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 inthe 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短的，量级在几十到几百皮秒。
) A much stronger and broader emission band is situated in the green part of the visible spectrum, with a maximum between 500 and 530 nm (2.35～2.50 eV). (另一个强得多和宽得多的发光带，位于可见光谱的绿光区处，最大波长在500～530nm(2.35-2.50eV)之间。
) In contrast to the exciton emission, the lifetime of the visible emission is much longer, viz. in the us range [2]. (相对于激子发光，可见发光的寿命要长得多，以微秒计。
) For this report, quantum-sized ZnO particles are used. (在这份报告中，使用的是量子尺寸的氧化锌粒子。
) The mean particle size can be varied and its influence on the emission properties can be used to obtain information on the nature of the visible emission. (平均粒子尺寸有所变化，粒子尺寸变化对发光性能的影响可用来获取关于可见发光本质的信息。
) The similarity of the emission properties of macrocrystalline ZnO and nanocrystalline ZnO particles suggests that the origin of the visible emission is the same for all forms of ZnO. （粗晶体和纳米晶体氧化锌粒子发光性能的相似性意味着，所有形态下的氧化锌的可见发光起因是相同的。
）However, the kinetics involved in the emission processes are expected to be very different for them. (但在发光过程中所涉及的动力学机理被认为是迥然不同的。
)3. Conclusion (结论)Steady-state luminescence measurements were performed on suspensions in 2-propanol of nanocrystalline ZnO particles of different sizes. (稳态发光测量是在粒径大小不同的氧化锌纳米晶体的2-丙醇悬浮液中进行。
)All suspensions show two emission bands: a relatively weak and sharp exciton emissionband and a more intense and broad trap emission band in the visible part of the spectrum. (所有悬浮液都呈现两个发光带：一个是较弱且狭窄的激子发光带，另一个是在可见光谱内的较强较宽的诱捕发光带。
)A model for the kinetics of the radiative and non-radiative processes in nanocrystalline ZnO particles is proposed, based onthe assignment of the visible emission to a recombination of a shallowly trapped electron with a deeply trapped hole. (提出了关于氧化锌纳米晶体粒子内的辐射性及非辐射性的动力学机理的模型，该模型基于可见发光是浅陷阱俘获电子与深陷阱空穴的复合。
) From the particle size dependence of the emission properties it is concluded that the photogenerated hole is trapped at a surface system (probably O2-/O-). (从发光性能的粒子尺寸依赖性，可以得出这样的结论，光致空穴俘获于表面体系（很可能是O2-/O-）。