Trivalent bismuth luminescence is reported in three Sillen bismuth oxyhalide phases,  SrBiO2Cl, BaBiO2Cl, and BaBiO2Br. These compounds exhibit Bi 6s6-&gt; 6 s2 emission under UV and  X-ray radiation. At room temperature, BaBiO2Cl shows the most intense light emission, with  spectral and decay properties similar to those found in Bi4Ge3O12 (BGO). At low temperatures, each  phase show an increase in the photoluminescence intensities and a narrowing of the emission peaks.  In contrast to the temperature dependence of BGO, X-ray excited luminescence intensities of all  three phases remain relatively constant throughout the temperature range 10 - 295 K. This result  indicates that the Sillen phases undergo less thermal quenching than BGO. The low temperature and  room temperature radio-luminescence decay times were determined from pulsed x-ray measurements. At  room temperature, SrBiO2Cl exhibits faster decays than BGO, while, BaBiO2Cl and BaBiO2Br have  decay times similar to BGO

Bourret-Courchesne, Edith E.

Derenzo, Stephen E.

Porter-Chapman, Yetta D.

Trivalent bismuth luminescence is reported in three Sillenbismuth oxyhalide phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br. Thesecompounds exhibit Bi 6s6->6 s2 emission under UV and X-ray radiation.At room temperature, BaBiO2Cl shows the most intense light emission, withspectral and decay properties similar to those found in Bi4Ge3O12 (BGO).At low temperatures, each phase show an increase in the photoluminescenceintensities and a narrowing of the emission peaks. In contrast to thetemperature dependence of BGO, X-ray excited luminescence intensities ofall three phases remain relatively constant throughout the temperaturerange 10 - 295 K. This result indicates that the Sillen phases undergoless thermal quenching than BGO. The low temperature and room temperatureradio-luminescence decay times were determined from pulsed x-raymeasurements. At room temperature, SrBiO2Cl exhibits faster decays thanBGO, while, BaBiO2Cl and BaBiO2Br have decay times similar toBGO

Derenzo,Stephen E.

UNT Digital Library

DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California. Bi3+ Luminescence in ABiO2Cl (A = Sr, Ba) and BaBiO2Br  Yetta Porter-Chapmana, Edith Bourret-Courchesneb, Stephen E. Derenzoa,* aDepartment of Functional Imaging, Life Sciences Division  bMaterials Science Division  Ernest Orlando Lawrence Berkeley National Laboratory,  One Cyclotron Rd, Berkeley CA  94720  *Corresponding author:  (510) 486-4097 Fax: (510) 486-4768 sederenzo@lbl.gov(Stephen E. Derenzo)  Keyword: scintillator, phosphor, emission, radioluminescence, photoluminescence, bismuth   Abstract Trivalent bismuth luminescence is reported in three Sillen bismuth oxyhalide phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br. These compounds exhibit Bi 6s6p → 6s2 emission under UV and X-ray radiation. At room temperature, BaBiO2Cl shows the most intense light emission, with spectral and decay properties similar to those found in Bi4Ge3O12 (BGO).   At low temperatures, each phase show an increase in the photoluminescence intensities and a narrowing of the emission peaks.  In contrast to the temperature dependence of BGO,  X-ray excited luminescence intensities of all three phases remain relatively constant throughout the temperature range 10 – 295 K.  This result indicates that the Sillen phases undergo less thermal quenching than BGO.  The low temperature and room temperature radio-luminescence decay times were determined from pulsed x-ray measurements.  At room temperature, SrBiO2Cl exhibits faster decays than BGO, while, BaBiO2Cl and BaBiO2Br have decay times similar to BGO.   1.  Introduction  Trivalent bismuth cations in inorganic compounds or hosts commonly exhibit interesting luminescence properties originating from the excitation and relaxation of its 6s2 inert lone pair electrons[1-7].  In this regard, an investigation of compounds containing Bi3+ has great potential towards the discovery of new intrinsically luminescent materials. We present three bismuth oxyhalide phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br, that exhibit such Bi3+ luminescence. In general, the Sillen bismuth oxyhalide phases (ABi3+O2X, where A = divalent cation and X = Cl, Br, I) have garnered significant attention with interests centered around their catalytic properties[8, 9] and interesting crystal structures[10-15].  This work introduces photo- and radio-luminescence properties of these three members of the Sillen bismuth oxyhalide family. Their luminescence properties are compared to Bi4Ge3O12 (BGO), an important material with electro-optic[16, 17], nonlinear optic[18], and scintillation[2, 7] capabilities.  The preparation, photoluminescence, and time resolved x-ray luminescence of these compounds are detailed in this report.    2.   Experimental  The oxychlorides, SrBiO2Cl and BaBiO2Cl, were synthesized from 1:1 molar ratios of the corresponding alkali earth carbonate, SrCO3 (99.999 %, Strem) or BaCO3  (99.8 %, Alfa Aesar) and BiOCl (99.999 %, Alfa Aesar).  BaBiO2Br was synthesized from 3:1:1 molar ratio of BaCO3, Bi2O3 (99.999 %, Strem), and BiBr3 (98+ %, Strem). For each sample, the reactant powders were thoroughly ground together into a homogeneous mixture using a mortar and pestle, transferred to an alumina boat, and subsequently heated in air at 800 °C for 10 hours in a tube furnace.  White (SrBiO2Cl and BaBiO2Cl) or light yellow (BaBiO2Br) polycrystalline powders were obtained from these reactions.    Crystal phase identifications were performed on a Siemens D500 powder X-ray diffractometer using 1.540510 Å Cu Kα radiation, a range of 10 – 50° (2θ), a scan interval of 0.09° /step, and a step rate of 1° /sec. All luminescence measurements were conducted on samples consisting of 5 – 20 µm sized particles contained in quartz cuvettes. Low temperature (10 – 250 K) and room temperature (295 K) photo- and radio-luminescence spectra were measured for each Sillen phase, along with a standard Bi4Ge3O12 (BGO) sample.  Photoluminescence excitation and emission spectra were collected on a Horiba Fluorolog 3 fluorescence spectrometer within the spectral range of  250 nm – 800 nm using excitation and emission slit widths of 3 nm.  Each excitation spectrum was taken while observing emission at the predetermined emission wavelength maxima, and likewise, the emission spectra was taken while exciting at the sample’s excitation wavelength maxima. Radio-luminescence decay measurements were performed utilizing an in-house pulsed X-ray system that produces 80 ps (fwhm) pulses of X-rays having a mean energy of 18 keV.  Fluorescent photons from the sample are detected by a microchannel phototube with 35 ps (fwhm) response [19]. The luminescence decay times were determined by fitting the data to multiexponential decay curves [19]. An Advanced Research Systems, Inc. ARS2-A closed-cycle helium refrigerator was used for the low temperature measurements.    3.   Results and Discussion 3.1  Photoluminescence Te energy levels of interest for luminescent ns2 cations (e.g., Pb2+, Sn2+, and Bi3+) are the ground state, 1S0,  and the four excited states (in order of increasing energy), 3P0,  3P1,  3P2, and 1P1  (see Fig. 1).  Transitions between 1S0  and  3P0,  3P1, or  3P2 are spin forbidden, however, the 3P 1 level undergoes mixing with 1P1 by spin-orbit coupling, allowing the 1S0 ↔ 3P1 transitions that are frequently observed in photoluminescence measurements[1, 3, 4, 6, 7, 20].  The 1S0 → 1P1  transition is also observed in some materials.  In the case of Bi3+, broad emission peaks, whose number and positions depend on the crystal field around the cation, and large Stokes shifts are commonly observed [1, 3, 4, 7, 20, 21].  All three Sillen phases are isostructural, crystallizing in the orthorhombic space group Cmcm [13].  Each bismuth cation has  C4v site symmetry with coordination to eight substituents (4O + 4Cl) in a square antiprismatic arrangement.  Excitation and emission spectra of each Sillen phase is presented in Fig. 2.  A broad, undefined excitation peak and one emission peak are observed for each Sillen phase and BGO.  As reported in Table 1, at 295 K, the excitation peak maxima and emission peak maxima of SrBiO2Cl, BaBiO2Cl, and BaBiO2Br occur at 280 and 430; 300 and 490; and 305 and 500 nm, respectively.  The Stokes shifts of SrBiO2Cl, BaBiO2Br, and BaBiO2Cl are calculated to be 12,500, 12,800, and 12,900 cm-1, are as expected from the heterotypic bonding of the bismuth cations in these phases. The strontium compound exhibits slightly bluer excitation and emission bands owing to the nephelauxetic effect [1, 22].  In this case, the Sr - O(X) bonds are more ionic than the Ba – O(X) bonds contributing to the shorter excitation wavelength for SrBiO2Cl. Following this trend, the lower electronegativity of bromine correlates to the smaller Stokes shift found for BaBiO2Br in comparison to BaBiO2Cl. For all three Sillen phases, the excitation and emission bands are assigned to transitions between the 1S0 ground state and the 3P1 excited state.  The intensities of the photoemission peaks of the Sillen phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br, are shown in Fig. 3 for temperature range 10 K - 295 K. At low temperatures, the emission peaks narrow and the emission intensities increase for Bi4Ge3O12 (BGO) [2, 5, 7] and for the three Sillen phases.  From 10 – 77 K the emission intensities are relatively constant.  As the temperature increases from 77 K to 295 K, the emission intensities decrease by 29 %, 73 %, and 88 % for SrBiO2Cl, BaBiO2Br, and BaBiO2Cl, respectively.  In BaBiO2Cl and BaBiO2Br, the highest photoluminescence intensities occur at 77 K, while the largest intensity for SrBiO2Cl occurred at 20 K.  At temperatures < 295 K, the emission wavelengths shift to 545 nm for BaBiO2Cl and 550 nm for BaBiO2Br, whereas in SrBiO2Cl, the emission maxima stays the same.  This nonshift indicates that the photoemissive states of SrBiO2Cl are less thermally influenced relative to the other two Sillen phases.  This observation was further confirmed by the stability of the emission intensities with variation of temperature for SrBiO2Cl, (see Fig. 3).  Of the Sillen phases investigated, BaBiO2Cl exhibits the most intense photoluminescence, 1.73 times that of BGO, at room temperature, however, as described below, it does not translate into high radioluminosity (see Table 1).    3.2  X-ray Luminescence  Pulsed x-ray measurements were performed on polycrystalline samples of the three Sillen phases and BGO.  The room temperature x-ray excited luminosities of SrBiO2Cl, BaBiO2Br, and BaBiO2Cl are found to be 24 %, 27 %, and 81 % of the luminescence found for BGO (Table 1).  As shown in Fig. 4, the two barium bismuth oxyhalides exhibit consistent luminosities throughout the temperature range 10 K - 250 K.  SrBiO2Cl behaves in a manner similar to BGO at  temperatures >100 K, where nonradiative thermal quenching processes compete with radiative transitions.  However, the x-ray excited emissive states of BaBiO2Cl and BaBiO2Br are temperature dependent only at temperatures > 250 K, where the luminosities decrease slightly.   The time resolved decay measurements yield multiexponential decays for all three Sillen phases (see Fig. 5). At low temperatures, the majority of the X-ray excited emission have decay times  > 1000 ns.  As the temperature increases, the decay time components for all three Sillen compounds decrease, as shown for BaBiO2Cl in Fig. 6.  A complete listing of the three largest decay components and their fractions for SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and BGO measured at various temperatures can be found in Appendix A.  The strontium compound, SrBiO2Cl, exhibits relatively fast decay times of 50, 200, and 300 ns at 295 K for its most significant decay components when compared to the other two Sillen compounds and BGO. The shorter decay times observed at higher temperatures are attributed to nonradiative quenching commonly found in Bi3+-activated materials.  This is usually accompanied by significantly lower luminosities at high temperatures, however, the radio-luminescence observed in BaBiO2Cl and BaBiO2Br are not as temperature dependent in comparison to the luminosities found in SrBiO2Cl and BGO.   5.   Conclusion  Three Sillen bismuth oxyhalides, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br were found to exhibit photo- and radio-luminescence.  Their luminosities originate from the 3P1→1S0 emission of the Bi3+ luminescent ion.  At low temperatures, the radio-luminescence decay times increase, the photo-emission wavelengths shift to lower energy (in the case of the barium phases only), and the photo-emission bands narrow. These features are explained by the decrease in thermal population of the excited states at low temperatures.  The three Sillen compounds have been characterized for their optical and scintillation properties and compared to Bi4Ge3O12 (BGO).   Acknowledgements.  The authors would like to thank Marvin Weber for his invaluable advice towards the work presented in this manuscript. This work was supported in part by the Director, Office of Science, Office of Biological and Environmental Research, Medical Science  Division of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and in part by Public Health Service grant number R01EB00339 awarded by the National Institute of Biomedical Imaging and Bioengineering, Department of Health and Human Services.   Appendix A.  Radio-luminescence decay constants and fractional contributions at various temperatures for SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and Bi4Ge3O12. Temperature (K) SrBiO2Cl BaBiO2Cl BaBiO2Br Bi4Ge3O12 τ Fraction τ Fraction τ Fraction τ Fraction100 6% 100 4% 100 6% 900 21% 800 39% 800 28% 800 38% 5950 45%10 3500 50% 4200 59% 3000 51% 6000 33% 100 6% 100 4% 150 3% 100 2% 800 39% 800 27% 700 28% 950 20%25 3800 52% 4200 61% 3750 62% 6150 78% 100 6% 150 7% 150 3% 100 2% 800 39% 900 39% 950 33% 900 18%77 3500 50% 3600 50% 5800 48% 6150 80% 100 8% 150 10% 150 9% 900 21% 750 38% 800 43% 800 40% 5300 57%100 2850 50% 2450 43% 2900 48% 5350 19% 150 8% 150 10% 150 9% 100 2% 700 41% 650 42% 600 40% 850 24%150 2400 45% 1650 42% 1700 46% 3650 71% 200 13% 200 18% 150 15% 100 4% 750 55% 700 62% 650 55% 800 33%200 1900 26% 1600 14% 1400 24% 2400 61% 150 15% 150 11% 100 11% 200 8% 300 20% 300 19% 300 23% 800 70%250 650 48% 700 56% 600 54% 1500 16% 50 28% 100 22% 100 21% 100 12% 200 38% 300 41% 300 54% 300 79%295 300 14% 600 23% 700 12% 1000 4%    References [1] G. Blasse, A. Bril, J. Chem. Phys. 48 (1968) 217.  [2] E. Dieguez, L. Arizmendi, J. M. Cabrera, J. Phys. C: Solid State Phys. 18 (1985) 4777.  [3] B. Jacquier, G. Boulon, G. Sallavuard, F. Gaume-Mahn, J. Solid State Chem. 4 (1972) 374.  [4] C.-H. Kim, C.-H. Pyun, H. Choi, S.-J. Kim, Bull. Korean Chem. Soc. 20 (1999) 337.  [5] R. Moncorge, B. Jacquier, G. Boulon, J. Luminescence 14 (1976) 337.  [6] S. Shinonoya, W. M. Yen, The Phosphor Handbook, CRC Press, Boca Raton, FL, (2000) 141.  [7] M. J. Weber, R. R. Monchamp, J. Appl. Phys. 44 (1973) 5495.  [8] R. Burch, S. Chalker, R. Loader, J. M. Thomas, W. Ueda, Appl. Catal. 82 (1992) 77. [9] J. M. Thomas, W. Ueda, J. Williams, K. D. M. Harris, J. Chem. Soc. Faraday Discussions 87 (1989) 33. [10] D. O. Charkin, P. S. Berdonosov, V. A. Dolgikh, P. Lightfoot, J. Solid State Chem. 175 (2003) 316. [11] V. A. Dolgikh, L. N. Kholodkovskaya, Russ. J. Inorg. Chem. 37 (1992) 488. [12] S. M. Fray, C. J. Milne, P. Lightfoot, J. Solid State Chem. 129 (1997) 115.  [13] M. A. Kennard, J. Darriet, J. Grannec, A. Tressaud, J. Solid State Chem. 117 (1995) 201. [14] L. G. Sillen, Z. Anorg. Allgem. Chem. 242 (1939) 41. [15] L. G. Sillen, Naturwissenschften 22 (1942) 318. [16] R. Nitsche, J. Appl. Phys. 36 (1965) 2358.  [17] P. A. Williams, A. H. Rose, K. S. Lee, D. C. Conrad, G. W. Day, P. D. Hale, Appl. Opt. 35 (1996) 3562. [18] S. K. Kurtz, T. T. Perry, J. Appl. Phys. 39 (1968) 3798.  [19] S. E. Derenzo, M. J. Weber, W. W. Moses, C. Dujardin, IEEE Trans. Nucl. Sci. NS-47 (2000) 860. [20] P. A. Rodnyi, Physical Processes in Inorganic Scintillators, CRC Press, Boca Raton, FL, (1997) 142.  [21] W. C. De Gruijter, J. Solid State Chem. 6 (1973) 151.  [22] J. A. Duffy, Bonding, energy levels, and bands in inorganic solids, Wiley, Essex, Eng, (1990).   Figure Captions  Fig. 1.  Sketch of Bi3+ energy levels and possible electronic transitions.  Fig. 2.  Room temperature excitation and emission spectra of  SrBiO2Cl, BaBiO2Cl (and BaBiO2Br, and Bi4Ge3O12 (BGO).  Intensities normalized to the emission peak maxima of BGO. Note: λ - emission and excitation wavelengths used in measurements.  Fig. 3.  Temperature dependence of the photoluminescence of SrBiO2Cl, BaBiO2Cl and BaBiO2Br. (Excitation wavelengths identical to those used in Fig. 2)  Fig. 4. Temperature dependence of radio-luminescence of SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and Bi4Ge3O12.   Fig.5. Radio-luminescence decay curves of SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and Bi4Ge3O12 at room temperature.   Fig.6. Temperature dependence of the multiexponential decay of BaBiO2Cl.       Table 1.  Densities, relative radioluminescence intensities, and emission wavelengths of ABiO2Cl (A = Sr, Ba), BaBiO2Br, and Bi4Ge3O12 at room temperature.  Compound Density Relative Radio-luminescence Emission maxima (nm) SrBiO2Cl 6.10 0.24 430 BaBiO2Cl 6.36 0.81 490 BaBiO2Br 6.71 0.27 500 Bi4Ge3O12 7.1 1.00 460      Energy1P13P13P23P01S0 Fig. 1  00.511.52300 350 400 450 500 550 600 650 700BaBiO2ClExcitationEmissionRelative Intensity00.050.10.15300 350 400 450 500 550 600 650 700SrBiO2ClExcitationEmissionRelative Intensity00.050.10.150.20.250.30.35300 350 400 450 500 550 600 650 700BaBiO2BrExcitationEmissionWavelength (nm)Relative Intensity00.20.40.60.811.2300 350 400 450 500 550 600 650 700BGOExcitationEmissionWavelength (nm)Relative IntensityΛ (nm)500300 Λ (nm)430280 Λ (nm)460270 Λ (nm)490300 Relative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityFig. 2.       05 1051 1061.5 1062 1060 50 100 150 200 250 300SrBiO2ClBaBiO2ClBaBiO2BrTemperature (K)Intensity (a.u.)Intensity (a.u.)           Fig. 3.             010002000300040005000600070000 50 100 150 200 250 300SrBiO2ClBaBiO2ClBaBiO2BrBGOTemperature (K)Relative LuminosityRelative LuminosityRelative Luminosity Fig. 4.         Relative LuminosityBGOSrBiO2ClBaBiO2Cl & BaBiO2BrTime (ns)11010010001040 500 1000 1500 2000 2500 3000Relative Luminosity  Fig. 5.      Relative LuminosityTime (ns)10 – 77 K100 – 250 K295 K0.111010010000 1000 2000 3000 4000 5000 6000Relative Luminosity Fig.6.      

Bi3+ Luminescence in ABiO2Cl (A = Sr, Ba) and BaBiO2Br

eScholarship - University of California

Lawrence Berkeley National LaboratoryLawrence Berkeley National LaboratoryTitleBi3+ Luminescence in ABiO2Cl (A = Sr, Ba) and BaBiO2BrPermalinkhttps://escholarship.org/uc/item/4nb403g5AuthorsPorter-Chapman, Yetta D.Bourret-Courchesne, Edith E.Derenzo, Stephen E.Publication Date2007-01-18 Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaDISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California. Bi3+ Luminescence in ABiO2Cl (A = Sr, Ba) and BaBiO2Br  Yetta Porter-Chapmana, Edith Bourret-Courchesneb, Stephen E. Derenzoa,* aDepartment of Functional Imaging, Life Sciences Division  bMaterials Science Division  Ernest Orlando Lawrence Berkeley National Laboratory,  One Cyclotron Rd, Berkeley CA  94720  *Corresponding author:  (510) 486-4097 Fax: (510) 486-4768 sederenzo@lbl.gov(Stephen E. Derenzo)  Keyword: scintillator, phosphor, emission, radioluminescence, photoluminescence, bismuth   Abstract Trivalent bismuth luminescence is reported in three Sillen bismuth oxyhalide phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br. These compounds exhibit Bi 6s6p → 6s2 emission under UV and X-ray radiation. At room temperature, BaBiO2Cl shows the most intense light emission, with spectral and decay properties similar to those found in Bi4Ge3O12 (BGO).   At low temperatures, each phase show an increase in the photoluminescence intensities and a narrowing of the emission peaks.  In contrast to the temperature dependence of BGO,  X-ray excited luminescence intensities of all three phases remain relatively constant throughout the temperature range 10 – 295 K.  This result indicates that the Sillen phases undergo less thermal quenching than BGO.  The low temperature and room temperature radio-luminescence decay times were determined from pulsed x-ray measurements.  At room temperature, SrBiO2Cl exhibits faster decays than BGO, while, BaBiO2Cl and BaBiO2Br have decay times similar to BGO.   1.  Introduction  Trivalent bismuth cations in inorganic compounds or hosts commonly exhibit interesting luminescence properties originating from the excitation and relaxation of its 6s2 inert lone pair electrons[1-7].  In this regard, an investigation of compounds containing Bi3+ has great potential towards the discovery of new intrinsically luminescent materials. We present three bismuth oxyhalide phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br, that exhibit such Bi3+ luminescence. In general, the Sillen bismuth oxyhalide phases (ABi3+O2X, where A = divalent cation and X = Cl, Br, I) have garnered significant attention with interests centered around their catalytic properties[8, 9] and interesting crystal structures[10-15].  This work introduces photo- and radio-luminescence properties of these three members of the Sillen bismuth oxyhalide family. Their luminescence properties are compared to Bi4Ge3O12 (BGO), an important material with electro-optic[16, 17], nonlinear optic[18], and scintillation[2, 7] capabilities.  The preparation, photoluminescence, and time resolved x-ray luminescence of these compounds are detailed in this report.    2.   Experimental  The oxychlorides, SrBiO2Cl and BaBiO2Cl, were synthesized from 1:1 molar ratios of the corresponding alkali earth carbonate, SrCO3 (99.999 %, Strem) or BaCO3  (99.8 %, Alfa Aesar) and BiOCl (99.999 %, Alfa Aesar).  BaBiO2Br was synthesized from 3:1:1 molar ratio of BaCO3, Bi2O3 (99.999 %, Strem), and BiBr3 (98+ %, Strem). For each sample, the reactant powders were thoroughly ground together into a homogeneous mixture using a mortar and pestle, transferred to an alumina boat, and subsequently heated in air at 800 °C for 10 hours in a tube furnace.  White (SrBiO2Cl and BaBiO2Cl) or light yellow (BaBiO2Br) polycrystalline powders were obtained from these reactions.    Crystal phase identifications were performed on a Siemens D500 powder X-ray diffractometer using 1.540510 Å Cu Kα radiation, a range of 10 – 50° (2θ), a scan interval of 0.09° /step, and a step rate of 1° /sec. All luminescence measurements were conducted on samples consisting of 5 – 20 µm sized particles contained in quartz cuvettes. Low temperature (10 – 250 K) and room temperature (295 K) photo- and radio-luminescence spectra were measured for each Sillen phase, along with a standard Bi4Ge3O12 (BGO) sample.  Photoluminescence excitation and emission spectra were collected on a Horiba Fluorolog 3 fluorescence spectrometer within the spectral range of  250 nm – 800 nm using excitation and emission slit widths of 3 nm.  Each excitation spectrum was taken while observing emission at the predetermined emission wavelength maxima, and likewise, the emission spectra was taken while exciting at the sample’s excitation wavelength maxima. Radio-luminescence decay measurements were performed utilizing an in-house pulsed X-ray system that produces 80 ps (fwhm) pulses of X-rays having a mean energy of 18 keV.  Fluorescent photons from the sample are detected by a microchannel phototube with 35 ps (fwhm) response [19]. The luminescence decay times were determined by fitting the data to multiexponential decay curves [19]. An Advanced Research Systems, Inc. ARS2-A closed-cycle helium refrigerator was used for the low temperature measurements.    3.   Results and Discussion 3.1  Photoluminescence Te energy levels of interest for luminescent ns2 cations (e.g., Pb2+, Sn2+, and Bi3+) are the ground state, 1S0,  and the four excited states (in order of increasing energy), 3P0,  3P1,  3P2, and 1P1  (see Fig. 1).  Transitions between 1S0  and  3P0,  3P1, or  3P2 are spin forbidden, however, the 3P 1 level undergoes mixing with 1P1 by spin-orbit coupling, allowing the 1S0 ↔ 3P1 transitions that are frequently observed in photoluminescence measurements[1, 3, 4, 6, 7, 20].  The 1S0 → 1P1  transition is also observed in some materials.  In the case of Bi3+, broad emission peaks, whose number and positions depend on the crystal field around the cation, and large Stokes shifts are commonly observed [1, 3, 4, 7, 20, 21].  All three Sillen phases are isostructural, crystallizing in the orthorhombic space group Cmcm [13].  Each bismuth cation has  C4v site symmetry with coordination to eight substituents (4O + 4Cl) in a square antiprismatic arrangement.  Excitation and emission spectra of each Sillen phase is presented in Fig. 2.  A broad, undefined excitation peak and one emission peak are observed for each Sillen phase and BGO.  As reported in Table 1, at 295 K, the excitation peak maxima and emission peak maxima of SrBiO2Cl, BaBiO2Cl, and BaBiO2Br occur at 280 and 430; 300 and 490; and 305 and 500 nm, respectively.  The Stokes shifts of SrBiO2Cl, BaBiO2Br, and BaBiO2Cl are calculated to be 12,500, 12,800, and 12,900 cm-1, are as expected from the heterotypic bonding of the bismuth cations in these phases. The strontium compound exhibits slightly bluer excitation and emission bands owing to the nephelauxetic effect [1, 22].  In this case, the Sr - O(X) bonds are more ionic than the Ba – O(X) bonds contributing to the shorter excitation wavelength for SrBiO2Cl. Following this trend, the lower electronegativity of bromine correlates to the smaller Stokes shift found for BaBiO2Br in comparison to BaBiO2Cl. For all three Sillen phases, the excitation and emission bands are assigned to transitions between the 1S0 ground state and the 3P1 excited state.  The intensities of the photoemission peaks of the Sillen phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br, are shown in Fig. 3 for temperature range 10 K - 295 K. At low temperatures, the emission peaks narrow and the emission intensities increase for Bi4Ge3O12 (BGO) [2, 5, 7] and for the three Sillen phases.  From 10 – 77 K the emission intensities are relatively constant.  As the temperature increases from 77 K to 295 K, the emission intensities decrease by 29 %, 73 %, and 88 % for SrBiO2Cl, BaBiO2Br, and BaBiO2Cl, respectively.  In BaBiO2Cl and BaBiO2Br, the highest photoluminescence intensities occur at 77 K, while the largest intensity for SrBiO2Cl occurred at 20 K.  At temperatures < 295 K, the emission wavelengths shift to 545 nm for BaBiO2Cl and 550 nm for BaBiO2Br, whereas in SrBiO2Cl, the emission maxima stays the same.  This nonshift indicates that the photoemissive states of SrBiO2Cl are less thermally influenced relative to the other two Sillen phases.  This observation was further confirmed by the stability of the emission intensities with variation of temperature for SrBiO2Cl, (see Fig. 3).  Of the Sillen phases investigated, BaBiO2Cl exhibits the most intense photoluminescence, 1.73 times that of BGO, at room temperature, however, as described below, it does not translate into high radioluminosity (see Table 1).    3.2  X-ray Luminescence  Pulsed x-ray measurements were performed on polycrystalline samples of the three Sillen phases and BGO.  The room temperature x-ray excited luminosities of SrBiO2Cl, BaBiO2Br, and BaBiO2Cl are found to be 24 %, 27 %, and 81 % of the luminescence found for BGO (Table 1).  As shown in Fig. 4, the two barium bismuth oxyhalides exhibit consistent luminosities throughout the temperature range 10 K - 250 K.  SrBiO2Cl behaves in a manner similar to BGO at  temperatures >100 K, where nonradiative thermal quenching processes compete with radiative transitions.  However, the x-ray excited emissive states of BaBiO2Cl and BaBiO2Br are temperature dependent only at temperatures > 250 K, where the luminosities decrease slightly.   The time resolved decay measurements yield multiexponential decays for all three Sillen phases (see Fig. 5). At low temperatures, the majority of the X-ray excited emission have decay times  > 1000 ns.  As the temperature increases, the decay time components for all three Sillen compounds decrease, as shown for BaBiO2Cl in Fig. 6.  A complete listing of the three largest decay components and their fractions for SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and BGO measured at various temperatures can be found in Appendix A.  The strontium compound, SrBiO2Cl, exhibits relatively fast decay times of 50, 200, and 300 ns at 295 K for its most significant decay components when compared to the other two Sillen compounds and BGO. The shorter decay times observed at higher temperatures are attributed to nonradiative quenching commonly found in Bi3+-activated materials.  This is usually accompanied by significantly lower luminosities at high temperatures, however, the radio-luminescence observed in BaBiO2Cl and BaBiO2Br are not as temperature dependent in comparison to the luminosities found in SrBiO2Cl and BGO.   5.   Conclusion  Three Sillen bismuth oxyhalides, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br were found to exhibit photo- and radio-luminescence.  Their luminosities originate from the 3P1→1S0 emission of the Bi3+ luminescent ion.  At low temperatures, the radio-luminescence decay times increase, the photo-emission wavelengths shift to lower energy (in the case of the barium phases only), and the photo-emission bands narrow. These features are explained by the decrease in thermal population of the excited states at low temperatures.  The three Sillen compounds have been characterized for their optical and scintillation properties and compared to Bi4Ge3O12 (BGO).   Acknowledgements.  The authors would like to thank Marvin Weber for his invaluable advice towards the work presented in this manuscript. This work was supported in part by the Director, Office of Science, Office of Biological and Environmental Research, Medical Science  Division of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and in part by Public Health Service grant number R01EB00339 awarded by the National Institute of Biomedical Imaging and Bioengineering, Department of Health and Human Services.   Appendix A.  Radio-luminescence decay constants and fractional contributions at various temperatures for SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and Bi4Ge3O12. Temperature (K) SrBiO2Cl BaBiO2Cl BaBiO2Br Bi4Ge3O12 τ Fraction τ Fraction τ Fraction τ Fraction100 6% 100 4% 100 6% 900 21% 800 39% 800 28% 800 38% 5950 45%10 3500 50% 4200 59% 3000 51% 6000 33% 100 6% 100 4% 150 3% 100 2% 800 39% 800 27% 700 28% 950 20%25 3800 52% 4200 61% 3750 62% 6150 78% 100 6% 150 7% 150 3% 100 2% 800 39% 900 39% 950 33% 900 18%77 3500 50% 3600 50% 5800 48% 6150 80% 100 8% 150 10% 150 9% 900 21% 750 38% 800 43% 800 40% 5300 57%100 2850 50% 2450 43% 2900 48% 5350 19% 150 8% 150 10% 150 9% 100 2% 700 41% 650 42% 600 40% 850 24%150 2400 45% 1650 42% 1700 46% 3650 71% 200 13% 200 18% 150 15% 100 4% 750 55% 700 62% 650 55% 800 33%200 1900 26% 1600 14% 1400 24% 2400 61% 150 15% 150 11% 100 11% 200 8% 300 20% 300 19% 300 23% 800 70%250 650 48% 700 56% 600 54% 1500 16% 50 28% 100 22% 100 21% 100 12% 200 38% 300 41% 300 54% 300 79%295 300 14% 600 23% 700 12% 1000 4%    References [1] G. Blasse, A. Bril, J. Chem. Phys. 48 (1968) 217.  [2] E. Dieguez, L. Arizmendi, J. M. Cabrera, J. Phys. C: Solid State Phys. 18 (1985) 4777.  [3] B. Jacquier, G. Boulon, G. Sallavuard, F. Gaume-Mahn, J. Solid State Chem. 4 (1972) 374.  [4] C.-H. Kim, C.-H. Pyun, H. Choi, S.-J. Kim, Bull. Korean Chem. Soc. 20 (1999) 337.  [5] R. Moncorge, B. Jacquier, G. Boulon, J. Luminescence 14 (1976) 337.  [6] S. Shinonoya, W. M. Yen, The Phosphor Handbook, CRC Press, Boca Raton, FL, (2000) 141.  [7] M. J. Weber, R. R. Monchamp, J. Appl. Phys. 44 (1973) 5495.  [8] R. Burch, S. Chalker, R. Loader, J. M. Thomas, W. Ueda, Appl. Catal. 82 (1992) 77. [9] J. M. Thomas, W. Ueda, J. Williams, K. D. M. Harris, J. Chem. Soc. Faraday Discussions 87 (1989) 33. [10] D. O. Charkin, P. S. Berdonosov, V. A. Dolgikh, P. Lightfoot, J. Solid State Chem. 175 (2003) 316. [11] V. A. Dolgikh, L. N. Kholodkovskaya, Russ. J. Inorg. Chem. 37 (1992) 488. [12] S. M. Fray, C. J. Milne, P. Lightfoot, J. Solid State Chem. 129 (1997) 115.  [13] M. A. Kennard, J. Darriet, J. Grannec, A. Tressaud, J. Solid State Chem. 117 (1995) 201. [14] L. G. Sillen, Z. Anorg. Allgem. Chem. 242 (1939) 41. [15] L. G. Sillen, Naturwissenschften 22 (1942) 318. [16] R. Nitsche, J. Appl. Phys. 36 (1965) 2358.  [17] P. A. Williams, A. H. Rose, K. S. Lee, D. C. Conrad, G. W. Day, P. D. Hale, Appl. Opt. 35 (1996) 3562. [18] S. K. Kurtz, T. T. Perry, J. Appl. Phys. 39 (1968) 3798.  [19] S. E. Derenzo, M. J. Weber, W. W. Moses, C. Dujardin, IEEE Trans. Nucl. Sci. NS-47 (2000) 860. [20] P. A. Rodnyi, Physical Processes in Inorganic Scintillators, CRC Press, Boca Raton, FL, (1997) 142.  [21] W. C. De Gruijter, J. Solid State Chem. 6 (1973) 151.  [22] J. A. Duffy, Bonding, energy levels, and bands in inorganic solids, Wiley, Essex, Eng, (1990).   Figure Captions  Fig. 1.  Sketch of Bi3+ energy levels and possible electronic transitions.  Fig. 2.  Room temperature excitation and emission spectra of  SrBiO2Cl, BaBiO2Cl (and BaBiO2Br, and Bi4Ge3O12 (BGO).  Intensities normalized to the emission peak maxima of BGO. Note: λ - emission and excitation wavelengths used in measurements.  Fig. 3.  Temperature dependence of the photoluminescence of SrBiO2Cl, BaBiO2Cl and BaBiO2Br. (Excitation wavelengths identical to those used in Fig. 2)  Fig. 4. Temperature dependence of radio-luminescence of SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and Bi4Ge3O12.   Fig.5. Radio-luminescence decay curves of SrBiO2Cl, BaBiO2Cl, BaBiO2Br, and Bi4Ge3O12 at room temperature.   Fig.6. Temperature dependence of the multiexponential decay of BaBiO2Cl.       Table 1.  Densities, relative radioluminescence intensities, and emission wavelengths of ABiO2Cl (A = Sr, Ba), BaBiO2Br, and Bi4Ge3O12 at room temperature.  Compound Density Relative Radio-luminescence Emission maxima (nm) SrBiO2Cl 6.10 0.24 430 BaBiO2Cl 6.36 0.81 490 BaBiO2Br 6.71 0.27 500 Bi4Ge3O12 7.1 1.00 460      Energy1P13P13P23P01S0 Fig. 1  00.511.52300 350 400 450 500 550 600 650 700BaBiO2ClExcitationEmissionRelative Intensity00.050.10.15300 350 400 450 500 550 600 650 700SrBiO2ClExcitationEmissionRelative Intensity00.050.10.150.20.250.30.35300 350 400 450 500 550 600 650 700BaBiO2BrExcitationEmissionWavelength (nm)Relative Intensity00.20.40.60.811.2300 350 400 450 500 550 600 650 700BGOExcitationEmissionWavelength (nm)Relative IntensityΛ (nm)500300 Λ (nm)430280 Λ (nm)460270 Λ (nm)490300 Relative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityRelative IntensityFig. 2.       05 1051 1061.5 1062 1060 50 100 150 200 250 300SrBiO2ClBaBiO2ClBaBiO2BrTemperature (K)Intensity (a.u.)Intensity (a.u.)           Fig. 3.             010002000300040005000600070000 50 100 150 200 250 300SrBiO2ClBaBiO2ClBaBiO2BrBGOTemperature (K)Relative LuminosityRelative LuminosityRelative Luminosity Fig. 4.         Relative LuminosityBGOSrBiO2ClBaBiO2Cl & BaBiO2BrTime (ns)11010010001040 500 1000 1500 2000 2500 3000Relative Luminosity  Fig. 5.      Relative LuminosityTime (ns)10 – 77 K100 – 250 K295 K0.111010010000 1000 2000 3000 4000 5000 6000Relative Luminosity Fig.6.      

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Bi3+ Luminescence in ABiO2Cl (A = Sr, Ba) and BaBiO2Br

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