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

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

Lithium tetraborate co-doping with transition and alkali metals

Luminescent properties of tissue-equivalent detectors have been studied. The detectors are made of lithium tetraborate and doped with magnesium, manganese, or tin. Analysis of the results obtained makes it possible to confirm the complexity of luminescence centers in lithium tetraborate without using structural analysis methods. For the first time, the effect of the method and order of introducing impurities on the storage properties of the studied materials was demonstrated and explained. The synthesis of the lithium tetraborate host occurred through the reaction of H3BO3 and Li2CO3. The binding agent was SiO2. Magnesium, manganese, or tin dopants were introduced during the synthesis of the host or later. The final stage of the synthesis was pressing of the powder into tablets and sintering in argon at 1158 K. The photoluminescence and pulsed cathodoluminescence signals were recorded by CCD-spectrometers. Portable pulsed electron accelerator was used for excitation of cathodoluminescence. Thermally stimulated luminescence was recorded by a special dosimetric reader with a heater and photo muliplier tube after exposure of the samples to an electron beam. Photoluminescence spectra, cathodoluminescence spectra, and glow curves were obtained for five samples of lithium tetraborate with various impurities, namely, magnesium, manganese, and tin. A comparison of the results was made to identify how the intensity signals depend on the amount of impurities and order of their introduction. It was found that the synthesis procedure and the order of introducing the dopants affect the luminescent properties of the materials. It has been suggested that the impurities take different positions in the lithium tetraborate structure. Predominant introduction of a particular impurity at a particular site leads to the following result. Doping with tin provides an increase in the number of luminescence centers of manganese and significantly sensitizes its luminescence, while doping with magnesium leads to the opposite result. The results indicate that it is possible to create advanced tissue-equivalent detectors with tailored luminescent. Depending on the dose of ionizing radiation, the use of material with different sensitivity and radiation resistance is required. Thus, the production of detectors based on lithium tetraborate and the described impurities in the future will give an opportunity to create a promising group of ionizing radiation detectors with various properties

Comparative analysis of parameters of pulsed copper vapour laser and known types of technological lasers

In the present paper we present the results of a comparative analysis of pulsed copper vapour lasers with visible emission wavelengths of 510.6 and 578.2 nm and pulse duration of 10-30 ns and known types of technological lasers as well as the prospects for using the copper vapor laser for microprocessing of material