【作者】 牟中飞；

【导师】 胡义华；

【作者基本信息】 广东工业大学 ， 应用化学， 2011， 博士

【摘要】 石榴石是一组在青铜时代已经广泛用作宝石的天然矿物。目前人工可以合成的用于发光材料的石榴石主要是钇铝石榴石及其一些变体。钇铝石榴石晶体是上个世纪六十年代首次合成的。七十年代,人们发现Ce3+掺杂的YAG可以发出强烈的黄光。进入九十年代以后,人们开始把YAG:Ce3+荧光粉与蓝光发光二极管(LED)搭配,利用二者混合而成的白光进行照明。虽然在之后的近二十年时间里,人们对稀土离子掺杂的YAG进行了大量的研究,取得了十分显著的成果,研究主要集中于制备工艺、掺杂改性、显色性、亮度、粒径控制等方面,以满足于实际生产的需要,但对于这种荧光粉的其它方面问题考虑较少,例如其它稀土或过渡金属离子在其中的光致发光以及热释发光性质,基质替代对于稀土或过渡金属离子在石榴石材料中的发光性质的影响,稀土或过渡金属离子在石榴石材料中的发光能量转移等问题。基于这些问题的存在,本论文采用高温固相法,制备了一系列稀土或过渡金属离子掺杂的钇铝石榴石材料,并研究了稀土或过渡金属离子的掺杂对于石榴石材料结构以及其中发光中心的发光性质的影响。主要获得了以下几个方面的成果：1、Ce3+在YAG中的余辉和热释光特性在1550℃灼烧4h可以制备纯相YAG, Ce3+的少量掺杂不改变基质YAG的结构。荧光光谱测试表明,还原气氛下制备的样品在峰值波长分别为341nm和455nm的宽带激发下,可以获得峰值波长531nm的宽带发射。在空气气氛下制备的样品中部分Ce4+可以自发的被还原成Ce3+,也可以形成531nm黄光发射。自还原样品中Ce4+的自还原并不彻底。紫外光激发以后,还原气氛下制备的样品在黑暗中可见黄色长余辉,余辉时间长达35min。而空气气氛下制备的Ce掺杂样品和无掺杂样品肉眼看不到长余辉现象。紫外激发后加热,Ce掺杂样品均存在较强的热释光。在弱还原气氛下制备的样品的热释光曲线上有112和256℃两个热释光峰；而在空气气氛下制备的样品的热释光曲线上只有128℃一个热释光峰。Ce3+掺杂样品的热释发光明显的强于无掺杂样品,证明Ce3+掺杂样品的热释发光主要来源于Ce3+。纯的YAG样品在受激后也有热释发光现象,其根源在于主要由反格位缺陷组成的本征缺陷以及样品合成过程中因杂质和空位所引起的非本征缺陷。Ce3+的掺入大大增加了样品中的陷阱浓度,降低了样品中的陷阱深度,导致样品在紫外激发下的长余辉发光。2、基质替代对于YAG的结构和发光性质的影响采用两种替代方式逐渐替代YAG基质中的阳离子,研究了基质替代对于YAG:Ce3+发光性质的影响。两种基质替代方式其一是用Dy3+替代Y3+,其二是用Ca2+和Si4+分别去替代Y3+和A13+。第一种替代方式：随着Dy3+含量的不断增加,Dy3+离子逐渐全部替代了Y2.95Al5O12: Ce3+0.05中Y3+的位置,表明YAG和DyAG二者之间可以形成完全互溶固溶体。在加入Dy3+时,样品的晶格逐渐发生膨胀,但保持原有的石榴石结构不变,其膨胀量与Dy3+含量成线性关系。样品的发射光谱均为宽带发射谱,随着Dy3+含量的不断增加,样品发射峰位发生红移,红移量也与Dy3+含量成线性关系。全部样品在紫外激发下都具有黄色长余辉现象,余辉时间最长达35min,样品的余辉时间随着Dy3+含量的增加而减小。经过热释光谱测量和计算,样品在紫外光照射下热释光谱上可见两个发射峰,低温峰位置随Dy3+含量的增加移向较低的温度,表明低温峰所代表的陷阱深度逐渐减小,有利于室温下陷俘电子的逃逸。样品在紫外激发下强的热释光效率,表明其在紫外辐射剂量测试方面有潜在的应用价值。第二种替代方式：随着Ca2+和Si4+的共替代量的不断增加,Ca2+和Si4+分别逐渐替代了Y2.95A15O12:Ce3+0.05中Y3+和A13+的位置,样品的晶格逐渐发生收缩,但保持原有的石榴石结构不变,其收缩量与共替代量成线性关系。样品的发射光谱均为宽带发射谱,随着共替代量的不断增加,样品发射峰位发生蓝移,蓝移量也与共替代量成线性关系。3、其它稀土和过渡金属离子在YAG中的发光性质Si4+被选作电荷和体积补偿剂与Mn2+共掺杂到YAG中,避免了电荷失衡问题,增大了Mn2+在YAG中的掺杂量,从而研究了Mn2+在YAG中的发光特性。根据引入的各离子半径,我们设计了两种替代方案,其一是Mn2+和Si4+分别替代Y3+和A13+；其二是Mn2+和Si4+共同替代A13+。样品的X射线衍射分析(XRD)表明,这样的两种替代方案均是可行的。两种替代方案中,Mn2+的掺杂量分别可以达到30和40mil%。在第一种替代中,由于掺入的两种离子均比替代的两种离子小,替代使基质YAG的晶格常数缩小,但在一定的限度(<30mil%)内并不改变原有的石榴石结构。样品的激发和发射光谱分析表明样品在紫外光和蓝紫光的激发下可以宽带发射峰值波长位于580-592nm的橙色荧光,其发光波长随着替代量的增加而红移。样品的发光强度在Mn2+掺杂量小于7.5mol%时随着掺杂量的增加而增加,大于7.5mol%时随着共掺杂量的增加而减小,即样品的发光强度在掺杂量为7.5mol%时取得最大值。样品在紫外光激发下可以长余辉发射橙色光,余辉时间最长达18min。通过对样品进行热释光测试发现共掺杂样品中存在两种不同深度的陷阱能级,而且它们的能级深度随着替代量的增加而减小,有利于室温下陷阱中被陷俘电子的释放。样品在紫外光激发下高的热释光强度表明其在紫外辐射剂量测试方面具有潜在的应用价值。在第二种替代中,掺入的两种离子一种比替代的离子大,另一种比替代的离子小其总的掺入效果是在一定限度内(<40mol%)使基质YAG的晶格常数缩小而不改变其石榴石结构。纯相样品的激发和发射光谱分析表明样品在紫外光和蓝紫光的激发下可以宽带发射峰值波长位于586-593nm的橙色荧光。样品的发光波长随着掺杂量的增加而红移。样品的发光强度在Mn2+掺杂量小于10mol%时随着掺杂量的增加而增加,大于10mol%时随着共掺杂量的增加而减小,即样品的发光强度在掺杂量为10mol%时取得最大值。4、稀土和过渡金属离子在YAG中发光能量转移通过采用Si4+作为电荷补偿剂,可以增大Mn2+在YAG中的掺杂量。在此基础上研究了Mn2+单掺杂磷光体Y3MnxAl5-2xSixO12的结构和发光性质。Mn2+在YAG中宽带发射峰值波长从586到593nm的橙色光,发光强度在Mn2+掺杂量为10mol%时达到最大,发光峰值波长随掺杂量的增加而红移。Tb3+单掺杂磷光体Y3-yTb3yAl5O12在275nm激发下,可见两组发射峰,分别对应于激发态5D3和5D4到基态7FJ(J=6、5、4、3)的跃迁。将Tb3+、Mn2+共掺于YAG中,Tb3+的发光对于Mn2+的发光具有明显的敏化作用,发生了从Tb3+到Mn2+的能量转移。经分析,发生能量转移的原因在于Tb3+的发射光谱与Mn2+的激发光谱有较好的重叠。本文的实验和分析证明,电荷补偿和其它发光中心离子的敏化是提高Mn2+在YAG中发光强度的两个有效途径。合成了一系列Bi3+和Dy3+共掺杂的YAG,并研究了两种离子在YAG中的发光和从Bi3+到Dy3+的能量转移。Bi3+在276nm紫外光的激发下可以发射峰值波长位于304nm的宽带,起源于Bi3+从激发态3P0,1到基态1So的跃迁。Dy3+在YAG中可以发射两组发射峰,分别位于484和583nm附近,可分别归属为从激发态4F9/2到基态6H15/2和6H 13/2的跃迁。把Bi3+共掺入Dy3+单掺杂系统,Dy3+的发射显著增强。Dy3+的发射强度显著增强,证明发生了从Bi3+到Dy3+的共振能量转移,原因在于Bi3+的发射光谱和Dy3+的激发光谱之间有明显的重叠。经分析,二者之间的共振能量转移是通过“电偶极—电四极”相互作用引起的。5、Eu3+在Sr2CeO4及ZnB2O4中发光的电荷补偿在Sr2Ce04体系中,荧光粉可以强烈的宽带吸收紫外线,其峰值波长为276nm,覆盖低压汞灯的主要发射波长(254nm)。实验确定Eu3+在Sr2Ce04中的最优掺杂浓度是x=0.13。所用到的四种电荷补偿方法都能够增强Eu3+的红光发射强度而不改变其激发和发射光谱的形状和位置。Li+,Na+或K+取代Sr2+, Al3+取代Ce4+可以分别把Eu3+的红光发射增大到1.3,1.6,2.1和1.4倍。研究表明Eu3+重掺杂的电荷补偿的Sr2Ce04是一种可以用于低压汞灯及方兴未艾的AlxGa1-xN基紫外LED的优秀红色荧光粉。在ZnB2O4体系中,XRD结果显示所制备的样品几乎是纯相。Eu3+在ZB中可以强烈吸收393nm紫外光发出色纯度较好的红光。电荷补偿可以提高样品的结晶度,增加其红光发射强度,还可以改善红光发射的色纯度。但不同的电荷补偿方法均不影响激发和发射光谱的位置和形状。Li+的补偿效果最好,其次是Na+,K+和自补偿。这几种方法分别可以将红光发射增大到4.4,3.7,3.4和2.2倍。样品的形貌分析表明制备的样品是不均一的,电荷补偿剂的引入改善了样品的结晶度,因而增加了样品的平均晶粒度。当发光中心在基质中取代的是一种与之不等价的离子(如Eu3+取代Sr2+, Ca2+, Ba2+或Zn2+)时,发光中心的掺杂量将受到限制。在这种情形下,电荷补偿是一种增强发光中心发光强度的有效手段。单从电荷平衡的角度考虑,当发光中心离子所带正电荷比所替代离子多时,所选择的补偿离子所带正电荷应该比它所替代的离子少,反之亦然。发光中心离子和补偿离子可以同时取代基质中的同一种阳离子,也可以分别取代两种阳离子。然而,单从电荷平衡的角度考虑还是不够的,在满足电荷平衡的同时还要考虑其它两个方面：一是离子数的平衡,即1个离子只能取代1个离子；二是体积平衡,即如果发光中心离子比它所替代的离子大,那么补偿离子就应该比它所替代的离子小,反之亦然。更多还原

【Abstract】 Garnets are a group of minerals which have been widely used as gems as early as Bronze Age. Garnets which can be synthesized artificially to be used as luminescent materials include yttrium aluminium garnet (Y3Al5O12, YAG) and some modifications of its. In 1960s, the single crystal of yttrium aluminium garnet was synthesized for the first time. In 1970s, people found that Ce3+ doped YAG can emit intense yellow light. When it comes to 1990s, phosphor YAG:Ce3+ began to be combined with blue light-emitting diodes (LEDs). Obtained white light can be used as a light source for interior illumination. In the subsequent nearly twenty years, people spent plenty of time and efforts in the investigation of this phosphor and obtained remarkable achievements. These investigations mainly focus on the preparation techniques, the improvement or modification of luminescence properties by doping, chromaticity, the enhancement of brightness, the controlment of particle size, and so on, to fulfill the requirements in practical production. However, the other problems were ignored such as the photoluminescence and thermoluminescence (TL) properties of the other rare earth (RE) ions and transition metal (TM) ions in garnets, the effect of host substitution on the luminescence properties of RE or TM ions in garnets, luminescence energy transfer of these ions in garnets, and so on. Thus, a series of RE or TM ions doped YAG or its modifications were synthesized with solid state reactions. The effect of the doping of RE or TM ions on the structure and luminescence properties were investigated. The main conclusions obtained in this dissertation were as follows.1. Afterglow and TL properties of Ce3+ in YAGPure YAG can be obtained by sintering the raw material for 4h at 1550℃. The doping of Ce3+ with a small amount does not change the structure of host YAG.The measurement of fluorescence spectra show that the sample prepared in reducing atmosphere can emit a broad band peaking at 531nm under the excitation of 341 and 455nm. Ce4+in the sample prepared in air can be partly reduced to Ce3+ spontaneously. Thus it can also emit yellow light peaking at 531nm. The luminescent intensity of the sample prepared in air is about one third of the intensity of the sample prepared in a reducing atmosphere. This indicates that the spontaneous reducing in air is incomplete. Under the ultraviolet excitation, yellow long afterglow can be found in the sample prepared in reducing atmosphere. The afterglow time is as long as 35 minutes. While there is no long afterglow is observed in Ce3+ doped YAG prepared in air and undoped YAG:Ce3+ doped samples show obvious thermoluminescence after they are excited by ultraviolet (UV) light.There are two TL peaks at 112 and 256℃respectively in the TL spectrum of reduced sample. However there is only one at 128℃in the sample prepared in air. The TL of Ce3+ doped samples is obviously stronger than the undoped one. This indicates that TL is originated from doped Ce3+. There is also TL in pure YAG after UV excitation which is originated from the extrinsic defects introduced by the impurity formed in the synthesis process and intrinsic defects mainly composed or anti-site defects. The doping of Ce3+ increases the concentration of defects remarkably and decreases the depth of defect energy level. This results in the long afterglow of samples under UV excitation.2. Effect of host substitution on the structure and luminescence properties of Ce3+ in YAGThe cations in YAG were gradually substituted with two methods. Then the effect of host substitution on the structure and luminescence properties was investigated in detail. One method is to substitute Y3+ with Dy3+. The other one is to substitute Y3+ and Al3+ with Ca2+ and Si4+ respectively.For the first substitution method Dy3+ gradually replaces Y3+ in Y2.95Al5O12:Ce3+ 0.05 with the increment of Dy3+ content. This indicates that YAG and DyAG can form complete solid solution. The crystal lattice expand with the increment of Dy3+ content but keep original garnet structure unchanged. The expansion extent of crystal lattice is proportional with Dy3+ content. The emission of all the samples is in a broad band. However, with the increment of Dy3+ content, a red-shift of emission peak is observed. The red-shift extent is also proportional with Dy3+ content. Long afterglow can be observed for all the samples. Afterglow time decreases with the increment of Dy3+ content with the longest afterglow time of 35 minutes. Via the measurements and calculation on TL spectra, two TL peaks can be found in the TL spectra. Position of the peak with lower temperature moves to lower temperature with the increasing Dy3+ content. This indicates that the depth corresponding to the peak with lower temperature decreases with the increasing Dy3+ content which is advantageous to the release of trapped electrons. The satisfying TL efficiency indicates our phosphor have potential applications in UV radiation dosemeters.For the second method, with the increment of co-substitution content, Ca2+ and Si4+ replaced Y3+ and Al3+ respectively, which results in the shrink of crystal lattice of samples whereas it presents single garnet structure all along. The decrement of cell parameter is in linear with the increment of co-substitution content. The emission spectra of all samples are in a broad band. The peak wavelength of the emitted broad band shows a blue-shift and the amount of the blue-shift is also in linear with the co-substitution content.3. Luminescence properties of the other RE and TM ions in YAGSi4+is co-doped into YAG with Mn2+ as a charge and volume compensator. This avoids charge unbalance and increases the doping content of Mn2+ in YAG. On the basis of this, the luminescence properties of Mn2+ in YAG are investigated. According to the radii of introduced ions, we design two methods for the substitution of Mn2+ and Si4+. One is to replace Y3+ and Al3+ with Mn2+ and Si4+ respectively. The other is to replace Al3+ with both Mn2+ and Si4+. The results of X-ray diffraction (XRD) analysis indicate that both methods are practical. The maximal doping concentration of Mn2+ in two methods can be enhanced to 30 and 40mol% respectively.For the first method, the substitution of Mn2+ and Si4+ to Y3+ and Al3+ make the interplanar distance decrease but does not change the single garnet crystal phase of the samples because the radii of both doped ions are smaller than replace ones.The emission spectra show that samples can emit yellow-orange light in a broad band peaking from 579 to 592 nm with long afterglow under the excitation of UV and blue-violet light. With the increment of substitution content, the emission intensity of samples increases firstly, decreases subsequently. The highest emission intensity occurs when x=0.075. The emission peaks move to longer wavelength. Afterglow spectra and decay curves show that all the Mn2+ and Si4+ co-doped samples emit yellow-orange light with long afterglow after the irradiation of UV light. The longest afterglow time is 18 minutes for Sam3.Two kinds of traps with different energy level depth in co-doped samples were observed by means of TL detection, and their depth decreases with the increment of substitution content. Higher TL efficiency shows that the phosphors present a good potential for UV irradiation dosimeter applications.For the second method, the co-doping of Mn2+ and Si4+ makes the interplanar distance decrease but does not change the single garnet crystal phase of the samples in a certain extent. The excitation and emission spectra of samples with pure crystal phase show that samples can broadband emit orange light peaking at 586nm to 593nm under the excitation of UV light and blue-violet light. With the increment of co-doping content, the emission intensity of the phosphors increases when Mn2+ content is lower than 10mol% while decreases when it is higher than 10mol%. That is to say, the emission intensity is biggest when Mn2+ content is 10mol%. The emission peak moves to longer wavelength with the increment of co-doping content.4. Luminescence energy transfer of RE and TM ions in YAGBy employing Si4+ as a charge compensator, the doping content of Mn2+ in YAG was increased to a certain extent. On this basis, the structure and luminescence properties of Mn2+ singly doped phosphor were investigated. Mn2+ in YAG emits orange light in a broad band. With the increment of the doping content, the emission peak shifts to longer wavelength and the emission intensity of phosphors increases firstly, decreases subsequently. The emission intensity reaches its maximum when Mn2+ content is 10mol%. Two groups of emission peaks, corresponding to the optical transitions from excited states 5D3 and 5D4, to ground state 7F1(J=6,5,4,3), respectively, were observed in the emission spectra of Tb3+ singly doped phosphors. When Tb3+ and Mn2+ were co-doped into YAG, the obvious sensitization effect of Tb+ on Mn+ was observed which indicates that the energy transfer from Tb3+ to Mn2+ occurs. The reason for energy transfer from Tb3+ to Mn2+ is verified that there is a perfect overlapping between the emission spectrum of Tb3+ and excitation spectrum of Mn2+. The experiments and analysis confirm that charge compensation and the sensitization of the other luminescent ions are two effective methods which can be utilized to enhance the luminescence of Mn2+ in YAG.A series of Bi3+ and Dy3+ doped YAG were synthesized with solid state reactions. The luminescence properties of Bi3+ and Dy3+, and the energy transfer from Bi3+ to Dy3+ were investigated. Bi3+ in YAG emits one broad band peaking at 304nm under the excitation of UV light (276nm) which is attributed to the transition from excited states 3P0.1 to ground state1So.Dy3+ in YAG emits two groups of emission lines near 484 and 583nm respectively which are attributed to the transitions from excited state 4F9/2 to ground states 6H15/2 and 6H13/2. The co-doping of Bi3+ into Dy3+ doped YAG enhances the luminescent intensity of Dy3+ by-7 times. The remarkable enhancement of Dy3+ emission obtained by Bi3+ co-doping makes it possible that Dy3+ doped phosphors are used in w-LEDs. The enhancement also proves the occurrence of resonance energy transfer from Bi3+ to Dy3+ which results from the overlapping between the emission spectrum of Bi3+ and the excitation spectrum of Dy3+. The resonance energy transfer from Bi3+ to Dy3+ is performed through dipole-quadrupole interactions.5. Charge compensation for the luminescence of Eu3+ in Sr2 CeO4 and ZnB2O4For the first system (Eu3+ doped Sr2CeO4), the phosphors can strongly absorb UV (broad band peaking at 276nm and overlapping 254nm) which is coupled well with the emission of low pressure mercury vapor (LPMV) lamps. In our experiments, the optimal doping concentration of Eu3+ in Sr2CeO4 is ascertained(x=0.13). All four charge compensators can enhance the red emission of Eu3+, but they do not significantly change the shape and positions of excitation and emission spectra in the same host lattices. The introduction of Li+, Na+ and K+ at Sr2+ site, Al3+ at Ce4+ site can enhance the luminescent of red emission by 1.3,1.6,2.1 and 1.4 times respectively. The investigation in this paper indicates that Eu3+ heavy doped Sr2CeO4 phosphors with charge compensation are potential candidates of red emitting phosphors for LPMV lamps or ascending AlxGa1-xN-based UV LEDs.For the second system (Eu3+ doped ZnB2O4) the results of XRD analysis show that all the prepared samples can be indexed to pure phase ZnB2O4. The excitation and emission spectra of samples show that Eu3+ doped ZnB2O4 can strongly absorb 393nm UV light which is coupled well with the emission of currently used InGaN-based near UV LEDs and emit red light with good color purity. Employed four charge compensation approaches can not only improve the crystallinity but also enhance the red emission of phosphors. Different charge compensation approaches do not affect the shape and position of excitation and emission spectra. The compensation effect of Li+ is the optimal followed by Na+, K+ and self-compensation. They can enhance the red emission intensity of Eu3+ by 4.4,3.7,3.4 and 2.2 times, respectively. Morphology analysis of samples with a scanning electronic microscope indicates that prepared samples are inhomogeneous and the introduction of charge compensators improves the crystallinity and increases the mean particle size of phosphors.When an ion as a luminescent center replaces another one which has the different valency(such as the substitution of Eu3+ for Sr2+, Ca2+, Ba2+ or Zn2+), the substitution content will be restricted. On this condition, charge compensation is an effective method for the enhancement of luminescence intensity. If just charge balance is taken into consideration, selected compensating ion should own less positive charges than replace ion when luminescent center ion has more positive charges than replaced ion, vice versa. Luminescent center ion and compensating ion may replace the same ion in the host. They can also replace the different ions. However, it is deficient to take just charge balance into consideration. When a charge compensator is selected, two other aspects should also be thought. One is the equilibrium of mole number which requires that one ion can only replace one. The other is volume balance. If luminescent center ion is bigger than replaced ion, the compensating ion should own a smaller radius than replaced ion by it, vice versa.更多还原