixed anionic system todetermine the hydride content. e Keywords： Hydride Chlorides， Eu Luminescence， Alkaline-Earth Metals 1.IIntroduction The crystal chemistry and properties of alkaline-earth metal fluoride halides， which crystallize with the PbFCl-type structure， have been investigated elaborately during the course of many years [1-4]. Especially theBaFX：Eu series(X=Cl， Br， I) has received a lot of attention， since it can be used as storage phosphor in imageplates for X-ray and neutron detectors [5-7]. A large number of investigations on its luminescence propertiesand， most of all， possible storage mechanisms have been carried out [8-10]. But not only pure halides are knownin these systems. In the attempt to synthesize subhalides of the alkaline-earth metals， such as the so-calledcalcium monochloride [11]， Ehrlich et al. discovered the hydride halides [12-14]] and later， also thecorresponding hydride halides of some divalent rare-earth metal ions were found [15，16]. These hydride halidesMHX (M=Ca， Sr， Ba， Eu， Yb， Sm； X= Cl， Br， I) have since then been thoroughly characterized [17] andadditionally， a number of further compounds in the phase diagram MH2-MX2(M=Ca， Sr， Ba， Eu；X=Cl， Br， I)，such as CazH12Cl2 [18]， CazHBr [18]， Sr-H12X2 (X=Cl， Br) [19]， SrHgI [20]， BazHX (X=Cl， Br， I) [21，22] orEuzH；Cl [23] have been discovered. While many optical investigations on fluoride halides doped with rare-earthmetal cations have been carried out， the corresponding hydrides have received little attention. The onlyluminescence studies on hydride chlorides so far have been reported for EuHCl [24] and LiEu2HOCl2 [25]. Yet， luminescence spectroscopy of rare-earth metal ions showing 4f-5d transitions can reveal important informationregarding the polarizability of the surrounding anions. This is because the 5d levels are not shielded but fullyexposed to the orbitals of the ligands， so that both， the crystal field splitting as well as the nephelauxetic effect，play an important role. For instance， Euions doped into nitridosilicates show a significant redshift of thebarycenter of the 5d levels and the emission energies [26， 27] compared to less polarizable anions [28]. Anotheranion with a high polarizability is hydride. Lately， photoluminescence [29， 30] and thermoluminescence [31] inEu -doped hydrides have been studied and it was found that the high polarizability leads to an extreme red shiftof the barycenter of the 5d levels. As a consequence， it is possible to vary the emission energy by variation ofthehydride content in mixed-anionic hydride fluorides [32-34]， which then corresponds to tuning the polarizabilityof the chemical environment. It can therefore be expected that the Eu’emission energies in the hydride halideswill show a redshift compared to the fluoride halides. Here， we study the Eu luminescence in the doped hydridechlorides CazH12Clz：Euand SrzH12Clz：Eu. 2. Experimental section 2.1 Synthesis Due to their moisture and air sensitivity， the starting materials and products were handled in an argon-filledglovebox (GS Glovebox Systemtechnik). To ensure a homogeneous distribution of europium atoms in thealkaline-earth metal (w(Eu)=0.5 mol-%)， pieces of europium (Eu： 99.9%， ChemPur) and the respectivealkaline-earth metal (Ca： 99，98 %， Sr： 99 %， both Alfa-Aesar) were fused several times by arc-welding themetals under argon in the glovebox. For the calcium compound， 165 mg of the calcium-europium mixturereacted with 46 mg of sodium amide (Na[NH2]： self-made)，63 mg sodium chloride (NaCl：99，99 %， Merckusing 130 mg of sodium (Na： ACS grade， Alfa Aesar) as a flux. To obtain the strontium compound， 211 mg ofthe strontium-europium mixture and 47 mg of ammonium chloride ([NH4]Cl： for analysis， Merck)， strontiumchloride (SrCl ： 99，99 %， Alfa Aesar) and sodium each were used. After transferring the reactants into niobiumcapsules， which were cleaned prior to use in a mixture of sulfuric， nitric and hydrofluoric acid， they were arc-welded under helium. To prevent their oxidation， the niobium capsules were enclosed into evacuated silicaampoules and tempered in a muffle furnace at 900 °℃ for 24 (CazH12Cl2) or 12 hours (Sr Hi2Cl2). While up to2 mm long crystals of the strontium compound were obtained without a special cooling procedure by justswitching off the furnace， the calcium compound only formed in sufficiently large crystals after cooling downwithin 72 hours to room temperature. Since sodium was used as a flux， it had to be removed by dissolving it in liquid ammonia using a tensi-eudiometer [35]. The opened niobium capsule was placed in an H-shaped glass tube that could be connected viaa flange to the tensi-eudiometer， which was filled with gaseous ammonia after evacuating. By using an ethanol-dry ice cooling bath liquid ammonia could be condensed into the H-shaped tube and the sodium dissolved.Afterwards， the dark blue sodium solution was poured into the second leg of the H-shaped tube by holding ithorizontally. By gentle heating of the sodium solution， the ammonia evaporated and the whole procedure wasrepeated， until the liquid ammonia merely showed a faint blue color. After evacuating the tube again， it could bebrought into the glove box， where crystals of the hydride chlorides could be selected for single-crystal X-raydiffraction and the luminescence measurements. 2.2 Characterization 2.2.1 Single-crystal X-ray diffraction For both compounds， CazHi2Cl：Eu and SrH12Cl：Eu， several single crystals were selected under a lightmicroscope (M60， Leica Microsystems) in the glove box and put into thin-walled glass capillaries (Hilgenberg)with a diameter of 0.1 mm. The so prepared single crystals could be used to determine unit-cell parameters on aK-CCD diffractometer (Bruker-Nonius) in order to verify the successful synthesis of the desired alkaline-earthmetal hydride chlorides. 2.2.2 Optical measurements Due to air and moisture sensitivity， the crystals were enclosed into silica ampoules with 5 mm diameter for alloptical measurements. Photoluminescence spectra were recorded with a tunable optical parametric oscillatorpumped by a neodymium-YAG laser (Ekspla NT342B-SH with 6 ns pulse lengths) together with a Jobin-YvonHR250 monochromator (600 grooves/mm) and a PI-MAX ICCD camera (Princeton Instruments) for detection. Samples were excited at 365 nm. To increase the signal-to-noise ratio， 100 accumulations were collected permeasurement. For temperature dependent measurements， the samples were placed into a Janis closed-cyclehelium cryostat with a Lakeshore temperature controller. Samples were fixed to the cold finger using high puritysilver paint and copper foil. Decay measurements were recorded on the same set-up. Data were recorded 50 nsafter the laser pulse and up to 5 us delays with an integration window of 20 ns. Photoluminescence excitationspectra at room temperature were recorded using a Xe plasma lamp (Energetic EQ99X) with a Jobin-Yvon HR250 monochromator (1200 grooves/mm) for excitation and an Acton Spectra Pro 2150 Dual GratingMonochromator together with a Pixis 100 CCD camera for emission. All spectra were corrected for lampintensity. Further photoluminescence and thermoluminescence measurements were carried out on a EdinburghInstrument FLS920 spectrofluorometer equipped with a double monochromator for the excitation beam (Czerny-Turner， 300 mm focal length) and a monochromator for UV/Vis detection. The sample was excited with a 450 WXenon lamp and a Hamamatsu R928 photomultiplier tube (PMT) was used for the emission signal detection. Forthermoluminescnce， the samples were cooled down to 4K， irradiated with 365 nm Hg lamp for three minutes andthen the thermoluminescece was investigated in the temperature range from 4K to 297K. Low temperaturemeasurements were carried out in an Oxford instruments liquid helium flow cryostat. 3. Results and discussion 3.1 Crystal Structure The crystal structure of both hydride chlorides AE-H2Cl (AE = Ca and Sr) was already described inreferences [18] and [19] and is isostructural to the ordered variant of the barium fluoride chloride BazF12Cl2in the space group P6 [36]， where also the structural model for the hydride compounds was taken frombecause no accurate positions for the hydride anions in AE-H12Cl2 representatives exist due to the lack ofneutron diffraction studies. Since the coordination spheres of the three crystallographically different alkaline-earth metal cations by the anions are important for the luminescence studies， they will briefly be discussedhere. All three AEcations are surrounded by nine anions forming tricapped trigonal prisms. While (AE1)2is solely coordinated by hydride anions， the coordination spheres of (AE2)and (AE3)2 are built up byseven H and two Cl anions (Figure 1). Fig 1： Coordination polyhedra [(AE1)H] (left) and [(AE2/AE3)H，Cl2](right) in the crystal structure of the hydridechlorides AE-H12Cl2 (AE=Ca and Sr). 3.2 Photoluminescence and Absorption Under UV excitation， SrzHj2Cl：Eu’shows a bright yellow emission， while the emission of CazH12Cl：Eu israther orange-red (Figure 2). ACCEPTED MANUSCRIPT Fig 2： Single crystals of SrHi2Cl：Eu*(left) and CajH12Clz：Eu*(right) under UV light. At room temperature， SrzH12Cl：Eu shows a broad band emission with a maximum at 595 nm (Figure 3a)，which is assigned to the Eu²4f 5d-4f transition. At low temperatures， higher intensities are observed and themaximum is slightly shifted to lower wavenumbers. From about 125 K onwards， the intensities decreasesignificantly with increasing temperature. The broad band emission is due to the existence of two types of cationsites in the crystal structure， the two similar cation sites with a coordination by seven hydride and two chlorideanions and the third cation site coordinated exclusively by nine hydride anions. It can be expected that theemission from the site coordinated exclusively by hydride anions is red-shifted compared to the sites coordinatedby seven hydride and two chloride anions. This is because the impact of the high polarizability of the hydrideligand is expected to be large [29]. Figure 3： Temperature-dependent photoluminescence emission spectra ofa) Eu-doped SrzH12Cl2(0.6 mol-%Eu) and b)CazH12Cl2 (0.6 mol-%Eu ). The reason for the slight blue-shift with increasing temperature is probably the existence of the different latticesites and their possible different temperature-dependent behavior. In former studies on Euin hydridic materials[29] it was shown that the mechanism of thermal luminescence quenching is likely to be thermally activatedphotoionization. Here， the emitting 4f°5d excited state is located just below the conduction band. The emissionis then quenched by thermally activated ionization from the excited state to the conduction band. This model isin good agreement with the rather small bandgap of hydrides [37] compared to halides or oxides. Assuming thatthermal quenching occurs at slightly lower temperatures for the cation site surrounded by nine hydride anions，this might also explain why the peak maximum of the broad band emission is located at 605 nm at lowtemperatures and shifts to 595 nm at higher temperatures. The observed broad band emission can be coconsideredan envelope curve comprising the emission peaks of both cation sites， which are too close to each other to beclearly separated. If the intensity of the lower energy emission maximum decreases faster with increasingtemperatures than the higher energy emission maximum， this will lead to an apparent blue-shift of the total emission band. Deconvoluted emission curves and further luminescence spectra can be found in Figure S1 in theElectronic Supporting Information. Another possible explanation is the presence of impurity-ascribed exciton states. Dorenbos suggests that such ablue-shift， as it is observed for e. g. CsCaFs：Eu’ and KCaFs：Eu [38]， is accomplished by thermal activationfrom the impurity-trapped exciton state to the 5d state [39]. Eu’ might be oxidized to Eu’ with a trappedelectron in the surrounding or other defects might be present. In NaCl-type alkali-metal halides [40] andalkaline-earth metal fluoride halides [41-42] different types of defects， such as F-centers (electrons trapped athalide-ion vacancies)， Frenkel defects on the larger halide lattice site， or self-trapped holes have been observedand modelled. In BaFCl anionic conduction via halide vacancies was observed and it was clarified that thermallygenerated lattice defects are of Schottky type [43]. For ionic hydrides， little is known about defect formation， butconsidering the so-called hydride-fluoride analogy [44-45] of these compounds， it may be suggested that similardefects also occur in hydrides. Possible defects might， for example， be an electron trapped on anion vacancies orhydride anions on chloride sites. However， thermoluminescence measurements in the range between 4 K androom temperature did not show any thermoluminescence emission. This may either be explained by the absenceof glow peaks or because only small amounts of small single crystal samples were available. In Figure 3b， the temperature-dependent photoluminescence spectra of Eu in the corresponding calciumhydride chloride are shown. As in the case of the strontium compound， a very broad band with a maximum at600 nm is observed at room temperature. Similar to the strontium compound， the Euemission peaks from thetwo different lattice sites are not clearly separated. The intensities increase with decreasing temperature. Incontrast to the strontium compound， these two emission peaks start to be separated at very low temperatures.Starting from 70 K， it is possible to clearly distinguish between two apparent peak maxima at 590 and 615 nmSimilar to the strontium compound， the peak at lower energy is more intense at low temperatures， but itsintensity decreases faster with increasing temperatures. As already discussed for the strontium compound， thetwo emission peaks are assigned to the two different local environments， two similar sites coordinated by sevenhydride and two chloride anions and a third site coordinated exclusively by hydride anions. The observation ofseveral emission peaks is not unexpected， as a similar behavior of the luminescence emission spectra is alsofound for Eu -doped BazF12Cl2 [47， 48]. In case of the fluoride chloride， the overlaying emission maxima leadto the total impression of a white-emitting phosphor. The excitation spectra measured at room temperature for different emission wavelengths (570， 600， and 650 nm)are shown in the Figures 4a and 4b. While the excitation spectra of Eu-doped BazF12Cl [46， 47] differsignificantly for the different emission wavelengths， the excitation spectra of the hydride chlorides do not showsuch marked differences. The intensities slightly differ， but the peak positions still remain the same. Bothcompounds show a maximum at 350 nm in their excitation spectra， with small shoulder at 275 nm and anotherone at 400 nm. Fig 4： Room-temperature photoluminescence excitationng，spectra(of a)SrH12Cl：Eu*(0.6) mol-% Eu *) andbCazH12Clz：Eu*(0.6mol-%Eu). In the Figures 5a and 5b， the temperature-dependent decay curves are depicted for Eu in Sr-Hi2Cl andCaH12Cl2. At low temperatures， the decays show only a slight deviation from single exponential behavior. Fig 5： Temperature-dependent decay curves ofa) Eu’*-doped SrHi2Cl (0.6 mol-%Eu ) and CanH2Clz(0.6mol-%Eu’t). With increasing temperature， the lifetimes become significantly shorter and the deviation from a singleexponential decay appears larger. For the Eu emission in Sr-H12Cl a lifetime of 780 ns is found. The lifetimesbecome significantly shorter starting from 125 K and at room temperature， 590 ns is finally found (Figure 6). The lifetime of the Euemission in CazH2Cl2 at low temperatures is 645 ns. Above 125 K it decreases rapidlyand reaches 400 ns at room temperature. These values are in the range of the lifetimes found for the parity-allowed 4f'5d'-4f’ (’sr2) emission of divalent europium in hydrides [29， 48] and somewhat shorter than in otherclasses of materials emitting at comparable energies [49]. A possible explanation is the high refractive index n ofhydride compounds [50] compared to other materials such as fluorides or oxides [51]. It is well known that therefractive index has a strong influence on the radiative decay rate [52， 53]. Many studies on this dependencehave already been carried out， for example on the changes in the radiative lifetime of 4f-4f emissions uponchanging the particle sizes [54]， which corresponds to a change in the refractive index， or on local field effectsinfluencing the radiative lifetime of the 5d-4f emission of Ce’ in different hosts [55]. An increase in therefractive index of the system will lead to a faster radiative decay rate， which is consistent with the observedshorter lifetimes for Eut emissions in hydride chlorides. The deviation from single-exponential behavior may bedue to the different lattice sites with different thermal quenching behavior. Additionally， the presence of defectsinfluencingthe opticalpropertiescannottbeecompletelyyexcluded，but seemsunlikely， since nothermoluminescence glow peaks were observed. Fig 6： Temperature dependence of the integrated photoluminescence emission intensities and the decay times ofEu -dopedSrHi2Cl2(0.6mol-%Eu*) In the Figures 6 and 7， the temperature dependence of the integrated intensities and the lifetime of the Euemission in Sr-H2Cl and CaHi2Cl2 are shown.The decrease of the intensities and lifetimes with increasingtemperature can be clearly seen， however， a determination of the exact quenching temperature is hampered， sincethe different emission peaks of the three different lattice sites cannot clearly be separated from each other. anuscf Fig 7： Temperature dependence of the integrated photoluminescence emission intensities and the decay times ofEu -dopedCazH12Cl2(0.6 mol-%Eu ) For comparison， Table 1 compiles the emission maxima of different hydride compounds together with thecoordination numbers of the Eu+ cations and the Eu-H distances. It can be seen that the emission maxima shiftto longer wavelengths for decreasing coordination numbers of the Eucations and also for decreasing Eu-Hbond lengths， which is for example true for calcium compared with strontium compounds. It can easily beexplained by the smaller ionic radius of Cacompared to the heavier alkaline-earth metal cations and thereforesmaller unit-cell parameters. These effects lead to a larger ligand-field splitting， which causes a smaller energygap between the lowest 5d excited state [Xe]4f 5d ofEu and the 4f’(’S7/2) ground state [57]. Due to the strongnephelauxetic effect of the hydride ligand [29]， which leads to a lowering of the barycenter of the 5d orbitals[58]， the hydride-rich hydride chlorides AE-H12Cl2 (AE=Ca and Sr) and the pure alkaline-earth metal hydridesAEH with comparably small coordination numbers and Eu-H distances show the most red-shifted Euemissions for all hydrides that have so far been investigated. Compared to fluorides， chlorides and fluoridechlorides， the redshift observed in the Eu’ emission is remarkable [57]. For instance， SrFCl：Eu²+ shows anemission at 388 nm [57， 59] and CaFCl：Eu+ at 396 nm [57， 60， 61]. Also， the Eu-doped pure chlorides andfluorides of strontium and calcium emit in the UV-blue color region [59]. A more detailed over view on the sofar investigated rare earth metal ion - doped hydrides and mixed anionic hydrides can be found in Ref. [62]. Table 1： Comparison ofthe maximum emission wavelengths， the coordination number (CN) ofEu *and the metal-hydridebond lengths d(Eu-H) in selected hydride compounds. Compound em， max / nm CN(Eu) d(Eu-H)/pm (average) Eu2H3CI [23， 56 503 10 240-277 (256) KMgHF2 331 505 12 282 EuHC1 241 515 9 248 KMgH3 481 565 12 285 LiSrH：Eu+ 291 570 12 271 EuH，F2-x 321 570-685 8 253 LiEuHOCl 251 581 9 261-273 (267) SrzH12Cl2 [this work] 595 9 224-284 (257) CazH12Cl2 this work] 600 9 223-257(242) SrHo.5F1.5 [331 600 8 252 SrH2 [37] 728 9 243-284(260) CaH， 371 764 9 205-270(234) a Eupresumably on theposition of K . Conclusions In summary， we have studied Eu photoluminescence in the Eu -doped hydride chlorides AE-H12Cl2 (AE= Caand Sr) and observed yellow (AE=Sr) and orange-red (AE =Ca) emission. This corresponds to a stronger red-shift compared to emission energies usually observed for Eu *-doped fluorides， chlorides and fluoride chlorides.and even compared to several other hydride chlorides and hydride oxide chlorides. We explain this astonishingobservation with the high polarizability of the hydride anion and therefore a strong nephelauxetic effect， whichshifts the 5d barycenter to lower energy. Furthermore， the AE /Eu-H distances are comparably small， whichis also expected to lead to a large crystal field splitting. Consequently， our study confirms the large influence ofthe highly polarizable hydride anion on the emission energies of divalent europium. Thus， it might also beinteresting to study mixed hydride fluoride chlorides， such as AEH12-xF.Cl in order to tune the emissionproperties in the future. Even though pure hydrides are not expected to be very air- and thermally stable， Euluminescence might also be used to determine the hydride content in such mixed anionic systems and it ispossible that some systems with low hydride content show a higher stability. Especially some hydride oxides(“oxyhydrides) are not sensitive against air- and moisture. With regard to the use of comparable fluoridechlorides as storage phosphors and possible defect formation， it might be worthwhile to also carry out furtherthermoluminescence studies in these hydride chloride systems. Such studies -as already done for nitridosilicates[26]-might yield helpful information on so far little studied defect formation mechanisms in hydrides. Acknowledgments We thank Jean-Francois Engrand for constructing a sample holder for low-temperature photoluminescencemeasurements using ampoules and Sacha Welinski for support. N. K. and T. W. thank the Fonds derChemischen Industrie for a Liebig and a doctoral fellowship (Li 197/02) and Prof. Dr. Thomas Fassler forhosting their group. P.N. also thanks the Fonds der Chemischen Industrie for a doctoral fellowship. The researchleading to these results has received funding from the DFG (KU 3427/4-1)， and the Bavarian-French AcademyCenter (mobility aid， grant no. Az. FK03_2017). We further thank Prof. Dr. Rainer Niewa for providing ussodium amide and permitting us to use his tensi-eudiometer as well as Dr. Falk Lissner for the single-crystal X-ray diffraction measurements. ( References ) ( [1] M. Sauvage， Acta Crystallogr. B 30 (1974)2786-2787. ) ( [2] V. G. Lambrecht， JR.， M. R obbins， R. C. S herwoord， J. Solid State Chem. 1 0 (1974) 1 - 4. ) ( [3] H .P. Beck， J. Solid State Chem. 17 (1976)275-282. ) ( [4] H. P. Beck， Z. Anorg. Allg. Chem. 451 ( 1979) 73-81. ) ( [5] Y. Amemiya， J. M iyahara， Nature 336 (1988)89-90. ) ( [6] N. Niimura， Y. K arasawa， I. Tanaka， J . Miyahara， K. Takahashi， H. Sa i to， S. Koizumi， M. Hid a ka， Nucl. Instrum. Methods A 349 (1994) 521-525. ) ( [7] K. Takahasi， J. Lumin. 160 (2002)307-315. ) ( [8] K . Takahashi， K. K o hda， J. M i yahara， Y. Kanecitsu， K. Am i tani， S. Shionaya， J. L u min. 31 - 32 (19 8 4) 266-268. ) ( [9] H. von Seggern， T. Voight， W. Knupfer， G. L a nge， J. Appl. Phys. 64 (1988) 1405-1412. ) ( [ 1 0] H. H. R iter， H . von Seggern， R. R e ininger， V. Saile， P h ys. Rev. Le t t. 6 5 (1990) 24 3 8-2441. ) ( [ 1 1] L . Wohler， G. Rodewald， Z . Anorg. Allg. Chem. 61 (1909) 54-90. ) ( [1 2 ] P. Ehrlich， B. Alt， L. Gentsch， Z. Anorg. Allg. Chem. 2 8 3 (1956) 58-73. ) ( [ 1 3 ]P. E hrlich， H. Gortz， Z. Anorg. Allg. Chem. 288 (1956) 1 4 8-155. ) ( [ 1 4] P. Ehrlich ， H. Kulke，Z. Anorg. Allg. Chem. 288 (1956) 156-170. ) ( [15] B. Tanguy， M. Pezat， C. Fontenit ， J. Portier， Comp.Rendus Sec . C 280 (1975) 1019-1020. ) ( [ 1 6] H. P. Beck， A. Limmer， Z. Naturforsch.37b (1982) 574-578. ) ( [ 1 7] H. P. Beck， A. Limmer， Z. Anorg. Allg. Chem. 502 ( 1 985)1 8 5-190. ) ( [18] O . Reckeweg， F . J. D iSalvo， Z. Naturforsch. 65b (2010) 493-498. ) ( [ 1 9] O. Reckeweg， J. C.M o lstad， S. L e vy， C. Hoch， F. J. D i Salvo， Z. N a turforsch.63b(2008)513-518. ) ( [20] O . R eckeweg， F. J . DiSalvo， Z. Naturforsch. 66b(2011)21-26. ) ( [21] O. Reckeweg， J. C . Moldtstad， S. Levy， F. J. DiSalvo， Z. Naturforsch. 62b (2007) 23-27. ) ( [22] O . R eckeweg，F. J. D iSalvo，Z. Naturforsch. 66b (2011) 1 087-1091. ) ( [23]O. Reckeweg， F. J. D i Salvo， S. Wolf， Th. Schleid， z. Anorg. Allg. Chem. 64 0 (2014) 125 4 -1259. ) ( [24] N. Kunkel， D. Rudolph， A . Meijerink， S. Rommel， R . Weihrich， H. K o hlmann， Th. Schleid， Z. Anorg. Allg.Chem. 641 (2015) 1220-1224. ) ( [25] D. Rudolph， D . Enseling， T. Juistel， Th. Schleid， Z. Anorg. Allg. Chem. 643 (2017) 1525-1530. ) ( [26]H. A. Hoppe， H. Lutz， P. Morys， W. Schnick， A. Seilmeier， J. Phys. Chem. Sol.61 (2000)2001-2006. ) ( [27]C. Poesl， W. Schnick， Chem. Mater. 29(2017)3778-3784. ) ( [28] A. Meijerink， G. Blasse， J. Lumin. 43 (1989) 283-289. ) ( [29]N.K u nkel， A . Meijerink， H.Kohlmann， Phys. Chem. Chem. Phys.16 ( 2014) 4807-4813. ) ( [30] R. Hahn， N. Kunkel， C. Hein. R. Kautenburger， H. Kohlmann， RSC Ad v .， 5 (2015)9722-9728. ) ( [31] N. K unkel， A tul D . S ontakke， S. K ohaut， B . Viana， P. D o renbos， J . Phys. Chem. C 12 0 (20 1 6) 29414-29422. ) ( [32] N . Kunkel，A M e ijerink，H. K o hlmann， Inorg. Chem. 53 (2014)4800-4802. ) ( [33] N .K u nkel， H. Kohlmann， J. Phys. Chem. C 120 (2016)10 5 06-10511， ) ( [34] C. Pflug， A. Franz， H. Kohlmann， J. Solid State Chem. 25 8 (2018) 391-396. ) ( [35] G. F. Huttig， Z. Anorg. Allg. Chem. 114 (1920)，161-173. ) ( [36] F. Kubel， H . Bill， H. Hagemann， Z. Anorg. Allg. Chem. 625 ( 1999) 643-649. ) ( [37]N. Kunkel， H. Kohlmann， A. Sayede， M. Sp r ingborg， Inorg. Chem. 50 (2011) 5873-5875. ) ( [38]J. L . Sommerdijk， A. B r il， J. Lumin. 1 1 ( 1976) 363-367. ) ( [39] P. Dorenbos， J. Phys.： Condens. Matter 1 5 (2003) 2645-2665. ) ( [40] P . E. Cade， A. M S toneham， P W. Tasker， P h ys. Rev. B. 30 (1984) 4621-4639. ) ( [41] R . C . Baetzold， Phys. Rev. B 36 (1987)9182-9190. ) ( [42] R. C. Baetzold， K. S . Song ， Phys. Rev. B 48 (1993 ) 14907-14914. ) ( [43] K . S omaiah， H. Hari Babu， Phys. Stat. Sol.B 117 (1983)75-79. ) ( [44] A. J. Maeland， W. D. Lahar， Z. Phys . Chem. 179 (1993) 181-185. ) ( [45] C. Messer， J. Solid State Chem. 2(1970) 144-145. ) ( [46]H. Hagemann， H. Bill， J. M. R e y， F. K u bel， L. C a lame， D. Lo v y， J. Phys. Chem. C 119 (2015) 141-147. ) ( [47] T .Penhouet， H. Hagemann，F. Ku b el， A. Rief， J. Chem. C rystallogr. 37 (2007) 469-472. ) ( [48] N . K unkel， A. Meijerink， M. Springborg， H. Kohlmann， J. Mat. Chem. C 2 (2014) 4799-4804. ) ( [49] S. H. M. Poort， A. Meijerink， G. B l asse， J. Phys. Chem. Solids 58 (199 7 ) 1451-1456. ) ( [50] A. H . R eshak， M . Y. Sh a laginov， Y. Sa e ed， I. V. Kit y k， S. A uluck， J. Phy s . Che m . B 11 5 (2011) 2836-2841. ) ( [51] R. D. Shannon， R. C. Shannon， O. Medenbach， R. X. Fischer， J. Phys. Chem. Ref. Data 31 (2002) 931-970. ) ( [52] B. Henderson， G. F. Imbusch， O p tical S p ectroscopy of Inorganic Solids； Clarendon Pr e ss： Oxford， U.K..1989. ) ( [53]C.-K. D uan， M. F. Reid， Z. Wang， Phys. Lett. A 343 (2005) 474-480. ) ( [54] J. C. Boyer ， F. Vetrone， J. A. Capobianco， A . S peghini， M. B e ttinelli， J. Phys. Chem. B 108 ( 2 004) 20137-20143. ) ( [55]C.-K. Duan，M. F. Reid， Curr. Appl. Phys. 6(2006) 348-350. ) ( [56]D.Rudolph， Doctoral Thesis， University of Stuttgart， 2018. ) ( [57] P . Dorenbos， J. Lumin. 104 (2003)239-260. ) ( [58] C. Ronda， Luminescence， Wiley-VCH， Weinheim， 2008. ) [59]T. Kobayashi，S. Mroczkowski， J.O. Owen， L. H. Brixner， J. Lumin. 21 (1980)247-257. [60]K. Rajamohan Reddy， K. Annapurna， S. Buddhudu， Mat. Lett.28 (1996)， 489-490. ( [61]B. Tanguy， P. Merle， M. Pezat， C. Fouassier， Mater. R es. Bull. 9 (1974) 831-836. ) [62]N. Kunkel， T. Wylezich， Z. Anorg. Allg. Chem.， in print， DOI：10.1002/zaac.201800408. In our study of the optical properties of Eu2+-doped alkaline-earth metal hydride chlorides AE7H12Cl2 (AE = Ca and Sr) we observe yellow (AE = Sr) and orange-red (AE = Ca) emission. Compared to the emission energies of Eu2+ - doped fluorides, chlorides and mixed fluoride chlorides, this corresponds to a wide redshift of the Eu2+ 4f65d1–4f7 emission. We explain this observation with the strong polarizability of the hydride anion and thereforeits strong nephelauxetic effect, which shifts the 5d barycenter to lower energy. Furthermore, the redshift is even significant compared to other known hydride chlorides and hydride oxide chlorides, which is probably caused by the relatively short AE2+/Eu2+−H− distances, or it might also be caused by impurity-trapped exciton states. We have also investigated the temperature dependence of the photoluminescence lifetimes and the thermal stability.Even though the compounds are probably not ideal for phosphor application due to their low stability against air and moisture, our study underlines the large influence of the highly polarizable hydride anion on the optical properties of divalent europium and shows that Eu2+ could be used as a probe in mixed anionic system to determine the hydride content.