Produce Core/Shell PbS/CdS Quantumdots And Surface Functionalization

PbS quantum dots (QDs) have tremendous capacity for applications ranging from bio-labeling to solar cells due to their efficient emission over a large spectral range in the infrared. However, these applications have been confined by unsteadiness in quantum yield and peak position on exposure to external environment. QDs with bright, stable, and wavelength-tunable luminescence are very promising emitters for various photonic and optoelectronic applications. Recently developed strategies for inorganic surface capping of colloidal NCs using metal chalcogenide complexes have opened new perspectives for their applications.However, these applications have been limited by instability in emission quantum yield and peak position on exposure to ambient conditions. An effective strategy to improve PbS QDs’stability is overgrowth with a shell of a more stable semiconductor, such as CdS, resulting in core/shell PbS/CdS QDs. The PbS/CdS QDs were fabricated in a two-step method. In the first step, PbS QDs with a4.8nm diameter were prepared by using organic metal. Second, PbS/CdS QDs with3.8nm PbS core and0.5nm CdS shell were fabricated by exposing PbS QDs in Cd2+solution for24h at65℃. In this article, cation exchange method was adopted to moderate reaction temperature in a low temperature, so that Ostwald ripening in high temperature was avoided.The results of transmission electron microscopy (TEM) and high resolution TEM showed that PbS QDs were sphere and in a cubic cystal without obvious lattice defects. After PbS QDs being cation exchanged, PbS/CdS QDs’size and crystalline form almost kept the same. The results of X-ray diffraction also showed both the crystalline form of PbS and PbS/CdS QDs were cubic. That PbS/CdS QDs had strong absorption and bright photo fluorescence in near infrared region was proved in UV/Vis/NIR and PL spectrum. The stability was proved by comparing fresh QDs’and3months later QDs’PL spectrum, in which little blue shift and decrease in PL intensity was found in PbS/CdS QDs. Besides, the results showed that the degree of cation exchange was limited on the surface of the QDs. For example,0.5nm CdS shell was formed on the surface of PbS QDs after being exchanged for24h in65℃. Thin as CdS shell was, it could effectively passivate PbS QDs’ surface defects and significantly improve the photooxidation stability. By employing cation exchange method, highly crystallized core/shell PbS/CdS QDs with superior and stable infrared emission were fabricated at a low temperature.Here we report an all-inorganic surface functionalization of highly luminescent NIR-emitting PbS/CdS QDs and studies of their luminescence properties. An effective approach to improve PbS QDs’ stability is growth with a shell of a more stable semiconductor, such as CdS, resulting in core/shell PbS/CdS QDs. We show that inorganic capping allows simple low-temperature encapsulation of inorganic QDs into a solution-cast IR-transparent amorphous As2S3matrix. The resulting all-inorganic thin films feature stable IR luminescence in the telecommunication wavelength region.