We report the long-lasting bluish-green phosphorescence for X-ray or cathode ray tubes in the phosphors with compositions of either Ba2SiO4:0.01Eu2+–xSi3N4 (x=0–1) or 2BaCO3–ySi3N4:0.01Eu2+(y=1/6–1) synthesized by a solid-state reaction. By tuning the Si3N4content, the phosphorescence may originate from Eu2+ in BaSi2O2N2(peaking at 490 nm), Ba2SiO4 (505 nm), and Ba3SiO5 (590 nm) phases. The strong phosphorescence of the Ba2SiO4:Eu2+ phase in 2BaCO3–ySi3N4:0.01Eu2+ is attributed to N substitution for O to generate a shallow trap. In Ba2SiO4:0.01Eu2+–xSi3N4 , however, N prefers reacting with Ba2SiO4 to form BaSi2O2N2 , thereby exhibiting a strong phosphorescence of the BaSi2O2N2:Eu2+ phase but a weak phosphorescence of the Ba2SiO4:Eu2+ phase

Hao, Zhendong

Luo, Yongshi

Ren, Xinguang

Wang, Meiyuan

Wang, Xiao-Jun

Zhang, Jiahua

Zhang, Xia

Zhao, Haifeng

English

Georgia Southern University: Digital Commons@Georgia Southern

Georgia Southern University Digital Commons@Georgia Southern Physics and Astronomy Faculty Publications Physics and Astronomy, Department of 2010 Long-Lasting Phosphorescence in BaSi2O2N2:Eu2+ and Ba2SiO4:Eu2+ Phases for X-Ray and Cathode Ray Tubes Meiyuan Wang Chinese Academy of Sciences Xia Zhang Chinese Academy of Sciences Zhendong Hao Chinese Academy of Sciences Xinguang Ren Chinese Academy of Sciences Yongshi Luo Chinese Academy of Sciences See next page for additional authors Follow this and additional works at: https://digitalcommons.georgiasouthern.edu/physics-facpubs  Part of the Physics Commons Recommended Citation Wang, Meiyuan, Xia Zhang, Zhendong Hao, Xinguang Ren, Yongshi Luo, Haifeng Zhao, Xiao-Jun Wang, Jiahua Zhang. 2010. "Long-Lasting Phosphorescence in BaSi2O2N2:Eu2+ and Ba2SiO4:Eu2+ Phases for X-Ray and Cathode Ray Tubes." Journal of the Electrochemical Society, 157 (2): H178-H181. doi: 10.1149/1.3267513 https://digitalcommons.georgiasouthern.edu/physics-facpubs/71 This article is brought to you for free and open access by the Physics and Astronomy, Department of at Digital Commons@Georgia Southern. It has been accepted for inclusion in Physics and Astronomy Faculty Publications by an authorized administrator of Digital Commons@Georgia Southern. For more information, please contact digitalcommons@georgiasouthern.edu. Authors Meiyuan Wang, Xia Zhang, Zhendong Hao, Xinguang Ren, Yongshi Luo, Haifeng Zhao, Xiao-Jun Wang, and Jiahua Zhang This article is available at Digital Commons@Georgia Southern: https://digitalcommons.georgiasouthern.edu/physics-facpubs/71 Long-Lasting Phosphorescence in BaSi2O2N2:Eu2+ andBa2SiO4:Eu2+ Phases for X-Ray and Cathode Ray TubesMeiyuan Wang,a,b Xia Zhang,a Zhendong Hao,a Xinguang Ren,aYongshi Luo,a Haifeng Zhao,a Xiaojun Wang,c and Jiahua Zhanga,zaKey Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics,Chinese Academy of Sciences, Changchun 130033, ChinabGraduate School of Chinese Academy of Sciences, Beijing 100039, ChinacDepartment of Physics, Georgia Southern University, Statesboro, Georgia 30460, USAWe report the long-lasting bluish-green phosphorescence for X-ray or cathode ray tubes in the phosphors with compositions ofeither Ba2SiO4:0.01Eu2+–xSi3N4 x = 0–1 or 2BaCO3–ySi3N4:0.01Eu2+ y = 1/6–1 synthesized by a solid-state reaction. Bytuning the Si3N4 content, the phosphorescence may originate from Eu2+ in BaSi2O2N2 peaking at 490 nm, Ba2SiO4 505 nm,and Ba3SiO5 590 nm phases. The strong phosphorescence of the Ba2SiO4:Eu2+ phase in 2BaCO3–ySi3N4:0.01Eu2+ is attributedto N substitution for O to generate a shallow trap. In Ba2SiO4:0.01Eu2+–xSi3N4, however, N prefers reacting with Ba2SiO4 to formBaSi2O2N2, thereby exhibiting a strong phosphorescence of the BaSi2O2N2:Eu2+ phase but a weak phosphorescence of theBa2SiO4:Eu2+ phase.© 2009 The Electrochemical Society. DOI: 10.1149/1.3267513 All rights reserved.Manuscript received August 5, 2009. Published December 9, 2009.Long-lasting phosphorescence LLP is a phenomenon of ther-mally stimulated recombination of electrons and holes at traps,which leave holes or electrons in a long-lived excited state at roomtemperature, in which the luminescence of LLP materials persistsafter the removal of the excitation source.1 Since 1996, LLPSrAl2O4:Eu2+,Dy3+ with high brightness and long duration wasreported;2 more and more attention has been drawn to the exploita-tion of LLP materials for various displays, signing applications, lu-minous ceramics, safety indicators, optical data storage, etc.3-6Many LLP materials suitable for UV/visible light excitation havebeen reported,7-10 but those for X-ray and cathode ray tubes CRTsare seldom reported. Now, such LLP phosphors have been greatlyattractive due to their extensive applications.11,12 One of the appli-cations is for displaying radar echoes on the screen due to the longperiod of electron-beam rotation over the screen;13 the other appli-cation is for medical treatment equipments as an X-ray storage ma-terial under IR. Ba2SiO4:Eu2+ and BaSi2O2N2:Eu2+ are highly effi-cient bluish-green emitting phosphors for application in phosphor-converted white light-emitting diodes;14,15 however, their LLPproperties for X-ray or CRT excitation have not been demonstrated.In this paper, we report the LLP properties of BaSi2O2N2:Eu2+and Ba2SiO4:Eu2+ phases in the materials with the compositions ofBa2SiO4:0.01Eu2+–xSi3N4 x = 0–1 and 2BaCO3–ySi3N4:0.01Eu2+y = 1/6–1 for X-ray or CRT excitation. The role of N on the LLPis studied. The LLP phosphors are prepared by a solid-state reactionmethod under weak reductive atmosphere. The crystal structures,LLP, and thermoluminescence TL properties of phosphors are in-vestigated. Due to the similar properties of LLP for X-ray and CRTexcitation, X-ray is chosen to be an excitation source in this work.ExperimentalPowder samples can be synthesized by using a high temperaturesolid-state reaction method. One group of samples,Ba2SiO4:0.01Eu2+–xSi3N4 x = 0.03, 0.1, 0.2, 0.3, 0.5, 0.7, and 1.0,is prepared with Ba2SiO4:Eu2+ and Si3N4 as precursors, and thesynthesized process is described below. The starting materials usedwere BaCO3 analytical grade, SiO2 analytical grade, and Eu2O399.99%. These raw materials were taken in an agate mortar in astoichiometric molar ratio and were ground for 1 h, and then thepowder mixture was loaded into alumina crucibles and sintered at1100–1300°C for 4 h in a horizontal tube furnace under weak re-ductive atmosphere 5% H2 + 95% N2 mixed flowing gas. Afterslowly cooling to room temperature, in stoichiometric molar ratio,the fired product Ba2SiO4:Eu2+ was mixed with -Si3N4 and thenthe mixtures were ground in ethanol again for 1 h and sintered againat 1300–1500°C for 4 h in the same reducing gas flow as above. Theother group of samples, 2BaCO3–ySi3N4:0.01Eu2+ y = 1/6, 1/4,1/3, and 1.0 phosphors, was prepared. BaCO3 and -Si3N4 wereground in ethanol for 1 h in a stoichiometric molar ratio and weresintered at 1300–1500°C for 4 h in the same reducing gas flow asabove. The crystal structures of all synthesized samples were finallychecked using conventional X-ray diffraction XRD, Rigaku D/MAX-2500V with Cu target radiation at a 0.02° 2 scanning step.Photoluminescence, LLP spectra, and the decay curves of LLP weremeasured at room temperature using a fluorescent spectrophoto-meter F-4000, Hitachi Ltd., Japan equipped with X-ray as an ex-citation source. TL glow curves were measured using an OmegaCN76000 thermostat above room temperature. All measurementsexcept XRD and photoluminescence spectra were performed afterirradiated by X-ray excitation source for 5 min.Results and DiscussionThe crystal structures of Ba2SiO4:0.01Eu2+–xSi3N4, with x= 0.03, 0.1, 0.3, 0.5, 0.7, and 1.0, are characterized by XRD. TheXRD patterns of the samples are collected in the range of 20° 2  60°, as shown in Fig. 1. It exhibits that the XRD patterns ofthe samples are consistent with JCPDS no. 77-0150 for the Ba2SiO4orthorhombic phase when the Si3N4 content is equal to or less than0.1. However, with an increase in the content of Si3N4, theBaSi2O2N2 monoclinic phase is gradually formed and finally domi-nates the crystal phase as x = 1. The powder diffraction patterns ofBaSi2O2N2:Eu2+ are essentially the same as those reported by Li etal.16 and Bachmann et. al.17At room temperature, no LLP can be detected in Ba2SiO4:Eu2+after removing the X-ray or cathode ray excitation source. However,it is observed that Ba2SiO4:0.01Eu2+–xSi3N4 phosphors can gener-ate LLP originating from Eu2+ either in the Ba2SiO4 phase or theBaSi2O2N2 phase as x  0. Figure 2a shows the PL spectra ofBa2SiO4:Eu2+ and BaSi2O2N2:Eu2+ under excitation at 400 nm. Fig-ure 2b shows the LLP emission spectra ofBa2SiO4:0.01Eu2+–xSi3N4 x = 0.03, 0.1, 0.2, 0.3, 0.5, 0.7, and 1.0phosphors detected immediately after the removal of X-ray excita-tion source. When x = 0.03, weak LLP is detected, and phosphores-cence emission spectrum is in accordance with the PL spectrum ofBa2SiO4:Eu2+, peaking at about 505 nm. With increasing x from 0.1to 1, the LLP is enhanced continuously and the emission spectra ofLLP are no longer in accordance with the PL spectrum ofBa2SiO4:Eu2+ but in accordance with the PL spectrum ofBaSi2O2N2:Eu2+ only, peaking at 490 nm. In view of no LLP in purez E-mail: zhangjh@ciomp.ac.cnJournal of The Electrochemical Society, 157 2 H178-H181 20100013-4651/2009/1572/H178/4/$28.00 © The Electrochemical SocietyH178Ba2SiO4:Eu2+ at room temperature, it is speculated for the lowSi3N4 content x  0.1 in Ba2SiO4:0.01Eu2+–xSi3N4 that N3− ionsmay enter into the Ba2SiO4:Eu2+ lattices to replace O2− ions to formBa2SiO4:Eu2+,N3−, generating traps for room-temperature LLP. Forx  0.1, Si3N4 reacts with Ba2SiO4:Eu2+ to form BaSi2O2N2:Eu2+rather than to form Ba2SiO4:Eu2+,N3−. Although the XRD patternssee Fig. 1 indicate the Ba2SiO4 phase as a main crystal phase forx = 0.1, the LLP exhibits the behavior of BaSi2O2N2:Eu2+ as a sub-phase. This means that LLP prefers to appear in the BaSi2O2N2:Eu2+phase.The decay curves of LLP in Ba2SiO4:0.01Eu2+–xSi3N4 x = 0.1,0.2, 0.5, 0.7, and 1.0 are plotted in a double logarithmic coordinateafter the X-ray excitation source is switched off at room tempera-ture, as shown in Fig. 3. The decay curves approximatively fit thepower law of t−n, with n  0.75  1. Perhaps this results from theradiative recombination of electrons and holes through tunnelingand thermal hopping, as proposed by Yamaga et al.18 for understand-ing UV induced phosphorescence in Ba2SiO4:Eu2+ andBa3SiO5:Eu2+.Figure 4 shows the TL glow curves of Ba2SiO4:0.01Eu2+–xSi3N4x = 0, 0.03, 0.1, 0.2, 0.3, 0.7, and 1.0 measured above room tem-Figure 1. XRD patterns of Ba2SiO4:0.01Eu2+–xSi3N4 x = 0.03, 0.1, 0.3,0.5, 0.7, and 1.0.Figure 2. a PL spectra of Ba2SiO4:Eu2+ and BaSi2O2N2:Eu2+, b LLPspectra of Ba2SiO4:0.01Eu2+–xSi3N4 x = 0.03, 0.1, 0.2, 0.3, 0.5, 0.7, and1.0.Figure 3. Decay curves of Ba2SiO4:0.01Eu2+–xSi3N4 x = 0.1, 0.2, 0.5, 0.7,and 1.0.Figure 4. The TL glow curves of Ba2SiO4:0.01Eu2+–xSi3N4 x = 0, 0.03,0.1, 0.2, 0.3, 0.7, and 1.0.H179Journal of The Electrochemical Society, 157 2 H178-H181 2010perature. The samples are mounted in the thermostat and heated upat a heating rate of about 1.4 K/s in the temperature range of 300–500 K. The TL glow curve of Ba2SiO4:Eu2+ is composed of a domi-nant peak at 417 K and a shoulder at 374 K. Those peaks can beattributed to the intrinsic defects in the Ba2SiO4 host matrix. Due tohigh temperature locations, the two TL peaks therefore can hardlybe released at room temperature to generate LLP. When x = 0.03, aTL peak at about 355 K appears. Considering the observation of aroom-temperature LLP with an emission peak at 505 nm, the newTL peak at 355 K is attributed to the trap generated by N substitu-tion for O in the Ba2SiO4:Eu2+ host. With increasing x from 0.1 to 1,the 355 K peak disappears, but three other peaks located at about365, 320, and 335 K appear. When x is equal to 1, only the 335 Kpeak is observed in the TL spectrum of BaSi2O2N2:Eu2+, indicatingthat it could be the intrinsic TL peak of BaSi2O2N2:Eu2+. However,the appearance of 320 and 365 K peaks may be originated from thescarcity of N in the incomplete BaSi2O2N2:Eu2+ phase. The TL peaktemperature is generally proportional to the trap depth. The depth ofthe trapping centers can be estimated to beE = kTm2 /Twhere Tm is the temperature of the glow peaks, T is the high tem-perature half-width, and k is Boltzmann’s constant. The trap depthsof the intrinsic TL peaks of Ba2SiO4:Eu2+ and BaSi2O2N2:Eu2+phosphors are calculated by this formula, and the results are 0.493and 0.484 eV, respectively.Although the Eu2+ activated LLP of the Ba2SiO4 phase is ob-served in the Ba2SiO4:0.01Eu2+–xSi3N4 phosphors for a low x of0.03, the LLP is very weak. To obtain a strong LLP in the Ba2SiO4phase is our interest. Considering the generation of trap by N sub-stitution for O in the Ba2SiO4 phase, we synthesizedBa2SiO4:Eu2+,N3− with the starting materials of2BaCO3–ySi3N4–0.01 Eu2O3 by the solid-state reaction method ata reduction atmosphere. Figure 5 depicts the XRD patterns of2BaCO3–ySi3N4:0.01Eu2+ y = 1/6–1. When y is equal to 1/6, thecontent of Si3N4 may be too small to form a crystal phase but formsa eutectic mixture. The XRD patterns for x  1/6 are essentially inaccordance with JCPDS card no. 77-0150 for the Ba2SiO4 phase. Astrong LLP is observed in the 2BaCO3–ySi3N4:0.01Eu2+ phosphorsafter the removal of the X-ray excitation source at room tempera-ture. As shown in Fig. 6, when y = 1/6, the LLP spectrum shows asingle broad orange-red band with a maximum at 590 nm, whichshould belong to the Ba3SiO5:Eu2+ phase18 because the molar ratioof Ba/Si is 4:1 for y = 1/6, close to that of 3:1 in Ba3SiO5. Wheny  1/6, the LLP spectra show a typical emission band at 505 nm ofEu2+ in Ba2SiO4. The phosphorescence intensities increase with theincreasing Si3N4 content. Figure 7 shows the TL glow curve of the2BaCO3–Si3N4:0.01Eu2+ phosphor, which is composed of twopeaks located at 410 and 355 K, respectively. Thereinto, 410 K peakis the intrinsic TL peak of the Ba2SiO4:Eu2+ phase, as shown in Fig.4. As expected, a new strong TL peak is generated at 355 K. Thisnew TL peak is considered to be the N substitution for O inBa2SiO4:Eu2+ and plays an important role on room-temperatureLLP. Compared with the TL glow curve ofBa2SiO4:0.01Eu2+–xSi3N4 for x = 0.03, as shown in Fig. 4, the in-tensity of the 355 K TL peak of 2BaCO3–Si3N4:0.01Eu2+ is muchstronger, which results in an increase in LLP at room temperature.ConclusionsThe phosphors with compositions of eitherBa2SiO4:0.01Eu2+–xSi3N4 x = 0–1 or 2BaCO3–ySi3N4:0.01Eu2+Figure 5. XRD patterns of 2BaCO3–ySi3N4:0.01Eu2+ y = 1/6, 1/4, 1/3, and1.0.Figure 6. LLP spectra of 2BaCO3–ySi3N4:0.01Eu2+ y = 1/6, 1/4, 1/3, and1.0.Figure 7. The TL glow curve of 2BaCO3–Si3N4:0.01Eu2+.H180 Journal of The Electrochemical Society, 157 2 H178-H181 2010y = 1/6–1 are synthesized by a high temperature solid-state reac-tion method. Room-temperature LLP for X-ray or CRT excitation isobserved in the phosphors.1. The Ba2SiO4:0.01Eu2+–xSi3N4 phosphors show a weak LLPpeak at 505 nm of the Ba2SiO4:Eu2+ phase only for a small x 0.03. For 0.1  x  1, the LLP peak at 490 nm of theBaSi2O2N2:Eu2+ phase is dominant.2. 2BaCO3–ySi3N4:0.01Eu2+ phosphors show a weak LLP peakat 590 nm of the Ba3SiO5:Eu2+ phase only for small y  1/6. For1/4  y  1, a strong LLP of the Ba2SiO4:Eu2+ phase is detected tobe enhanced by a factor of 7 in comparison with that ofBa2SiO4:0.01Eu2+–xSi3N4 x  0.03.3. Pure BaSi2O2N2:Eu2+ exhibits a TL peak at 335 K, which isable to contribute to the room-temperature LLP. The TL peak ofpure Ba2SiO4:Eu2+ is located at a higher temperature of 417 K sothat no LLP can be detected at room temperature.4. The observed room-temperature LLP of the Ba2SiO4:Eu2+phase in either Ba2SiO4:0.01Eu2+–xSi3N4 x  0.03 or2BaCO3–ySi3N4:0.01Eu2+ 1/4  y  1 is attributed to N substi-tution for O to generate a new trap in the Ba2SiO4:Eu2+ phase. Theobserved TL peak at 355 K is considered to be the evidence of thenew trap.5. In Ba2SiO4:0.01Eu2+–xSi3N4, N prefers reacting withBa2SiO4 to form BaSi2O2N2 rather than replacing O in the Ba2SiO4phase, therefore exhibiting strong LLP of BaSi2O2N2:Eu2+ but veryweak LLP of Ba2SiO4:Eu2+.These results indicate that the blue-green emitting phosphors pre-sented in this paper could be promising LLP phosphors for X-ray orCRT. In view of a strong TL peak located at as high as 417 K,Ba2SiO4:Eu2+ could also be a material for X-ray storage used inmedical application.AcknowledgmentThis work was financially supported by the National Natural Sci-ence Foundation of China 10834006 and 10774141 and the MOSTof China 2006CB601104 and 2006AA03A138.Chinese Academy of Sciences assisted in meeting the publication costs ofthis article.References1. Y. L. Liu, B. F. Lei, and C. S. Shi, Chem. Mater., 17, 2108 2005.2. T. Matsuzawa, Y. Aoki, N. Takeuchi, and Y. Murayama, J. Electrochem. Soc., 143,2670 1996.3. J. Wang, S. B. Wang, and Q. Su, J. Mater. Chem., 14, 2569 2004.4. X. X. Wang, Z. T. Zhang, Z. L. Tang, and Y. H. Lin, Mater. Chem. Phys., 80, 12003.5. B. F. Lei, Y. L. Liu, J. Liu, Z. R. Ye, and C. S. Shi, J. Solid State Chem., 177, 13332004.6. S. Ye, J. H. Zhang, X. Zhang, S. Z. Lu, X. G. Ren, and X. J. Wang, J. Appl. Phys.,101, 063545 2007.7. F. Clabau, X. Rocquefelte, S. Jobic, P. Deniard, M. H. Whangbo, A. Garcia, and T.L. Mercier, Chem. Mater., 17, 3904 2005.8. Y. H. Lin, C.-W. Nan, X. S. Zhou, J. B. Wu, H. F. Wang, D. P. Chen, and S. M. Xu,Mater. Chem. Phys., 82, 860 2003.9. Q. Fei, C. K. Chuang, and D. L. Mao, J. Alloys Compd., 390, 133 2005.10. J. Y. Kuang and Y. L. Liu, Chin. Phys. Lett., 23, 204 2006.11. H. Yamamoto, Y. Morita, and H. Matsukiyo, J. Electrochem. Soc., 138, 27831991.12. S. Shionoya and W. M. Yen, Phosphor Handbook, CRC, New York 1998.13. Y. Nakanishi, H. Yamashita, and G. Shimaoka, Jpn. J. Appl. Phys., 20, 22611981.14. M. Zhang, J. Wang, Q. H. Zhang, W. J. Ding, and Q. Su, Mater. Res. Bull., 42, 332007.15. J. A. Kechele, O. Oeckler, F. Stadler, and W. Schnick, J. Solid State Chem., 11,537 2009.16. Y. Q. Li, A. C. A. Delsing, G. D. With, and H. T. Hintzen, Chem. Mater., 17, 32422005.17. V. Bachmann, C. Ronda, O. Oeckler, W. Schnick, and A. Meijerink, Chem. Mater.,21, 316 2009.18. M. Yamaga, Y. Masui, S. Sakuta, N. Kodama, and K. Kaminaga, Phys. Rev. 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Long-Lasting Phosphorescence in BaSi\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3eN\u3csub\u3e2\u3c/sub\u3e:Eu\u3csup\u3e2+\u3c/sup\u3e and Ba\u3csub\u3e2\u3c/sub\u3eSiO\u3csub\u3e4\u3c/sub\u3e:Eu\u3csup\u3e2+\u3c/sup\u3e Phases for X-Ray and Cathode Ray Tubes

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Long-Lasting Phosphorescence in BaSi\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3eN\u3csub\u3e2\u3c/sub\u3e:Eu\u3csup\u3e2+\u3c/sup\u3e and Ba\u3csub\u3e2\u3c/sub\u3eSiO\u3csub\u3e4\u3c/sub\u3e:Eu\u3csup\u3e2+\u3c/sup\u3e Phases for X-Ray and Cathode Ray Tubes

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