Luminescent Properties in Relation to Controllable Phase and Morphology of LuBO3:Eu3+ Nano/Microcrystals Synthesized by Hydrothermal Approach

The calcite and vaterite type LuBO3:Eu3+ nano/microcrystals with various morphologies were synthesized by the hydrothermal (HT) approach through controlling the pH values of the precursor solutions. The calcite type LuBO3:Eu3+ shows the dominant magnetic dipole D-5(0)-F-7(1) emission due to S-6 inversion symmetry of Lu. It also shows a symmetrical O-Eu charge transfer (CT) excitation band, which, however, is asymmetrical and broad in the material prepared by the solid-state (SS) reaction method. The effect of the residual OH- groups introduced in HT synthesis is discussed on O-Lu exciton annihilation and local environment distortion. Two different Eu3+ centers, one of which is with inversion symmetry, are observed in vaterite type LuBO3:Eu3+ The HT sample with nanostructures, such as vaterite type flowerlike LuBO3:Eu3+, demonstrates a red shift of the CT band and appearance of a long excitation tail at the long wavelength side of the CT band. XRD, selective excitation and fluorescence decay measurements indicate that the red shift is induced by an increase of crystal lattice parameters, and the excitation tail is responsible to the Eu3+ ions located at lower symmetric sites. These sites are attributed to the positions at or close to the surface of the nanostructures in the sample. As the lower symmetric sites are selectively excited, the red emission of D-5(0)-F-7(2) of Eu3+ enhanced twice relatively to the orange emission of D-5(0)-F-7(1), exhibiting superior color chromaticity in red for display application. The luminescence properties of interior Eu3+ and outside Eu3+ are studied and discussed in detail.

通过控制前驱体溶液的pH值，采用水热（HT）方法合成了具有不同形貌的方解石型和球霰石型LuBO₃:Eu³⁺纳米/微晶。方解石型LuBO₃:Eu³⁺由于Lu的S₆反演对称性，呈现出占主导的磁偶极D₅⁽⁰⁾ - F₇⁽¹⁾发射。它还显示出一个对称的O - Eu电荷转移（CT）激发带，然而，在固态（SS）反应法制备的材料中，该激发带是不对称且宽的。讨论了水热合成中引入的残余OH⁻基团对O - Lu激子湮灭和局部环境畸变的影响。在球霰石型LuBO₃:Eu³⁺中观察到两种不同的Eu³⁺中心，其中一种具有反演对称性。具有纳米结构的水热样品，如球霰石型花状LuBO₃:Eu³⁺，表现出CT带的红移以及在CT带长波长侧出现长激发尾。X射线衍射（XRD）、选择性激发和荧光衰减测量表明，红移是由晶格参数增加引起的，激发尾是由位于低对称位点的Eu³⁺离子导致的。这些位点归因于样品中纳米结构表面或接近表面的位置。当低对称位点被选择性激发时，Eu³⁺的D₅⁽⁰⁾ - F₇⁽²⁾红色发射相对于D₅⁽⁰⁾ - F₇⁽¹⁾橙色发射增强了两倍，在用于显示应用的红色方面表现出优异的色度。对内部Eu³⁺和外部Eu³⁺的发光特性进行了详细研究和讨论。