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11/14/05

Optical and structural properties of PbS nanoparticles produced in Zeolite Na-X



Electron diffraction pattern of PbS nanoparticles in zeolite X

The study of semiconductor nanoparticles embedded in a matrix is currently a very active research area. These small particles have physicochemical properties quite different from those in the bulk material. A great variety of semiconductors nanoparticles have been synthesized in different matrix such as polymers, glasses and zeolites with the main purpose to modify their properties by controlling the particle size. Alterations to these properties mean they can be tailored to specific applications in the fields of non-linear optics, photovoltaic conversion, catalysis, optoelectronics, etc.

In this work, published in AZojomo*, by M. Flores-Acosta, R. Pérez-Salas, M. Sotelo-Lerma, F. F. Castillón-Barraza and R. Ramírez-Bon from Unidad Querétaro, Universidad de Sonora and Universidad Nacional Autónoma de México, PbS nanoparticles were synthesized in zeolite Na-X by means of ionic exchange processes in alkaline aqueous solutions. They reported the optical and structural properties of the system PbS-Na-X zeolite.

The 4.0nm PbS nanoparticles have spherical shape, the crystalline structure of galena and are embedded uniformly in the zeolite matrix. The 1se-1ph and 1pe-1ph excitonic transitions observed in the absorption spectra of the PbS-Na-X system is explained in terms of the crystalline quality of the PbS nanoparticles.

The results show that spherical PbS nanoparticles are formed not inside the zeolite cages but outside, embedded in the zeolite matrix. The absorption spectra of the samples display exciton absorption bands at much higher energy than the fundamental absorption edge of bulk PbS. This result is a consequence of strong quantum confinement effects produced by the reduced size of the PbS nanoparticles as compared to the exciton Bohr diameter of bulk PbS.

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