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真空紫外用纳米蓝色发光材料的制备及发光性能研究
Preparation and Luminescence Properties of Nano Blue Phosphor under VUV Excitation
【作者】 王赵锋；
【导师】 王育华；
【作者基本信息】 兰州大学 ， 材料物理与化学， 2011， 博士
【摘要】 纳米发光材料由于其具有小尺寸效应、表面与界面效应、量子尺寸效应以及宏观量子隧道效应等,可以表现出块体材料所不具备的独特的发光性能而受到研究者们广泛的研究。此外,纳米发光材料还具有比块体发光材料更大的应用前景,如纳米发光材料可以用于制备微型显示设备,可以获得更高的显示分辨率,使画面更加生动清晰等,因此本论文主要考察了蓝色纳米发光材料的发光性能,并与传统块体材料进行比较。目前真空紫外商用蓝色荧光粉为BaMgAl10O17:Eu2+,它最主要的优点为具备较高的量子效率和好的色纯度。然而,在使用过程中尚存在两个主要问题：一是合成温度过高导致能耗大、生产成本高且产物易烧结；二是容易发生性能劣化。针对以上问题,我们采用sol-gel法成功地合成了纳米BaMgAl10O17:Eu2+,将其反应温度从传统固相法的1600℃降低至了1250℃。通过在sol-gel合成过程中添加一定量的表面活性剂十六烷基三甲基溴化铵,成功地获得了发光强度好、稳定性能优异的纳米BaMgAl10O17:Eu2+蓝色发光材料。为了进一步改善上述纳米样品的发光性能,使其能够达到应用的要求,我们在之前纳米样品的基础上进行了掺杂改性研究。通过在纳米BaMgAl10O17:Eu2+中共掺杂Ca2+和Mg2+,进一步提高了其发光性能与热稳定性,它的发光强度非常接近商用BaMgAl10O17:Eu2+蓝粉的发光强度,而热稳定性超过了商用粉。钨酸盐由于其在真空紫外具有广泛的吸收而有望成为一种非常好的真空紫外发光材料基质。本论文采用水热法合成了30nm、50nm和70nm的CaWO4蓝色发光材料,并研究了它们的发光性质。在不同纳米CaWO4材料中,发现其吸收峰发生了一定的蓝移,同时随着纳米CaWO4粒径的减小,其中的氧空位浓度逐渐增加。针对这一现象,我们尝试从CaWO4氧空位的形成能方面进行了解释。此外,我们在纳米CaWO4中还进行了Tb3+及Tb3++Yb3+的掺杂。在纳米CaWO4:Tb发光材料中,发现了其特有的高猝灭浓度现象,在保持Tb浓度一致的前提下,纳米CaWO4:Tb还表现出了比块体CaWO4:Tb更长的衰减时间。在CaWO4:Tb,Yb发光材料中,通过对其紫外-可见-近红外发光性质的研究,发现其中Tb与Yb之间存在能量传递。由于施主离子的特征发射和受主离子的特征激发不存在重叠,同时该两种离子存在能量传递且施主离子的发射能量是受主离子发射能量的两倍,证实了在CaWO4:Tb,Yb中发生了量子剪裁现象。通过对其量子效率的计算,得到掺杂0.01Tb与0.2Yb的CaWO4发光材料其量子效率可以达到140.4%,并且Yb3+的2F5/2-2F7/2发射与Si的带隙匹配较好,因此这种高量子效率的近红外量子剪裁发光材料在硅基太阳能电池方面具有潜在的应用。
【Abstract】 Recently, intense research activity has been focused on nano-sized luminescence materials regarding its unique optical characteristics comparing with the bulk phosphor. These natures are mainly caused by the small size effect, surface effect, quantum size effect and quantum tunnel effect. In addition, nanophosphor also exhibits some advantages on the aspect of the application that they are specially employed to acquire miniature luminescence device and high resolution display equipment. Therefore, this paper is mainly focus on the synthesis and investigation of photoluminescence of nanophosphors as well as comparing with the bulk phosphor.At present, the commercial blue phosphor for VUV application is BaMgAl10O17:Eu2+, which has the advantages of high quantum efficiency and good color purity. However, there are two serious problems of BaMgAl10O17:Eu2+ during the manufacture:one is the high reaction temperature leading to high energy consumption, high production cost and easily sintered; the other is the degradation of BaMgAl10O17:Eu2+ under the thermal and VUV irradiation treatment. Aiming at the above problems, we successfully synthesized BaMgAl10O17:Eu2+ nanophosphor by sol-gel method, which reduced the synthesis temperature about 350℃. Through the introduction of surfactant cetyl-tri-methyl-ammonium bromide (CTAB) in the sol-gel process,BaMgAl10O17: Eu2+ nanophosphor with good emission intensity and thermal stability was achieved. With the purpose of impelling BaMgAl10O17:Eu2+ nanophosphor for application, chemical doping was employed on the basis of the optimum condition. It was found that the codopant of Ca2+ and Mg2+ could further improve its photoluminescence, especially the thermal stability. The optimum nanophosphor presented a considerable emission intensity and higher thermal stability than the commercial one.Tungstates are expected to be the new hosts of VUV luminescence materials because of their broad absorption in VUV region. In this paper,30nm,50nm and 70nm of CaWO4 nanophosphors were synthesized by hydrothermal reaction. From the investigation of their luminescence properties, blue shift was observed in the absorption and excitation spectra. Besides, it was found in CaWO4 nanophosphors that the concentration of oxygen vacancy was increasing with the reduction of the particle size. A possible mechanism for the relationship was given based on the formation energy of oxygen vacancy in CaWO4 nanophosphor. In addition, we doped Tb3+ and Yb3+ in CaWO4 nanophosphor. The CaWO4:Tb nanophosphor presented the unique higher quenching concentration comparing with the bulk. By maintaining the concentration of Tb3+, the nano- CaWO4:Tb also exhibited longer life decay time than that of the bulk. For CaWO4:Tb, Yb luminescence material, the energy transfer from Tb to Yb was observed through the investigation of its UV-VIS-NIR luminescence properties. Due to the overlap between donor characteristic emission and acceptor characteristic absorption was absent and the sum of the absorption energy of the two acceptors equaled the emission energy of the one donor, NIR quantum cutting was proved in CaWO4:Tb, Yb. By calculating, the quantum efficiency of CaWO4:0.01Tb,0.2Yb reached 140.4%. According to the energy of Yb3+2F5/2-2F7/2 emission is just above the band gap of the crystalline Si, the material could be potentially applied in silicon-based solar cells.