共沉淀流变相法制备LED荧光粉文献翻译.docx

Photoluminescence enhancement of YAG:Ce3+ phosphor prepared byco-precipitation-rheological phase method光致发光增强的YAG：Ce3 +的荧光粉制备共沉淀流变相法作者：YE Xinyu , LONG Zhen 2, YANG Youming, NIE Huaping, GUO Yanwei, CAI YufaAbstract: YAG:Ce3+ phosphor was prepared by a novel co-precipitation-rheological phase method. The resulting YAG:Ce3+ phosphor wascharacterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescent emission spectra. By using acetic acidas solvent, YAG:Ce3+ powder with small particle size （2 um） was obtained at a relatively lower sintering temperature of 1400 oC. With thecontent of acetic acid increasing, small particles dissolved and disappeared, but larger particles grew up and changed its shape from sphericalto partially rectangular. Meanwhile, the emission intensity of the sample prepared by co-precipitation-rheological phase method was about43% higher than that of the sample prepared by co-precipitation method. It was assumed that the significant improvement of luminescencewas mainly because the rheological phase presented a better diffusion environment, and therefore, a better homogeneity of activators of Ce3+.Keywords: phosphors; luminescence; YAG:Ce3+ co-precipitation-rheological phase method; rare earths摘要：YAG：Ce3 +荧光粉是用一种新型的共沉淀流变相法制备的。由此制备出的YAG：Ce3 +的荧光粉，通过X射线衍射（XRD），扫描电子显微镜（SEM）和光致发光光谱仪对合成的荧光粉进行了表征。通过使用醋酸作为溶剂，YAG:Ce3+粉末粒径小（2微米），可获得相对较低的烧结温度，约1400 OC。随着醋酸浓度的增加，小颗粒粉末溶解和消失，但较大的颗粒会变大并且它的形状会从球形变成的矩形。同时，通过共沉淀流变相法制备的样品的发光强度比共沉淀方法制备的样品发光强度高出约43。这里假设荧光粉发光显着改善，主要是因为流变阶段拥有一个更好的扩散环境，因此，更好地的使Ce3+激活为同质正离子。关键词：荧光粉发光; YAG：Ce3+共沉淀流变相法;稀土Compared with incandescent or fluorescent lamps, LEDbasedlight sources have many advantages such as superiorefficiency, long lifetime, high reliability and in particular,without mercury contamination. The combination of yellowphosphor YAG: Ce3+and blue LED is commonly used forwhite-light generation14. In this case, pure YAG phase isfavorable for luminescent properties of phosphors; however,the solid state reaction synthesis usually needs a high temperatureof 1600 oC to eliminate intermediate phases5,6. Additionally,so-produced powder is non-homogeneous andlarge in size, and irregular in shape, which greatly deterioratethe luminescent properties7. In general, phosphor with finesize (3 um) and spherical morphology is desirable for goodbrightness and high resolution8. Consequently, to obtainhigh-performance YAG:Ce3+phosphor, a variety of chemicalsynthesis techniques, such as co-precipitation process911,sol-gel process12,13, and combustion synthesis14,15 have beendeveloped in recent years. Co-precipitation method, due to itsfine homogeneity, high reactivity of starting materials andlower sintering temperature, is a preferred route to synthesizefine phosphor. However, it is still a challenge to obtain highlyluminescence phosphors with ideal morphology until now.与白炽灯或荧光灯相比，LED光源有许多优点，如出色的效率，寿命长，可靠性高，尤其是无汞污染。黄色荧光粉YAG：Ce3 +结合蓝色LED通常可产生白光1-4。在这种情况下，要获得好的发光性能纯净的荧光粉是非常有利的;然而，用固态反应物合成的方法通常需要1600 OC高温去消除中间阶段通5,6。而且，用这种方法制备的荧光粉不均匀，颗粒大，形状不规则，从而大大降低的发光性能7。在一般情况下，优良的尺寸，规则的球形是获得高亮度和高分辨率的理想荧光粉状态。因此，为了获得高性能的YAG：Ce3+荧光粉的化学合成技术，如水热合成法9-11，溶胶 - 凝胶法12,13，燃烧合成法14,15近年来被开发出来。共沉淀法，由于其优良的均匀性，高反应活性的起始原料和较低的烧结温度，综合而言是荧光粉合成的首选路线。然而，想要获得理想形态的高性能发光的荧光粉仍然是一个挑战。In the present study, we employed a novel co-precipitation -rheological phase method for the preparation ofYAG:Ce3+ phosphor. The rheological phase reaction is aprocess of preparing compounds or materials from asolid-liquid rheological mixture16. Due to a better homogeneity,the garnet phase was generated at a relatively low temperatureof 1400 C with fine size (2 um) and as a result,the phosphor had high photoluminescent intensity.在本研究中，我们采用了一种新方法：共沉淀流变相法去制备YAG:Ce3 +荧光粉。流变相反应是用固液状态的流变相混合物制备化合物或材料的过程。由于更好的同质化，石榴石固相体生成在相对低的温度为1400，并且颗粒尺寸小（2微米），因此荧光粉的发光强度高。1 Experimental1. 实验1.1 SynthesisThe YAG: Ce3+ samples were prepared by a co-precipitation- rheological phase method and the schematic diagram of the process is shown in Fig. 1. The starting materials Y(NO3)36H2O (A.R.), Ce(NO3)35H2O (A.R.) and Al(NO3)39H2O (A.R.) were dispersed in deionized water to form a homogeneous solution, in which total cation concentration was 0.2 mol/L and the atomic ratio of Y, Al and Ce was set to 2.94:5:0.06. Then, NH4HCO3 (1.2 mol/L) andsmall amount of (NH4)2SO4 were mixed as precipitant. The former solution was added dropwise into the precipitant at a flow rate of 5 ml/min with rapid stirring. After aging for 30 min, the as-prepared precipitation was filtered and further washed with deionized water and then ethanol. The purified precipitation was dried and then ground to get the precursor of YAG:Ce3+. When mixed with CH3COOH (A.R.), a uniform rheological phase system was obtained. The rheological phase system was heated at 80 C for 24 h in an airtight container. The powder thus prepared was put into a doublecrucible system and sintered at 600 C for 3 h in a reducing CO atmosphere. The obtained product was mixed with BaF2 (A.R.) and fired into YAG:Ce3+ phosphor at 1400 C for 3 h in a reducing COphosphor at 1400 C for 3 h in a reducing CO atmosphere.用共沉淀流变相方法制备YAG：Ce的样品。制备方法的过程示意图如图1所示。起始原料Y(NO3)36H2O (A.R.), Ce(NO3)35H2O (A.R.) 和Al(NO3)39H2O (A.R.)一起溶解在去离子水中形成均匀的溶液，其中总阳离子浓度为0.2 mol / L，Y：Al：Ce设置为2.94:5:0.06。然后，碳酸氢铵（1.2 mol / L）和少量的（NH4）2SO4混合沉淀。前面的方法是用5毫升/分钟的流量的速度将沉淀加入到溶液中快速搅拌。等待30分钟后，将所制备的沉淀，过滤，并进一步用去离子水和乙醇洗净（去除杂质）。将洗净的沉淀干燥，然后初步制成了YAG：Ce3 +的前驱体。再用它和乙酸（AR）的混合，获得一个统一的流变阶段系统。流变相系统在80C在密闭容器中加热24小时。并将制备的粉末放入一个双坩埚系统，并在600C高温，少量CO气体状态下预烧结3小时。获得的产物和BaF2 (A.R.)混合，再将混合物在少量CO气体环境下用1400 C高温烧结3小时，得到最终的YAG：Ce3+。Fig. 1 Schematic diagram of the co-precipitation-rheological phaseMethod图1.共沉淀流变相方法制备荧光粉的过程示意图1.2 Characterization1.2描述The crystal structure of phosphor was measured by X-ray diffraction (D8 ADVANCE, Bruker) with CuK (=0.15405 nm). The morphology was characterized by field emission scanning electron microscopy (S-4300, HITACHI). The emissionspectrum was detected by an F-4500 spectrophotometer (HITACHI).用X射线衍射仪（D8 ADVANCE, Bruker）测定铜的K辐射波长（=0.15405 nm）来确定荧光粉的晶体结构。用场发射扫描电子显微镜（S-4300, HITACHI）来观察表征荧光粉的形态。由F-4500型分光光度计（HITACHI）来检测荧光粉的发射光谱。2 Results and discussion2结果与讨论2.1 Phase analysis 2.1 物相分析The powder X-ray diffraction patterns of YAG:Ce3+ phosphors obtained by co-precipitation method and co-precipitation-rheological method are displayed in Fig. 2. All patterns agreed well with pure Y3Al5O12 phase (YAG, ICSD No. 20090). The YAG crystal belongs to the garnet-type structure in the cubic system with a=1.2009 nm and Ia-3d lattice symmetry. It is well known that pure YAG phase is favorable for luminescent properties of phosphors, but it normally needs a high temperature up to 1600 C to fabricate the pure YAG phase by solid-state reaction method using Al2O3 and Y2O3. Intermediate phases like YAlO3 (YAP, polymorphs structure) and Y4Al2O9 (YAM, monoclinic structure) frequently coexist with Y3Al5O12 (YAG,cubic structure) phase. But by using the co-precipitation-rheological phase method, it is indicated that pure YAG phase can be formed completely at a relatively low sintering temperature of 1400 C. This level of calcination temperature is significantly lower than that of heat treatment required in a conventional solid-state reaction. It fits well with the work of Zhang et al.17, who synthesized YAG:Ce3+ phosphor via a modified sol-gel method. Because of similar physical and chemical properties of Ce3+ and Y3+ especially in radius, electronegativity and reaction activity, cubic structure of YAG remains in YAG:Ce3+ 18. Compared with solid-phase synthesis, raw materials were mixed together at the molecular level in the liquid phase in co-precipitation method as well as in co-precipitation-rheological method, therefore, the precursors thus-prepared reduce the formation temperature of YAG phase, in this case, from 1600 to 1400 C due to small size, uniformity and high activity. 用共沉淀流变相法制备的YAG：Ce粉末的X-射线衍射图样如图2所示。所有的图案都是纯净的Y3Al5O12（YAG，ICSD的20090号）。 YAG晶体属于立方晶系a= 1.2009 nm，三维晶格对称系统中的石榴石型结构。大家都知道纯净的YAG相荧光粉对于提高发光性能是有利的，但它通常需要较高的温度，一般高达1600C，固态反应使用氧化铝和氧化钇的方法制备的纯净的YAG粉末。在中间阶段，YAlO3（YAP，晶型结构）和Y4Al2O9（YAM，单斜结构）经常与Y3Al5O12（YAG荧光粉，立方结构）相共存。但通过共沉淀流变相法，它表明纯YAG相完全可以在相对较低的烧结温度1400摄氏度下形成。这烧结温度的水平明显比传统的固态反应所需的热处理的温度低。通过溶胶 - 凝胶法来制备YAG荧光粉的张先生可以和我们合作来改进溶胶-凝胶法。由于Ce3+和Y3类似的物理和化学性能，尤其是在半径，电负性和反应活性方面相似，YAG：Ce3+的立方结构得以保持18。与固相合成法相比，原料在分子水平的液相共沉淀以及共沉淀流变方法混合在一起，因此，由于前期的沉淀准备降低了YAG相的形成温度。在这种情况下，反应温度从1600 C降至1400C，并且荧光粉的颗粒小，均匀性好和活性高。Fig. 2 XRD patterns of YAG:Ce3+ powders calcined at 1400 C (1) Prepared by co-precipitation method; (2) Prepared by co-precipitation-rheological method图2YAG:Ce3+荧光粉在1400C 的烧结温度下的X射线衍射图(1)共沉淀法制备的荧光粉；（2）共沉淀流变相法制备的荧光粉2.2 Morphology and particle size of YAG:Ce phosphor 2.2 荧光粉的形貌特征和颗粒大小The scanning electron microscopy images of final products using different amounts of acetic acid are shown in Fig. 3. YAG:Ce3+ powders in Figs. 3(a) and (b) consisted of nearly spherical particles with average particle sizes of 0.8 and 1.2 m, respectively. Further increasing the amount of acetic acid (Figs. 3(b)(d), the average particle sizes increased simultaneously from 1.2 m (200 wt.%) to 1.8 m (300 wt.%) and 2 m (400 wt.%), but the morphology changed from nearly spherical into partially rectangular shape. These results can be explained by the Ostwald Ripening Theory. 不同浓度的的醋酸所制备出的最终产品的扫描电子显微镜图像如图3所示。（a）和（b）由近球形颗粒组成，平均粒径0.8米，1.2米 ，随着醋酸量的进一步增加（b）-(d)段，平均粒径增加从1.2米（200 WT）至1.8米（300 WT）和2米（400 WT ）。但是形态却从近似球形变成矩形形状，这些结果可以用奥斯瓦尔德熟化理论来解释。Fig. 3 SEM images of YAG:Ce3+ using different amounts of acetic acid (a) 0 wt.%; (b) 200 wt.%; (c) 300 wt.%; (d) 400 wt.%图3.在不同醋酸浓度下制备的YAG：Ce3+样品的SEM图片In order to approach a stable state, the solid-liquid suspension system (rheological phase) tends to minimize its interface energy. Small particles in the system with high interface energy dissolve and eventually disappear, whereas big particles grow into partially rectangular shape. Additionally, it can be seen from the figure that the powder particles exhibited a good dispersion. This is probably because the steric effect of -OR groups of acetic acid medium (Fig. 4) hinders the agglomeration between the particles to great extent. 在固 - 液悬浮系统（流变阶段）往往尽量减少其界面能，去接近一个稳定的状态。在系统中的小颗粒具有高界面能，易溶解，并最终消失，而大颗粒部分则成长方形增长。此外，从图中还可以看出，粉末颗粒具有良好的分散性。这可能是因为空间位阻效应或醋酸介质组（图4）很大程度的阻碍了粒子之间的团聚。Fig. 4 Schematic diagram of precipitation particles in acetic acid图4.醋酸沉淀颗粒离子示意图2.3 Luminescence of YAG:Ce phosphor 2.3 YAG:Ce荧光粉的发光The phosphor of YAG:Ce3+ mainly belongs to the luminescent materials with individual luminescent center. Since the Ce3+ ion has only one electron in the 4f state, the impurity energy levels of Ce-doped crystals are particularly simple. The ground state is split into a 2F5/2 and a 2F7/2 level by the spin-orbit interaction. The first excited state originates from the 5d state, which interacts strongly with the host lattice because of the large spatial extent of the 5d wavefunction. Thus the crystal-field interaction dominates over the spin-orbit interaction and 4f5d transitions are parity and spin allowed. The images of YAG:Ce3+ precursor and YAG:Ce3+ phosphor are shown in Fig. 5, the YAG:Ce3+ phosphor instead of YAG:Ce3+ precursor exhibited an excellent yellow body-color, which is in good agreement with the product produced by conventional solid state reaction method. The emission spectra of YAG:Ce3+ phosphors under 460 nm excitation are demonstrated in Fig. 6. A broad band in the wavelength range of 490640 nm was observed in both of the spectra, which centered at 526 nm and originated from the 5d4f transition of Ce3+ ion. The emission intensity of the product produced by co-precipitation-rheological phase method was about 43% higher than that of the sample produced by co-precipitation method. It is well known that the increase of average particle sizes improves the luminescence to some extent. But in this case, it is assumed that the rheological phase played an important role in the significant enhancement of luminescence. The rheological phase formed by solid phases and acetic acid presented a better diffusion environment and then a better homogeneity of activators of Ce3+, which greatly enhanced the luminescence.YAG：CE3+荧光粉主要属于单个发光中心的发光材料。由于C Ce3+离子只有一个电子在4F状态，掺铈晶体的杂质能级，特别简单。基态分裂成由自旋轨道相互作用的2F5 / 2和2F7 / 2的准能级。第一激发态源于5D状态，主晶格因为5D波函数的空间范围大，有强烈的相互作用。因此在自旋轨道晶体场相互作用占主导地位，处于此能及的电子4f5d能够跃迁和自旋。前驱体YAG：Ce3 +的荧光粉的发光图像如图 5所示，在YAG：Ce3 +的荧光粉与YAG的前驱体相比展现了优异的黄光性能。与传统的固相反应法制备的荧光粉可以很好的比较。YAG：Ce3 +的荧光粉的发射光谱在460 nm激发下如图6所示。观察波长范围在490nm640nm之间的带宽的光谱分析图， Ce3+从5d跃迁到4f能级，发射出526nm的光波。共沉淀流变相法制备的产品的发光强度比共沉淀法制备的样品高出约43。这是众所周知的，因为平均粒径的增加在一定程度上提高了发光效率。在这种情况下，假定的发光效率的显著增强是因为流变阶段发挥了重要的作用。由固相和醋酸形成的流变阶段，提供了一个更好的扩散环境和更好的同质化的Ce3 +，从而大大提高了发光的流明效率。Fig. 5 Body-color of YAG:Ce3+ precursor (a) and YAG:Ce3+ phosphor(b)图5：荧光粉YAG:Ce3+前驱体（a）和荧光粉YAG:Ce3+ (b)的颜色相对发光强度 波长Fig. 6 Relative emission intensity of YAG:Ce3+ (ex=460 nm) (1) Prepared by co-precipitation method; (2) Prepared by co-precipitation-rheological phase method图6：YAG:Ce3+荧光粉的相对发光强度 (ex=460 nm)（1）共沉淀方法制备的样品（2）共沉淀流变相法制备的沉淀3 Conclusions3.总结YAG: Ce3+ phosphor was prepared by a novel co-precipitation -rheological phase method at a lower temperature of 1400 C. The X-ray diffraction patterns of the samples agreed well with pure Y3Al5O12 phase. With the amount of acetic acid increasing, average particle sizes increased but the morphology changed from nearly spherical into partially rectangular shape. The emission intensity of the sample prepared by co-precipitation-rheological phase method was about 43% higher than that of the sample prepared by precipitation method. The significant improvement of lumines cence was mainly because the rheological phase presented a better diffusion environment and therefore a better homogeneity of activators of Ce3+. 本实验用了一种新型方法共沉淀流变相法在相对较低的温度1400oC下来制备YAG: Ce3+荧光粉。样品的x射线衍射图与纯净的荧光粉相一致。随着醋酸浓度的增加，荧光粉颗粒平均粒径增加，但是颗粒形状却从近球形改变为长方形。共沉淀流变阶段方法制备的样品的发光强度比沉淀法制备的样品高出约43。荧光粉的发光效率显着改善，主要是因为流变阶段，提供了一个更好的扩散环境，因此更好的将Ce3 +离子的激活达到同质化。References: 参考文献1 Jacobs R R, Krupke W F, Weber M. Measurement of excited-state-absorption loss for Ce3+ in Y3Al5O12 and implications for tunable 5d4f rare-earth lasers. Appl. Phys. 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B, 2004, 107: 14. 8 Kang Y C, Lenggoro I W, Park S B, Okuyama K. YAG:Ce phosphor particles prepared by ultrasonic spray pyrolysis. Mater. Res. Bull., 2000, 35: 789. 9 Chiang C C, Tsai M S, Hsiao C S, Hon M H. Synthesis of YAG:Ce phosphor vi