【作者】 赵磊；

【导师】 王育华；

【作者基本信息】 兰州大学 ， 材料物理与化学， 2015， 博士

【摘要】 稀土离子掺杂的量子剪裁发光材料在等离子平板显示(PDPs)、无汞荧光灯以及硅基太阳能电池领域都有着非常重要的应用。目前,用于PDPs和无汞荧光灯领域的真空紫外发光材料都存在量子效率低的问题,而硅基太阳能电池也普遍存在光电转换效率非常低的问题,在这些领域中效率低的问题导致能量损失严重,造成了一定的资源浪费。针对这些问题,本论文选择几类典型的氧化物体系研究了在不同体系中稀土离子之间的能量传递和量子剪裁现象,主要得到如下三点结论：1.采用高温固相法成功的合成了GdBO3:Tb3+和KSr(Y,Gd)(PO4)2:Tb3+两种可见光量子剪裁发光材料。测试在样品在不同激发波长激发下的发射光谱,通过比较发射光谱中不同能级特征发射峰的相对强度,确认了在两类材料中均发生了由Tb3+-Tb3+之间通过交叉驰豫产生额外绿光发射的可见光量子剪裁现象。在高能真空紫外光子激发下,当Tb3+离子被激发到其4f75d高能级时,首先通过交叉弛豫作用将部分能量传递给一个与其相邻Tb3+,使其激发至其5D4能级,然后产生第一个可见光绿光光子的发射。而回到低激发态的Tb3+则非辐射跃迁至其5D3或5D4能级,产生第二个可见光光子5D3,4→7FJ的发射,从而在两种体系中实现了吸收一个高能真空紫外光子后通过能量传递发射出两个低能可见光光子的量子剪裁过程。在GdBO3:Tb3+和KSr(Y,Gd)(PO4)2:Tb3+两种材料中,最佳量子效率分别为174%和183%。2.一种近红外量子剪裁发光材料KCaGd(PO4)2:Ce3+,Yb3+通过硝酸盐热分解法成功合成。在紫外280nnm或者324nm激发下,样品的近红外发射光谱呈现出归属于Yb3+离子典型的2F5,2-2F5/2发射,发射范围位于900-1150nm,其峰值位于1021nm。由于Yb3+离子在紫外区并没有相应的能级存在,所以近红外区的发光只能由量子剪裁产生,这也就确认了量子剪裁的发生。其量子剪裁机理如下：在高能紫外光子激发下,体系中的Ce3+离子被激发其高能的5d能级,随后处于高能激发态的Ce3+离子弛豫到5d能级最低处,并且将能量通过合作能量传递的方式传递给相邻的两个Yb3+离子,使得Yb3+离子通过F5/2→2F7/2跃迁产生两个近红外光子的发射。体系中的量子效率随着Yb3+离子掺杂浓度的增大而增大,在324nm激发下体系的最佳的量子效率为158.2%。3.开发出两种Tm3+-Dy3+共激活的颜色可调发光材料Ba2Gd(BO3)2Cl和K3Gd(PO4)2。在近紫外激发下两种体系都可以通过Tm3+-Dy3+之间的共振能量传递实现颜色可调发射。系列样品在直接激发Tm3+至其1D2能级时,Tm3+ 1D2-3F4发射强度和Tm3+衰减时间的降低为体系中Tm3+→Dy3+;之间的能量传递现象提供了依据。随着Dy3+离子的掺杂浓度的增大,Tm3+→Dy3+能量传递效率也逐渐增大。根据Dexter’s多极相互作用共振能量传递理论,表明在Ba2Gd(BO3)2Cl:0.01Tm3+,xDy3+体系中Tm3+→Dy3+能量传递的机理为偶极-四极相互作用。在紫外激发下,两种体系可以通过稀土离子之间的下转换能量传递将一个高能的激发光子转换为低能的发射光子。Ba2Gd(BO3)2Cl: 0.01Tm3+,0.05Dy3+和K3Gd(PO4)2:0.01Tm3+, 0.08Dy3+的色坐标值分别为(0.352,0.328)为(0.338,0.347),与标准白光的(0.33,0.33)接近。更多还原

【Abstract】 Rare-earth-based quantum cutting phosphors have been extensively researched for their appliacation in PDPs, Mercury free lamps and Solar cells. In the present work, the phenomena of quantum cutting and energy transfer in oxysalts doped with different rare-earth ions have been investigated. The content of this paper includes three point:1. GdBO3:Tb3+ and KSr(Gd,Y)(PO4)2:Tb3+ phosphors were synthesize using the high temperature solid-state reaction method. The visible quantum cutting via cross relaxation between Tb3+ ions was observed via spectroscopic analysis. Upon excitation in the 4f75d1 states of Tb3+ in GdBO3:Tb3+and KSr(Gd,Y)(PO4)2:Tb3+, the quantum cutting occurred via a energy transfer process:the Tb3+ ion first relaxes from the 4f75d1state to an intermediate 5Dj state. During the relaxation, the released energy excites a neighboring Tb3+ to its 5D4 level by cross relaxation. Then, the original Tb+ and the neighboring Tb+ ions revert to their ground states by emitting two visible photons. The optimal quantum efficiency of GdBO3:Tb3+ and KSr(Y,Gd)(PO4)2:Tb3+ is 174% and 183%, respectively.2. A novel near-infrared (NIR) quantum cutting KCaGd(PO4)2:Ce3+,Yb3+ phosphor was successfully developed using the thermal decomposition of the corresponding nitrate. Due to the cooperative energy transfer from one Ce3+ to two Yb3+, an intense NIR emission around 1021 nm of Yb3+:2F5/2-2F7/2 transition was obtained under 324 and 280 nm excitation. Yb3+ concentration dependent quantum efficiency has been calculated and the theoretical maximum efficiency approaches up to 158.2%. Because the emission of Yb3+ around 1021 nm is matched with the band gap of crystalline Si, the phosphors could be a potential candidate for silicon-based solar cells.3. tm3+-Dy3+ co-activated Ba2Gd(BO3)2Cl and K3Gd(PO4)2 were synthesize using the high temperature solid-state reaction method. Upon direct excitation Tm3+ from its 6F6 level to 1D2 level, the decrease of emission intensity and lifetime of Tm3+1D2-3F4 emission with increasing concentration of Dy34 in Ba2Gd(BO3)2Cl: Dy3+, Tm3+ and K3Gd(PO4)2:Dy34, Tm3+ confirmed the occurrence of energy transfer from Tm34 to Dy34. Besides, Ba2Gd(BO3)2Cl:Dy3+, Tm3+ and K3Gd(PO4)2: Dy3+, Tm34 could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm34. For Ba2Gd(BO3)2Cl: 0.01Tm34, 0.05Dy34 and K3Gd(PO4)2:0.01Tm34,0.08Dy3+, intensive white emitting light with CIE of (0.352,0.328) and (0.338,0.347) was achieved upon 358 nm excitation.更多还原