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Luminescent and colorimetric properties of silica-coated spherical cadmium telluride nanocrystals in an external electric field

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The study concerns the behavior of optical and colorimetric properties of cadmium telluride semiconductor colloidal quantum dots covered with silica shell (CdTe/SiO2, core/shell) in an external constant electric field has been studied. To date, the electric field is known to lead mainly to quenching and red shift of the luminescence spectra of quantum dots; however, in most of the corresponding studies only the behavior of band-edge luminescence is considered. In this work, in addition to the luminescence due to interband transitions, the effect of the electric field on the trap-related luminescences of core/shell quantum dots is studied. Semiconductor nanocrystals were synthesized by colloidal chemistry methods. The product mixture was a solution of quantum dots in an aqueous medium. To investigate the optical properties of CdTe/SiO2 nanoparticles in an external electric field, a series of samples was fabricated on the basis of an optically passive cellulose film, in the pores of which quantum dots were embedded. The final sample was a cellulose film with quantum dots sandwiched between two glasses with transparent indium tin oxide electrodes. The strength of the constant electric field applied to such structures reached 140 kV/cm. Photoluminescence spectra of the investigated nanostructures were recorded using a CCD spectrometer. As a result of the experiments it was found that the presence and subsequent increase of the external electric field leads to quenching of the intensity of both band-edge and traprelated photoluminescence of quantum dots. This fact is associated with a decrease in the overlap between electron and hole wave functions under the action of the electric field. It is also shown that at moderate field strength there is a slight increase in the total photoluminescence intensity. This observation can be related to impeded charge carrier trapping. The demonstrated quenching of luminescence intensity is also consistent with the results of other authors who have shown a decrease in the absorption of quantum dots in external electric fields. The stability of colorimetric characteristics of the spherical nanoparticles in an external electric field has been demonstrated. The results of the study can be used for development of optoelectronic devices based on CdTe/SiO2 nanoparticles. 

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