Preparation And Characterization Of Lead Sulfide And Cadmium Sulfide Nanocrystals

Lead sulfide (PbS) is an important semiconductor material with a small bandgap (0.41eV) and large exciton Bohr radius (18nm). It is promising in the applications in the fields of nonlinear optics, IR detectors, displaying devices and solar cell. It can be used to be prepared to PbS nanoparticle based-DNA probes to detect and identify DNA fragments. Cadmium sulfide (CdS), an intrinsic semiconductor in of IIB-VIA group with a large bandgap (3. 6eV) and a direct transition band structure, is widely used in the field of solar energy conversion, nonlinear optics, actinochemistry battery and photo catalysis. Thus, it is of interests to carry out studies on PbS and CdS nanomaterials.Three methods were used to prepare PbS nanoparticles. Some test methods such as XRD, TEM, absorption spectra and PL were used to analyze these nanoparticles. And CdS nanomaterials and PbS/CdS composite materials were prepared through the in-situ source-template-interface reaction route.Lead nitrate was used as lead source, carbon disulfide as sulfur source, carbon disulfide and ethylene diamine as dripping shuttering, and PbS was in situ synthesized at the CS₂-H₂O interface via the in-situ source-template-interface reaction route. The result of TEM observation presents that the diameter of PbS nanoparticles are about 60nm; the result of XRD analysis shows that the PbS nanoparticles are of face-centered cubic in structure; the result of optical absorbance measurement presents that exciton absorption peaks appear at 1680nm and 1731nm, with blue shift compared with bulk PbS due to the quantum confinement effect; the result of PL measurement shows that fluorescence emission peaks appear at 1328nm and 1516nm under green laser light excitation at 532nm. Lead nitrate was used as lead source, both thioacetamide and thiocarbamide as sulfur source and stabilizer, and PbS nanoparticles were prepared by using the sonochemistry method. The result of TEM observation presents that the PbS nanocrystals are of cubic structure; the peak in the XRD profile is relative sharp, which demonstrating that the crystal is in a good crystalline state; the result of optical absorbance measurement presents that exciton absorption peaks appear at 1675nm and 1728nm, with obvious blue shift; the result of PL measurement shows that fluorescence emission peak appears at 1641nm under green laser light excitation at 532nm. Lead nitrate was used as lead source, polyvinylpyrrolidone as stabilizer, S was reduced with potassium borohydride, and PbS nanorods were prepared at room temperature. The result of TEM observation presents that the diameter of the PbS nanorods are about 200nm, and the electron diffraction pattern analysis demonstrats that the PbS nanorods are single crystal structure; the result of XRD analysis presents that this PbS nanorods are of face-centered cubic structure and that the strong and sharp peaks indicate that PbS dendrites are highly crystalline.CdS nanomaterials and PbS/CdS composite materials were prepared through the in-situ source-template-interface reaction route. The result of TEM observation shows that the out diameter of the hollow structure is about 40～60nm; the result of XRD analysis indicates that the crystal structure of CdS is hexagonal; the absorption onset wavelength of the CdS shifts blue obviously compared with the bulk CdS due to the quantum confinement effect; the result of PL measurement shows that fluorescence emission peak appears at 470nm under green laser light excitation at 213nm. Diffraction peaks of the CdS and PbS nanocrystals can be found in there XRD profiles of the PbS/CdS composite materials, and the CdS is of hexagonal structure and the PbS is of face-centered cubic structure; the absorption spectrum profiles indicate that the absorption band is rather wide, ranging from 200nm to 1800nm.