Кафедра фізико-математичних наук
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Browsing Кафедра фізико-математичних наук by Author "Khomenkova, Larysa"
Item Optical properties of Zn0.75Mg0.25O:Mn ceramics(2023) Markevich, I.; Korsunska, N.; Stara, T.; Polishchuk, Yu.; Vorona, I.; Kozoriz, K.; Ponomaryov, S.; Melnichuk, O.; Melnichuk, L.; Cremades, A.; Khomenkova, LarysaMn-doped ZnO, MgO and Zn0.75Mg0.25O samples ([Mn] = 0.1 at.%) were produced by conventional solid-state technique and investigated by means of XRD, EPR, absorption, photocurrent, photo- and cathodoluminescence methods. It was shown that Zn0.75Mg0.25O solid solution with hexagonal structure has the bandgap of Eg ~3.65 eV. The quenching of host defect-related luminescence in ZnO:Mn and in hexagonal Zn0.75Mg0.25O:Mn was observed, while the Mn-related emission being absent. The energy level of Mn2Z+n center in hexagonal Zn0.75Mg0.25O:Mn was found to be at 2.16 eV below conduction band (c-band) bottom and all excited states of Mn2Z+n ions, including the lowest one, reside in c-band, as it takes place in ZnO:Mn. It is concluded that the necessary condition to obtain Mn-related light emission in Mn-doped alloys is to make deeper the lowest excited level of Mn2Z+n ions. One of the solutions is to produce Zn1-xMgxO:Mn solid solution with the bandgap energy larger than 4.0 eV using nonequilibrium fabrication approaches.Item Peculiarities of photoluminescence excitation in ZnO ceramics doped with group-I elements(2022) Korsunska, N.; Markevich, I.; Stara, T.; Kozoriz, K.; Melnichuk, L.; Melnichuk, O.; Khomenkova, LarysaExtrinsic luminescence, excitation, and absorption spectra of ZnO ceramics doped with acceptors (lithium, copper, or silver), as well as undoped ZnO ceramics sintered in various atmospheres, have been studied. It is shown that the acceptor doping leads to the appearance of luminescence bands in the visible spectral interval, and their intensity significantly exceeds the intensity of the corresponding emission from undoped specimens. A selective maximum at 390–400 nm, which is usually absent in the excitation spectra of self-activated luminescence bands in undoped ZnO specimens, is found to dominate in the excitation spectra of those bands. It is supposed to be caused by the interaction between the emitting centers and defects arising near the impurities, with the Auger process being the most probable mechanism of energy transfer from these defects to the emitting centers. By sintering ZnO ceramics in the presence of carbon, it is shown that the appearance of the selective maximum in the excitation spectra occurs due to the extraction of oxygen from ZnO ceramics. An assumption has been done concerning the nature of the centers responsible for the excitation of extrinsic luminescence.Item Two excitation pathways of Pr3+ ion emission in HfO2:Si:Pr films depending on crystalline phase transformations in annealing(2023) Garcia Andrade, Maria Alejandra; Torchynska, T.; Casas Espinola, Jose Luis; Vel´azquez Lozada, E.; Polupan, G.; Khomenkova, Larysa; Gourbilleau, F.The impact of annealing on the emission and transformation of the crystalline phases in Si rich HfO2:Pr films was investigated by analyzing the morphology, chemical composition, structure, and photoluminescence (PL) characteristics. Films were prepared by RF magnetron sputtering and monitored as-prepared and after annealing at 1000 ◦C for 5–60 min. Emission through host HfO2 defects has only been detected in spectra of as-prepared Si rich HfO2:Pr films. Heat treatment for 30 min stimulates a phase transformation together with the appearance of a tetragonal HfO2 phase and Si quantum dot (QDs). This last process is accompanied by appearance of bright emission of rare earth (RE) ions Pr3+ related to the transitions in the 4f energy levels. Additional annealing for 60 min stimulates the complete oxidation of the Si QDs with the formation of the SiO2 phase along with partial destruction of a tetragonal HfO2 phase. This last process is accompanied by the significant increase of the intensity of Pr3+ ion emission. Two forms of luminescence excitation in 4f energy levels of Pr3+ ions are discussed, related to energy transfer to Pr3+ ions, first from Si QDs and then from host defects in HfO2. These changes in the excitation pathways of Pr3+ ion emissions are stimulated by the transformations of the crystalline phases in the thermal treatment together with the generation of host HfO2 defects. Hafnia-based materials doped with RE elements are interesting for telecommunication technology and applications in waveguides and optoelectronic devices.