氧化锌纳米晶体的发光原理

The luminescence of nanocrystalline ZnO particles:

the mechanism of the ultraviolet and visible emission

氧化锌纳米晶体粒子的发光：紫外发光与可见发光机理

Abstract (摘要)

Results of steady-state luminescence measurements performed on suspensions of nanocrystalline ZnO particles of different sizes are presented. (本文提供了对不同粒径大小的氧化锌纳米晶体粒子悬浮液的稳态发光测量结果。) In all cases two emission bands are observed.(在所有的例子中，观测到两个发光带。) One is an exciton emission band in the UV and the second an intense and broad emission band in the visible, shifted by approximately 1.5 eV with respect to the absorption onset. (第一个是存在于紫外区的激子发光带；第二个是存在于可见光区的强烈且宽的发光带，这个发光带的吸收起始点以约1.5eV进行变换。) As the size of the particles increases, the intensity of the visible emission decreases, while that of the exciton emission increases. (随着粒子大小的增加，可见区发光的强度减弱，而激子发光强度增加。)

In accordance with previous results, a model is presented in which the visible emission is assigned to the radiative recombination of an electron from a level close to the conduction band edge and a deeply trapped hole in the bulk (Vo**) of the ZnO particle. (根据之前的结果，提出了一个模型，可见发光是接近导带边缘水平的电子与氧化锌粒子本体（V o**）的深陷阱空穴的辐射再结合。) The size dependence of the intensity ratio of the visible to exciton luminescence and the kinetics are explained by a model in which the photogenerated hole is transferred from the valence band to a V o* level in

the bulk of the particle in a two-step process. (可见发光和激子发光之强度比的尺寸依赖性及动力学原理可由这样一个模型解释：在这个模型中，光致空穴通过一个两步的过程从低能满价带迁移到粒子本体的V o*水平。) The first step of this process is an efficient surface-trapping, probably at an O2- site.(这个过程的第一步，是极可能在O2-处的有效表面俘获。)

Keywords: Semiconductors; Nanoparticles; Quantum size effects; ZnO ( 关键词：半导体；纳米粒子；量子尺寸效应；氧化锌)

1.Introduction (引言)

ZnO has been known as a luminescent material for a century and nowadays it is used for various applications such as vacuum fluorescent displays (VFD's). (氧化锌作为一种发光材料，已经在一个世纪前为人们所知悉。如今，它有着广泛应用，如真空荧光显示器（VFD’s）。) However, despite numerous studies, the mechanism behind the visible luminescence has still not been established. (尽管有着大量的研究，但其在可见光区的发光机理仍未确立。) Much of the research on the luminescence of ZnO is performed on single crystalline powders or single crystals. (大量氧化锌发光的研究是基于单结晶粉末或者单晶体。) Two emission bands are usually found. (人们通常可以观测到两个发光带。) A relatively weak and narrow UV emission band is observed around 380 nm (3.25 eV), just below the onset of absorption. (一个是在波长为380nm（3.25eV）附近的较弱和较窄的紫外发光带，仅在吸收起始点之下。) This band is due to the radiative annihilation of excitons. (这个发光带是由激子的辐射湮灭所产生。) The lifetime of this exciton emission is very short, of the order of several tens to hundreds of picoseconds [1]. (激子发光的寿命是非常