作　　者： ; ; ; ; ;

机构地区： 南京大学物理学院近代声学教育部重点实验室

出　　处： 《南京大学学报：数学半年刊》 1997年第1期32-36,共5页

摘　　要： 纳米钛酸镍粉末从可见光到近红外范围的光声光谱出现了三个强的吸收峰．445nm和505nm附近的吸收峰产生于自由激子和束缚激子的光跃迁，其变化趋势强烈地依赖于颗粒度大小，840nm处的吸收峰源于杂质的贡献。 The photoacoustic spectra of nanometer powder NiTiO 3 with different grain diameters are studied. The results show that three well-defined absorption peaks are observed in visible to near infrared wavelength range 350￣1200nm. Among them two peaks P 1 and P 2 are located at the short wavelength range around 445nm and 505nm, respectively. It is also shown that, as the decrease of the grain size, the blue shifts and the background increases of both peaks (P 1 and P 2) appear, as well as the peak P 2 widens and the sharp of the peak P 1 decreases. In addition, an absorption band with width about 200nm appears in red to near infrared range with an absorption maximum at 840nm. According to the analyses of the energy levels of the luminant titanutes, the free excitons and trapped excitions are responsible for the the peaks P 1 and P 2. But the absorption band around 840nm is from the dilute impuriies. An important property of the structures of nanoscaled materials is that the surface area occupies large pecentage relative to volume and a lot of electrons are located at surfaces. Because to the coordinations of the surface states are not perfective, there are much more holes, thus the probability of the recombination of the electrons and holes increase,which induces much more exciton density in nanoscaled materials than others. Meanwhile, a lot of defects appear in nanoscaled materials and the number and kinds of the defects increase with the reduction of the grain sizes. On the other hand, the trapped exciton increase makes the relative number of the free excitons decrease. The changes become more apparant with the size reduction, which induces the peak P 1 to be smooth. But due to the energy distribution of the trapped excitons in a wide range induced by the different kinds of defects the peak P 2 widens. Besides, the main reason of the blue shifts of peaks P 1 and P 2 is the energy gaps increase. On the other hand, there

关 键 词： 光声光谱 光吸收 纳米材料

领　　域： [机械工程] [理学] [理学]