Yu. Yu. Bacherikov

Role of paramagnetic defects in light emission processes in Y-doped ZrO2 nanopowders

Luminescence and structural properties of pure and Y-doped ZrO2 nanopowders with different Y content synthesized by co-precipitation of Zr and Y salts were investigated by x-ray diffraction, transmission electron microscopy, electron paramagnetic resonance (EPR) and photoluminescence (PL) methods. It was found that at constant calcination temperature (700 °С), the increase of Y content stimulates the transformation of crystalline phase from monoclinic through the tetragonal to the cubic one. Generally, room temperature PL emission was found to be similar for the samples with different Y content, demonstrating the same overlapped PL components in visible spectral range under extrinsic excitation. The relative contribution of each PL component was found to be affected by calcination time. In EPR spectra of as-prepared samples no signals were observed. The annealing in N2 or H2 flow results in the appearance of the signal from surface Zr3+ defects. In the latter the signal assigned to F-center also arises. The anti-correlation observed between the PL intensity and the value of the Zr3+ EPR signal allows us to conclude that the Zr3+ center is the center of fast non-radiative recombination. At the same time, interrelation between the intensity of the EPR signal assigned to F-centers and observed PL bands was not found.

Thermal transformations in ZnS in the course of doping with CuCl

The photoluminescence, electroluminescence, and electron paramagnetic resonance spectra of ZnS powders thermally doped with CuCl are investigated. The processes occurring in the material during simultaneous annealing of ZnS and CuCl are discussed, and the influence of the annealing conditions on the formation of the CuS and Cu2S phases in zinc sulfide is analyzed. It is shown that the concentration ratio of the blue luminescence centers to the green luminescence centers and the concentration of Mn2+ paramagnetic centers in the phosphor prepared can be controlled by varying the rate of heating of the material to the annealing temperature. A technique based on low-temperature annealing is conceptualized and developed for synthesizing materials that, as rule, can be produced only through high-temperature annealing.

Morphology and optical properties of titanium-doped porous silicon carbide layers

The effect of rapid thermal annealing (RTA) in oxygen on the properties of titanium-doped porous silicon carbide (por-SiC) layers has been studied. The data on the surface morphology and the photoluminescence (PL) spectra show that the high-temperature diffusion annealing is accompanied by the formation of titanium silicides, by an increase in the grain size of the material, and by the emergence of pores on the surface of the por-SiC-Ti sample. The results of PL measurements are consistent with data on the phase composition and the surface morphology of the samples. It is established that RTA leads to modification of the titanium-doped por-SiC structure.

Effect of microwave annealing on silicon dioxide/silicon carbide structures

The methods of atomic force microscopy and optical absorption spectroscopy are applied to study the effect of microwave treatment on the properties of SiO2/SiC structures obtained by rapid thermal annealing and conventional thermal oxidation in steam. From the variation of the sample optical density with total time of microwave treatment, it is concluded that the structures prepared by rapid thermal annealing are more stable against microwave radiation. It is shown that long-term microwave treatment flattens the oxide film surface at the nanolevel regardless of the method of silicon carbide oxidation.

Characterization of porous silicon carbide according to absorption and photoluminescence spectra

The results of the atomic-force microscopy, optical-absorption spectroscopy, and photoluminescence spectroscopy of porous silicon carbide (por-SiC) produced by anodic etching are reported. Analysis of the data shows that the cubic SiC phase is lacking in the porous layer and the photoluminescence signal from por-SiC at the excitation photon energy hνex ≤ Eg appears due to the formation of radiative centers associated with impurity atoms and surface defects produced upon anodic etching of the sample and subsequent treatment to uncover the pores.

Features of ZnS-powder doping with a Mn impurity during synthesis and subsequent annealing

Luminescence, electron spin resonance, and X-ray diffraction (XRD) methods were used to investigate the features of ZnS-powder doped by Mn impurity during self-propagating high-temperature synthesis and subsequent annealing. The obtained powder consists of ZnS microcrystals with mainly hexagonal phase (80 ± 5)%. It was found, that after synthesis Mn presents not only in the form of non-uniformly distributed microscopic impurities in ZnS, but also in the form of Mn metal nanocrystals. Thermal annealing at 800°C leads to the additional doping of ZnS from metallic Mn, to the redistribution of the embedded Mn in the volume of microcrystals, and to the ZnS oxidation. At the same time, the ratio between the cubic and hexagonal phases does not change. It was shown that annealing causes a decrease in the concentration of the defects responsible for the luminescence-excitation bands, which correspond to transitions from the ground to the excited states of the Mn2+ ion. As a result of annealing, there is also a change in XRD coherent domain size. Simultaneously, the intensity of peaks in the luminescence-excitation spectrum with wavelengths of 375 and 395 nm was changed. The causes of these changes and the nature of the corresponding bands are discussed.

New insight on the interaction of self-activated and Mn-related emission centers in ZnS

The photoluminescence (PL) and PL excitation (PLE) spectra of undoped and thermally doped with Mn ZnS single crystals are studied. In the PL spectra, the bands caused by Mn-related and self-activated (SA) emission centers were observed. A number of narrow peaks whose intensity enhanced with increasing Mn content were found in the PLE spectra of SA emission. The same peaks were present in the PLE spectra of the Mn-related emission band. Some of these peaks were previously observed in the absorption spectra and attributed to Mn2+ ions. The appearance of Mn-related peaks in the PLE spectra of SA emission is explained by excitation transfer from the Mn2+ ions to SA emission centers. The conditions required for this transfer and possible mechanisms of the process are discussed.

Influence of the rate of increase in the induction on the spectral characteristics of luminescence of ZnS: Mn under treatment in a magnetic field

AbstractThis paper reports on the results of the investigation of photoluminescence and luminescence excitation spectra of a ZnS powder thermally doped with MnCl · 4H2O or MnS and subjected to a series of treatments in a pulsed magnetic field with the same maximum amplitude of the magnetic field induction (Bmax = 0.3 T) but with different rates of its increase

Luminescence from thermally doped nanopowders of zirconia

\dot B