The Effect of Lateral Size and Surface Passivation on the Near Band Edge Excitonic Emission from Quasi Two-Dimensional CdSe Nanoplatelets

As a new type of quasi two-dimensional nanomaterial, CdSe nanoplatelets (NPLs) possess excellent properties such as narrow emission peak, large absorption cross-section and low threshold of amplified spontaneous emission. However, the origin of emission especially at low temperature has not been studied clearly up till now. Here we study the temperature dependent photoluminescence of CdSe NPLs which show two emission peaks at low temperature. It is interesting to note that the intensity of the low energy peak shows a correlation with laser irradiation time. Moreover, the low temperature PL spectra of four CdSe NPLs with different lateral sizes demonstrate the relationship of low energy peaks with the surface. It has been confirmed that CdSe NPLs with larger surface areas to volume ratio have stronger low energy emission, which is ascribed to the surface state related emission. Finally, surface passivation of CdSe NPLs attenuates the intensity of the low energy peak, which further verifies our model. Our r...