| This thesis is mainly focusing on the activation and quenching effects of Zn2+ and Mn2+ introduction into the colloidal ZnS:Mn2+ nanocrystals respectively. The activation effect of Zn2+ modification, including enhancement of emission intensity, slowing of luminescence decay and increasing of quantum yields, results from the formation of ZnS shell outside the nanoparticles, which is passivating the surface of nanoparticles, eliminating the surface quenching centers, so as to block the nonradiative transition pathways through these kind of quenching centers. These quenching centers can quench both blue emission related to the surface defects and the orange emission of Mn2+ impurities. They are most likely originated from the dangling bonds of the lone pairs on surface S2' or the Zn2+ vacancies. The dynamic analysis of this activation process is presented on the basis of Langmuir isotherm model.The quenching centers aroused by Mn2+ introduction merely quench the orange emission of colloidal ZnS:Mn2+ nanocrystals. The quenching process of this kind of quenching centers, which reduce the energy of 4T1 level rather than that of conduction band, is different from that of the quenching centers eliminated by Zn2+ introduction. The quenching data is analyzed considering the distribution of Mn2+ additives adsorbed at the surface of colloidal nanoparticles. These quenching centers are most probably the Mn2+ themselves, which can from Mn-Mn pairs so as to perform the energy migration from the interior Mn2+ to the Mn2+ adsorbed on the surface. This indicates that rich Zn2+ and poor Mn2+ ions in the colloidal solution of ZnS:Mn2+ NPs is the key to obtain highly efficient luminescence and highly quantum yields. The research on the properties of surface modification may be helpful to the widely application of nano-sized materials in the future. |
