CaSO_4:Eu荧光体的制备及其光致发光性质
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摘要
本论文主要研究了CaSO4:Eu荧光体的光致发光性质。主要内容有三部分构成：由CaSO4:Eu荧光体的合成条件探索了Eu在CaSO4中的存在价态、Eu2+的还原机理；在CaSO4:Eu中共掺其他金属离子研究了他们对Eu2+的发光性能的影响；利用柠檬酸自燃烧法及丙烯酰胺高分子网络凝胶法对CaSO4:Eu荧光体进行表面处理。结合FL、XRD、UV等测试手段得到如下结论：
（1） 以CaSO4为基质的发光材料的发光性能受合成工艺的影响比较大。起始原料、沉淀反应时溶液的pH值、烧结温度、时间及气氛都会对荧光体的发光性能产生明显的影响，其原因是上述工艺条件的变化影响荧光体的晶相纯度和激活剂离子所处的晶场环境。由于Eu3+与Ca2+半径相近，在晶化过程中可以以不等价方式取代基质CaSO4中的Ca2+，同时产生带负电荷的空位，这种空位将电子转移给Eu3+，导致Eu3+自身还原为Eu2+，即加入的Eu3+大部分被还原为Eu2+，还原后的Eu2+与附近的O2-离子形成了牢固的Eu-O共价键，生成了Eu2+（O2-）发光中心。荧光体主要表现为Eu2+的发光特性。
（2） 共掺离子浓度不是很大，基本上都不影响基质的晶型。稀土离子的共掺对Eu2+的发光强度的影响程度各有不同。La3+和Y3+是非荧光离子，在一定浓度下会对Eu2+的发光有增强作用。因为在SO42-的负电荷补偿下，Eu2+与La3+和Y3+离子可以进行不等价取代，Gd3+与Eu2+进行不等价取代的几率比La3+和Y3+小，但Gd3+与Eu2+之间可以发生微弱的Gd3+→Eu2+的能量传递。Ce3+→Eu2+的能量传递具有温度效应，是由于温度升高，CaSO4基质容易生成对称性更高的C2V结构，在此位置上，Ce3+容易还原为Ce2+，不发光的Ce4+和Ce2+增多，降低了Ce3+→Eu2+的能量传递。碱金属离子的掺入会降低CaSO4:Eu体系中Eu2+的发光，降低程度为Li>Na>K，源于半径越小的离子越容易进入晶格，而起到电荷补偿剂的作用，降低了Eu3+→Eu2+的转化效率。
（3） 用柠檬酸自燃烧法和聚丙烯酰胺高分子网络凝胶法均可以得到粒径为30-50 nm的CaSO4:Eu微粒，但在柠檬酸和聚丙烯酰胺的热分解过程中，增加了体系的温度，使CaSO4在低温下发生分解，生成CaO，并在646 nm左右出现明显的发射光谱。两种方法对微粒粒径、CaSO4的分解程度及光谱影响略有不同
The photoluminescent properties of CaSO4 doped with Eu2+ were inverstigated in this paper. This paper concluded three parts: the valence of Eu doped in CaSO4 and the conversion between Eu3+ and Eu2+ were discussed; the influence on the structure of CaSO4:Eu phosphors and the effects of other metal ions co-doped in CaSO4 on luminescence intensity were brought out; surface modification of CaSO4:Eu was made by using autocombustion of nitrate -citrate gel processing and the polyacrylamide gel processing. Some results were obtained by means of FL, XRD, UV and so on.
(1) Preparing conditions had great effects on the luminescent properties of Calcium sulfate phosphors. Raw material，pH valence, annealing temperature, annealing time and atmosphere had obvious effects on the crystal purity of Calcium sulfate host and environment of activators. Due to the radius of Eu3+ ion was close to that of Ca2+ ion, one negative vacancy could be created by the unequivalent substitution of Eu3+ for Ca2+. By thermal stimulation, electrons in these vacancies would be then transferred to Eu3+ ions. This results in the reduction of Eu3+ to Eu2+. Eu2+ created from reduction reaction would combine with a nearby O2-ion and form stable Eu-O covalent bond, in this way, Eu2+（O2-）luminescent centers were yielded. In the samples prepared by precipitation method, europium ions existed in CaSO4 host mainly in Eu2+ form.
(2) Crystal configuration of the host remained unchanged if concentration of doped metal ions was small. La3+ and Y3+ were non-luminescent ions. Addition of La3+ and Y3+ could enhance the luminescent intensity of Eu2+ doped in CaSO4 with definite concentration. It was found that the unequivalent substitution between Eu2+ and La3+ or Y3+ with the help of charge compensation role of SO42- ion. Probability of unequivalent substitution between Eu2+ and Gd3+ was smaller than La3+ or Y3+, but weak energy transfer of Gd3+→Eu2+ might be observed. Ce3+→Eu2+ energy transfer
process was obvious and under the influence of temperature, owing to the Ce3+ ion was reduced to Ce2+ ion more efficiently at sites of higher symmetry(i.e. C2v) which formed with the increasing of annealing temperature, resulted from both Ce2+ and Ce3+ did not give fluorescence, reduction as well as oxidation of Ce3+ would reduce the efficient of Ce3+→Eu2+ energy transfer. Addition of alkali metal ions would decrease the luminescent intensity of Eu2+ in CaSO4, the decrease degree was Li>Na>K. The less its radius, the easier the ion entered crystal lattice. As a charge compensation role, they decrease the efficiency of Eu3+→Eu2+ transfer.
(3) Nano-crystalline CaSO4:Eu might be prepared by autocombustion of nitrate -citrate gel method and the polyacrylamide gel method. The grain size of the powder was about 40 nm. Because the thermo-decomposition of citrate and polyacrylamide would improve the temperature of process, CaO would be yielded during decomposition of CaSO4, it resulted in that the emission located at 646 nm was obviously observed. We found that two processes had different effects on grain size, decomposition temperature and luminescent properties of samples
（1） 以CaSO4为基质的发光材料的发光性能受合成工艺的影响比较大。起始原料、沉淀反应时溶液的pH值、烧结温度、时间及气氛都会对荧光体的发光性能产生明显的影响，其原因是上述工艺条件的变化影响荧光体的晶相纯度和激活剂离子所处的晶场环境。由于Eu3+与Ca2+半径相近，在晶化过程中可以以不等价方式取代基质CaSO4中的Ca2+，同时产生带负电荷的空位，这种空位将电子转移给Eu3+，导致Eu3+自身还原为Eu2+，即加入的Eu3+大部分被还原为Eu2+，还原后的Eu2+与附近的O2-离子形成了牢固的Eu-O共价键，生成了Eu2+（O2-）发光中心。荧光体主要表现为Eu2+的发光特性。
（2） 共掺离子浓度不是很大，基本上都不影响基质的晶型。稀土离子的共掺对Eu2+的发光强度的影响程度各有不同。La3+和Y3+是非荧光离子，在一定浓度下会对Eu2+的发光有增强作用。因为在SO42-的负电荷补偿下，Eu2+与La3+和Y3+离子可以进行不等价取代，Gd3+与Eu2+进行不等价取代的几率比La3+和Y3+小，但Gd3+与Eu2+之间可以发生微弱的Gd3+→Eu2+的能量传递。Ce3+→Eu2+的能量传递具有温度效应，是由于温度升高，CaSO4基质容易生成对称性更高的C2V结构，在此位置上，Ce3+容易还原为Ce2+，不发光的Ce4+和Ce2+增多，降低了Ce3+→Eu2+的能量传递。碱金属离子的掺入会降低CaSO4:Eu体系中Eu2+的发光，降低程度为Li>Na>K，源于半径越小的离子越容易进入晶格，而起到电荷补偿剂的作用，降低了Eu3+→Eu2+的转化效率。
（3） 用柠檬酸自燃烧法和聚丙烯酰胺高分子网络凝胶法均可以得到粒径为30-50 nm的CaSO4:Eu微粒，但在柠檬酸和聚丙烯酰胺的热分解过程中，增加了体系的温度，使CaSO4在低温下发生分解，生成CaO，并在646 nm左右出现明显的发射光谱。两种方法对微粒粒径、CaSO4的分解程度及光谱影响略有不同
The photoluminescent properties of CaSO4 doped with Eu2+ were inverstigated in this paper. This paper concluded three parts: the valence of Eu doped in CaSO4 and the conversion between Eu3+ and Eu2+ were discussed; the influence on the structure of CaSO4:Eu phosphors and the effects of other metal ions co-doped in CaSO4 on luminescence intensity were brought out; surface modification of CaSO4:Eu was made by using autocombustion of nitrate -citrate gel processing and the polyacrylamide gel processing. Some results were obtained by means of FL, XRD, UV and so on.
(1) Preparing conditions had great effects on the luminescent properties of Calcium sulfate phosphors. Raw material，pH valence, annealing temperature, annealing time and atmosphere had obvious effects on the crystal purity of Calcium sulfate host and environment of activators. Due to the radius of Eu3+ ion was close to that of Ca2+ ion, one negative vacancy could be created by the unequivalent substitution of Eu3+ for Ca2+. By thermal stimulation, electrons in these vacancies would be then transferred to Eu3+ ions. This results in the reduction of Eu3+ to Eu2+. Eu2+ created from reduction reaction would combine with a nearby O2-ion and form stable Eu-O covalent bond, in this way, Eu2+（O2-）luminescent centers were yielded. In the samples prepared by precipitation method, europium ions existed in CaSO4 host mainly in Eu2+ form.
(2) Crystal configuration of the host remained unchanged if concentration of doped metal ions was small. La3+ and Y3+ were non-luminescent ions. Addition of La3+ and Y3+ could enhance the luminescent intensity of Eu2+ doped in CaSO4 with definite concentration. It was found that the unequivalent substitution between Eu2+ and La3+ or Y3+ with the help of charge compensation role of SO42- ion. Probability of unequivalent substitution between Eu2+ and Gd3+ was smaller than La3+ or Y3+, but weak energy transfer of Gd3+→Eu2+ might be observed. Ce3+→Eu2+ energy transfer
process was obvious and under the influence of temperature, owing to the Ce3+ ion was reduced to Ce2+ ion more efficiently at sites of higher symmetry(i.e. C2v) which formed with the increasing of annealing temperature, resulted from both Ce2+ and Ce3+ did not give fluorescence, reduction as well as oxidation of Ce3+ would reduce the efficient of Ce3+→Eu2+ energy transfer. Addition of alkali metal ions would decrease the luminescent intensity of Eu2+ in CaSO4, the decrease degree was Li>Na>K. The less its radius, the easier the ion entered crystal lattice. As a charge compensation role, they decrease the efficiency of Eu3+→Eu2+ transfer.
(3) Nano-crystalline CaSO4:Eu might be prepared by autocombustion of nitrate -citrate gel method and the polyacrylamide gel method. The grain size of the powder was about 40 nm. Because the thermo-decomposition of citrate and polyacrylamide would improve the temperature of process, CaO would be yielded during decomposition of CaSO4, it resulted in that the emission located at 646 nm was obviously observed. We found that two processes had different effects on grain size, decomposition temperature and luminescent properties of samples
引文
[1]张新夷，发光动力学。物理，1990，19（3）:179－184
[2]唐明道，稀土发光。物理，1990，19（6）:366－371
[3]S．T赫得逊，A．M马斯登 主编，灯与照明。1976，218
[4]J.M．P.J．Verstegen,A Survey of a Group of Phospors，Based on a Hexagonal Aluminate and Gallate Host Lattices，J．Electrochem，Soc．：Solid-State Science and Technology, 1974， 121（12）:1623－1627
[5]J.S. Choi, S.H. Baek, S.G. Kim, S.H. Lee, H.L. Park, S.I. Mho, T.W. Kim, Y.H. Hwang, Energy transfer between Ce3+ and Eu2+ in SrAl12O19:Cex3+,Eu0.012+ (x = 0.01-0.09), Materials Research Bulletin, 1999 34(4):551-556
[6] 满石清，石春山，晶场效应和化学键性质对Eu2+光谱结构的影响，化学学报，1991，48：648-652
[7]曹志成，石春山，倪嘉赞，关于低价稀土离子的发光，稀土，1992，13（5）：40-47
[8]石春山，叶泽人，复合氟化物中铕(Ⅱ)f-f跃迁发射的判据及其运用，化学学报，1989,47(11):1056-1060
[9] Blasse G., Structure and Bonding, 1976,26:43
[10] Sommerdijk J. L., Philips Technical Review, 1977, 37:221
[11] 石春山， 叶泽人，发光与显示，1982，4：1-10
[12]Pei Zhiwu, Su Qiang, J. Alloys and Compounds, 1993,198:51-53
[13] Thomas J . ustel, Helmut Bechtel, Walter Mayr, Detlef U. Wiechert
Blue emitting BaMgAl10O17:Eu with a blue body color， Journal of Luminescence， 2003 104：137–143
[14]Salis, M., On the photo-stimulated luminescence of BaFBr:Eu2+ phosphors， Journal of Luminescence, 2003,104(1-2):17-25
[15] Watanbe K.，Phjs．Rev.，195l，83:785
[16]T．Yamashita，N．Nada，Heath Phys.，197l，2l:295
[17]Morton J. R.，Ah1ers F. J.， Schneider C. C., Radiat. Prot. Dosim., 1993，47: 263
[18]罗达玲，徐则达等，硫酸镁的热释光和电子自旋共振特性研究，核技术，1996(2)：70
[19]Luo Daling，zhang Chunxiang，J．Phys．D: Appl. Phys.，1998, 31:902-912
[20]罗达玲，张纯祥等，核技术，一种高热稳定性的热释光材料MgSO4:Dy,Mn，1999，22（10）：604-608
[21]Luo daling，zhang Chunxiang，J．Phys．D：App1. Phys.，200l，34:
1533-1539
[22]zhang Chunxiang，Chen Lixin et al.，Radiahon Measurements，2000，32:123-128
[23]张纯祥，陈立新，唐强，罗达玲，丘志仁，掺入Dy和Mn的MgSO4磷光体的热释发光光谱，核技术，200l，24(1)：1-5
[24]U. Madhusoodanan, M.T. Jose, A.R. Lakshmanan， Development of BaSO4:Eu thermoluminescence phosphor，Radiation Measurements， 1999， 30：65-72
[25]Stephen W．S．McKeever，Report on Solid State Dosimetry Summer School:
A1hen，Greece，July，200l
[26] S.V. Godboleb, J.S. Nagpala, A.G. Pageb, UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors， Radiation Measurements，2000，32：343-348
[27] Xiong Gong, Pengfei Wu, Wai Kin Chan, Wenju Chen， Effect of γ-ray irradiation on structures and luminescent properties of nanocrystalline MSO4:xEu3+(M = Ca; Sr; Ba; x = 0:001-0:005)，Journal of Physics and Chemistry of Solids, 2000, 61:115-121
[28] A.P. Vink, E. van der Kolk, P. Dorenbos, C.W.E. van Eijk，Luminescent properties of Ce3+ in MSO4 (M: Ca, Sr and Ba) and the effect of Na+ co-doping, Optics Communications, 2002, 210:277–284
[29]A.P. Vink , E. van der Kolk, P. Dorenbos, C.W.E. van Eijk, Opposite parity 4fn-1 5d1 states of Ce3+ and Pr3+ in MSO4 (M=Ca, Sr, Ba), Journal of Alloys and Compounds，2002，341：338-341
[30] A.R. Lakshmanan， Photoluminescence and thermostimulated luminescence processes in Rare-earth-doped CaSO4 phosphors，Progress in Materials Science, 1999，44：1
[2]唐明道，稀土发光。物理，1990，19（6）:366－371
[3]S．T赫得逊，A．M马斯登 主编，灯与照明。1976，218
[4]J.M．P.J．Verstegen,A Survey of a Group of Phospors，Based on a Hexagonal Aluminate and Gallate Host Lattices，J．Electrochem，Soc．：Solid-State Science and Technology, 1974， 121（12）:1623－1627
[5]J.S. Choi, S.H. Baek, S.G. Kim, S.H. Lee, H.L. Park, S.I. Mho, T.W. Kim, Y.H. Hwang, Energy transfer between Ce3+ and Eu2+ in SrAl12O19:Cex3+,Eu0.012+ (x = 0.01-0.09), Materials Research Bulletin, 1999 34(4):551-556
[6] 满石清，石春山，晶场效应和化学键性质对Eu2+光谱结构的影响，化学学报，1991，48：648-652
[7]曹志成，石春山，倪嘉赞，关于低价稀土离子的发光，稀土，1992，13（5）：40-47
[8]石春山，叶泽人，复合氟化物中铕(Ⅱ)f-f跃迁发射的判据及其运用，化学学报，1989,47(11):1056-1060
[9] Blasse G., Structure and Bonding, 1976,26:43
[10] Sommerdijk J. L., Philips Technical Review, 1977, 37:221
[11] 石春山， 叶泽人，发光与显示，1982，4：1-10
[12]Pei Zhiwu, Su Qiang, J. Alloys and Compounds, 1993,198:51-53
[13] Thomas J . ustel, Helmut Bechtel, Walter Mayr, Detlef U. Wiechert
Blue emitting BaMgAl10O17:Eu with a blue body color， Journal of Luminescence， 2003 104：137–143
[14]Salis, M., On the photo-stimulated luminescence of BaFBr:Eu2+ phosphors， Journal of Luminescence, 2003,104(1-2):17-25
[15] Watanbe K.，Phjs．Rev.，195l，83:785
[16]T．Yamashita，N．Nada，Heath Phys.，197l，2l:295
[17]Morton J. R.，Ah1ers F. J.， Schneider C. C., Radiat. Prot. Dosim., 1993，47: 263
[18]罗达玲，徐则达等，硫酸镁的热释光和电子自旋共振特性研究，核技术，1996(2)：70
[19]Luo Daling，zhang Chunxiang，J．Phys．D: Appl. Phys.，1998, 31:902-912
[20]罗达玲，张纯祥等，核技术，一种高热稳定性的热释光材料MgSO4:Dy,Mn，1999，22（10）：604-608
[21]Luo daling，zhang Chunxiang，J．Phys．D：App1. Phys.，200l，34:
1533-1539
[22]zhang Chunxiang，Chen Lixin et al.，Radiahon Measurements，2000，32:123-128
[23]张纯祥，陈立新，唐强，罗达玲，丘志仁，掺入Dy和Mn的MgSO4磷光体的热释发光光谱，核技术，200l，24(1)：1-5
[24]U. Madhusoodanan, M.T. Jose, A.R. Lakshmanan， Development of BaSO4:Eu thermoluminescence phosphor，Radiation Measurements， 1999， 30：65-72
[25]Stephen W．S．McKeever，Report on Solid State Dosimetry Summer School:
A1hen，Greece，July，200l
[26] S.V. Godboleb, J.S. Nagpala, A.G. Pageb, UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors， Radiation Measurements，2000，32：343-348
[27] Xiong Gong, Pengfei Wu, Wai Kin Chan, Wenju Chen， Effect of γ-ray irradiation on structures and luminescent properties of nanocrystalline MSO4:xEu3+(M = Ca; Sr; Ba; x = 0:001-0:005)，Journal of Physics and Chemistry of Solids, 2000, 61:115-121
[28] A.P. Vink, E. van der Kolk, P. Dorenbos, C.W.E. van Eijk，Luminescent properties of Ce3+ in MSO4 (M: Ca, Sr and Ba) and the effect of Na+ co-doping, Optics Communications, 2002, 210:277–284
[29]A.P. Vink , E. van der Kolk, P. Dorenbos, C.W.E. van Eijk, Opposite parity 4fn-1 5d1 states of Ce3+ and Pr3+ in MSO4 (M=Ca, Sr, Ba), Journal of Alloys and Compounds，2002，341：338-341
[30] A.R. Lakshmanan， Photoluminescence and thermostimulated luminescence processes in Rare-earth-doped CaSO4 phosphors，Progress in Materials Science, 1999，44：1