Local Cathodoluminescence Research Articles

Сенсибилизация ионов европия (Eu-=SUP=-3+-=/SUP=-) тербием (Tb-=SUP=-3+-=/SUP=-) в керамике на основе кубического диоксида циркония, стабилизированного иттрием

In this work, stabilized f-ZrO2 ceramic samples with the compositions of (Zr0.82Y0.09Eu0.09)O1.91), (Zr0.82Y0.09Tb0.09)O1.91) and (Zr0.82Y0.09Eu0.045Tb0.045)O1.91 were studied. The elemental composition was studied by electron probe microanalysis, and the luminescent properties were studied by local cathodoluminescence (CL). An analysis of the Eu3+ CL spectra confirmed the stabilization of the cubic phase in ceramics at room temperature. The study of the obtained CL spectra, the 5D4-7F5 Tb3+ band luminescence decay kinetics, CL images and excitation spectra showed europium sensitization by terbium in (Zr0.82Y0.09Eu0.045Tb0.045)O1.91.

Sensitization of europium (Eu-=SUP=-3+-=/SUP=-) ions by terbium (Tb-=SUP=-3+-=/SUP=-) in ceramics based on yttrium stabilized cubic zirconium dioxide

In this work, stabilized f-ZrO2 ceramic samples with the compositions of (Zr0.82Y0.09Eu0.09)O1.91, (Zr0.82Y0.09Tb0.09)O1.91 and (Zr0.82Y0.09Eu0.045Tb0.045)O1.91 were studied. The elemental composition was studied by electron probe microanalysis, and the luminescent properties were studied by local cathodoluminescence (CL). An analysis of the Eu3+ CL spectra confirmed the stabilization of the cubic phase in ceramics at room temperature. The study of the obtained CL spectra, the 5D4-7F5Tb3+ band luminescence decay kinetics, CL images and excitation spectra showed europium sensitization by terbium in (Zr0.82Y0.09Eu0.045Tb0.045)O1.91. Keywords: f-ZrO2, Eu3+, Tb3+, Ceramics, Sensitization, Cathodoluminescence

Low-Temperature Synthesis of Glass-Ceramics with YNbO-=SUB=-4-=/SUB=- : Tb-=SUP=-3+-=/SUP=- Crystallites

The main aim of this work was to perform low-temperature synthesis of glass-ceramics with YNbO4 : Tb3+ crystalline inclusions and study the structural and luminescent properties of the samples synthesized. In the framework of this work, inclusions crystallized in the system B2O5-Na2O-Y2O3 -Nb2O5-Tb4O7 (Bura). It was shown that in this system, regardless of the precursors in the samples, YNbO4 : Tb3+ in an amount of more than 70% of the total crystalline component. The most promising system for the synthesis of activated glass-ceramics with YNbO4 proved to be synthesized from oxide precursors; it crystallized more than 95% YNbO4 : Tb3+ of the total crystalline component. The luminescent properties of crystalline inclusions were studied using the local cathodoluminescence method. The composition and structure of glass ceramics were studied by methods X-ray spectral microanalysis and X-ray diffraction phase analysis. Keywords: YNbO4 : Tb3+, luminescence, glass-ceramics.

Study of Glass Ceramics with YNbO-=SUB=-4-=/SUB=- : Tb-=SUP=-3+-=/SUP=- Crystallites Synthesized at Different Temperatures

The optimal temperature regime for the synthesis of glass ceramics with YNbO4 : Tb3+ crystalline inclusions has been established. Glass ceramics were synthesized on the basis of a sodium borate matrix from oxide precursors. It has been established that synthesis at a temperature of 950oC is optimal, since at this temperature only one crystalline phase YNbO4 : Tb3+ is formed in the glass and its content is maximum. The spectra of crystalline inclusions and the glass matrix were obtained by the method of local cathodoluminescence, the phase composition of glass ceramics was studied by X-ray phase analysis. Keywords: YNbO4, luminescence, terbium ion, glass ceramics.

Luminescence features of bulk crystals β-(Ga-=SUB=-x-=/SUB=-Al-=SUB=-1-x-=/SUB=-)-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

This work is devoted to the study of the luminescence inhomogeneity nature of bulk (GaxAl1-x)2O3 samples grown by the Czochralski method. In the study of sample cleavages by the local cathodoluminescence method, regions with different luminescence were observed. To determine the cathodoluminescence contrast nature, we studied the uniformity of the aluminum distribution, the surface topography, and compared the luminescence spectra and the kinetics of emission bands for different regions of the sample. Also, to determine the luminescence bands nature, the crystal was annealed in air at 1000oC. This made it possible to observe the change in luminescence for the same region of the sample. Based on the studies performed, it was concluded that inhomogeneous luminescence is associated with the distribution of point defects. Upon annealing in air, the transformation of nonradiative recombination centers into luminescent centers was observed. Keywords: gallium oxide, luminescence, point defects.

Исследование стеклокерамики с кристаллитами YNbO-=SUB=-4-=/SUB=- : Tb-=SUP=-3+-=/SUP=-, синтезированной при разных температурах

The optimal temperature regime for the synthesis of glass ceramics with YNbO4 : Tb3+ crystalline inclusions has been established. Glass ceramics were synthesized on the basis of a sodium borate matrix from oxide precursors. It has been established that synthesis at a temperature of 950°C is optimal, since at this temperature only one crystalline phase YNbO4 : Tb3+ is formed in the glass and its content is maximum. The spectra of crystalline inclusions and the glass matrix were obtained by the method of local cathodoluminescence, the phase composition of glass ceramics was studied by X-ray phase analysis.

Низкотемпературный синтез стеклокерамики с кристаллитами YNbO-=SUB=-4-=/SUB=- : Eu-=SUP=-3+-=/SUP=-

The main purpose of this work was to carry out a low-temperature synthesis of glass ceramics containing YNbO4:Eu3+ crystallites and to study the structural and luminescent properties of the obtained samples. Within the framework of this work, the inclusions that crystallized under the conditions of low-temperature synthesis in the systems of SiO2-Na2O-K2O-Y2O3-Nb2O5-Eu2O3 (SiNaK) and B2O5-Na2O-Y2O3-Nb2O5-Eu2O3 (BNa) were investigated for the first time. It was shown that YNbO4: Eu3+ crystallized in both considered systems. In the SiNaK system the crystallization of SiO2 also occurred (quartz, crisstabolite, and tridymite) under the selected conditions. The BNa system proved to be the most promising for the synthesis of activated glass-ceramics with YNbO4, since the required crystallites crystallized only in ithis system. The luminescent properties of crystalline inclusions were investigated using the local cathodoluminescence technique. The composition and structure of glass ceramics were studied by electron-probe microanalysis and X-ray diffraction phase analysis.

The study of gadolinium tantalum niobate (Gd(NbxTa1-x)O4) by local cathodoluminescence technique

In this work, the powder and ceramic samples of gadolinium tantalum niobate (Gd(NbxTa1-x)O4) grown by the liquid-phase method were studied. Phase homogeneity and composition were determined by x-ray diffraction analysis and electron probe microanalysis. Luminescent properties were studied by local cathodoluminescence technique. All samples obtained a high phase homogeneity. It was found that the dependence of the monoclinic lattice parameters on the niobium content in the niobium-tantalum pair has monotonic character. The solid solutions were formed at synthesis temperatures from 1180 to 1400°C. The sample of pure gadolinium niobate (GdNbO4) showed the maximal cathodoluminescence intensity.

Kinetic properties of YAG: Eu3+ emission upon electron beam excitation

Luminescent properties of yttrium-aluminum garnet activated by different amount of europium (YAG:Eu3+) single crystals were studied by local cathodoluminescence (CL) technique. Samples were grown by flux method. CL spectra were obtained in the range from 400 to 800 nm with spectral resolution of 0.1 nm. The rise and decay kinetics of various CL bands were investigated. The concentration dependencies of CL intensity and decay times of transitions were plotted. The concentration quenching for 5D1-7F2 Eu3+ transition was observed at about 3.5 at.% of Eu by Y, and for 5D2-7F1 and 5D3-7F3 transitions – at about 2.5–3 at.% of Eu by Y. For transition 5D0-7F1 no concentration quenching was observed. The high-energy excitation capture efficiency by different energy levels of Eu3+ in YAG was estimated based on the dependence of the CL rise rate of these levels on the electron beam current density. It was found that 5D1 energy level excitation capture efficiency is about three times higher than that of the 5D0, 5D2 and 5D3 energy levels.

Synthesis and Luminescent Properties of Gadolinium Tantalum Niobates Gd(NbxTa1 – x)O4

The feasibility of synthesizing gadolinium tantalum niobates by the liquid-phase method was demonstrated. The methods of X-ray diffraction, electron probe microanalysis, local cathodoluminescence, and photoluminescence were applied to study the samples. It was shown that under the selected synthesis conditions (T ~ 1400°C for 3 hours), no solid solution of niobium-tantalum was formed in the powder samples. When obtaining ceramic samples, it was possible to obtain a solid solution and to study the dependence of the luminescence intensity on the niobium content upon excitation of the samples by an electron beam. The maximum luminescence intensity was observed in the sample with the composition of GdNb0.9Ta0.1O4. It was shown that the inhomogeneity of luminescence is not related to fluctuations in composition, but is related to the inhomogeneous distribution of vacancy centers, which are luminescence centers.

Properties of Eu3+-doped zirconia ceramics synthesized under spherical shock waves and vacuum annealing

The work is dedicated to the study of the phase stability of (Zr, Hf, Y, Eu)Ox ceramics with the calculated formula Zr0.41Hf0.41Y0.09Eu0.09O1.91 synthesized by the co-precipitation method and subjected to detonation in spherical shock waves and vacuum annealing at 1700 °C. The phase composition of the starting precursor and ceramic samples was investigated by X-ray diffraction analysis. To analyze the local structure of samples, the method of rare-earth ion spectroscopy was applied with the use of the local cathodoluminescence technique. It was demonstrated that detonation in spherical shock waves leads to a decrease of residual monoclinic phase in ceramics, and vacuum annealing leads to its complete disappearance. The significant changes in the phase composition of ceramics after the impact of high temperature in vacuum and high pressure under spherical shock waves are not observed. Such materials can be used as stable matrices for actinide immobilization or advanced luminescence materials to be applied under extreme conditions.

Single peak deep ultraviolet emission and high internal quantum efficiency in AlGaN quantum wells grown on large miscut sapphire substrates

Deep ultraviolet (DUV) AlxGa1-xN/AlyGa1-yN-based multiple quantum wells (MQWs) were grown on sapphire substrates with miscut angles of 0.2° and 4°. Significantly reduced edge type dislocation density and in-plane anisotropy of dislocation distributions were demonstrated for MQWs grown on high miscut sapphire substrate. Up to 10-fold enhanced MQW emission was observed for MQWs grown on 4° miscut sapphire compared to that grown on 0.2° miscut sapphire, and internal quantum efficiency (IQE) as large as 88% was achieved. Compositional inhomogeneity and thus formation of potential minimum were ambiguously demonstrated by localized cathodoluminescence spectra across the step bunched surface of the MQW sample. However, from the macroscale point of view, single peak PL luminescence was shown for MQW grown on high miscut sapphire without peak separation, suggesting a strongly carrier localization effect. A three-dimensional atom diffusion and desorption model describing the MQW growth was also proposed. This work provides a promising approach towards the realization of highly-efficient DUV emitters.

Cathodoluminescence of TiO2 Films Formed by Molecular Layer Deposition

Use of the method of local cathodoluminescence in Si–TiO2 and Si–SiO2–TiO2 structures helps to elucidate the nature of centers influencing the operation of memristors. These measurements showed that electroforming leads to the appearance of luminescence in a 250–400 nm wavelength range in the external part of TiO2 layer characterized by high concentration of defects. This observation leads to a conclusion that a sharp interface is formed between dielectric layers of the structure, provides estimation of the absorption coefficient of TiO2 layer, and allows its bandgap width (~3.3 eV) to be evaluated for the oxide layers formed by the given technology.

Катодолюминесценция слоев TiO-=SUB=-2-=/SUB=-, полученных методом молекулярного наслаивания

AbstractUse of the method of local cathodoluminescence in Si–TiO_2 and Si–SiO_2–TiO_2 structures helps to elucidate the nature of centers influencing the operation of memristors. These measurements showed that electroforming leads to the appearance of luminescence in a 250–400 nm wavelength range in the external part of TiO_2 layer characterized by high concentration of defects. This observation leads to a conclusion that a sharp interface is formed between dielectric layers of the structure, provides estimation of the absorption coefficient of TiO_2 layer, and allows its bandgap width (~3.3 eV) to be evaluated for the oxide layers formed by the given technology.

Eu3+ As a Luminescent Probe for Studying the Structure of R2O3 Materials (R = Y, Eu, and Gd)

Spectra of Eu3+ in various dielectric matrices (Gd2O3:Eu3+, Y2O3:Eu3+, Eu2O3, and mSiO2/Gd2O3:Eu3+ mesoporous particles) are studied by local cathodoluminescence. The results allowed identification of the local environment of Er3+ ions in amorphous samples and detection of the monoclinic Eu2O3 phase impurity in samples with yttrium oxide. The cathodoluminescence spectra of chemically pure Y2O3, Eu2O3, and Gd2O3 are recorded. Conclusions about the structural features of the materials are made and confirmed by other methods (XRD and EPMA).

Non-destructive evaluation of depth, thickness and composition of single ZnCdSe nanolayers buried in II-VI heterostructures

Wide-gap ZnSe-based nanoheterostructures grown by molecular beam epitaxy are comprehensively studied by electron probe microanalysis and local cathodoluminescence techniques. These non-destructive methods applied in combination allow independent determination of true depth, composition, and thickness of single ZnCdSe nanolayers (NL), located deep inside the heterostructures, with a relative accuracy of 10%. The developed approach is based on the variation of the electron probe energy, which results in different thickness of the region where characteristic x-ray emission and cathodoluminescence occur. The former establishes relation between the NL depth and composition at a fixed NL thickness, as defined by using an original modelling program, while the latter connects the NL thickness and composition.

High-Temperature Annealing as a Method for the Silicon Nanoclusters Growth in Stoichiometric Silicon Dioxide

A method for the growth of nanocomposite layers in stoichiometric amorphous silicon dioxide is proposed. It is shown that, after annealing at a temperature of 1150°C in nitrogen atmosphere, a layer containing silicon nanoclusters is formed. Silicon nanoclusters have a crystal structure and a size of 3–6 nm. In a film grown on a n-type substrate, a layer of silicon nanoclusters with a thickness of about 10 nm is observed. In the case of a film grown on a p-type substrate, a nanocomposite layer with a thickness of about 100 nm is observed. The difference in the formation of a nanocomposite layer in films on various substrates is associated with the doping of silicon dioxide with impurities from the substrate during the growth of the film. The formation of the nanocomposite layer was confirmed by transmission electron microscopy, XPS and local cathodoluminescence studies.

Cathodoluminescence of YAG:Nd optical nanoceramics in the visible and UV ranges

Results of cathodoluminescence studies of optical YAG:Nd nanoceramics with different microstructure are presented. The composition of the samples was studied by the electron-probe microanalysis. The estimation of the average grain size was performed with the use of scanning electron microscopy and based on X-ray diffraction analysis. Local cathodoluminescence technique was used to collect the emission spectra and decays of emission in the UV and visible range. The “memory effect” in YAG:Nd nanoceramics luminescence was noticed and discussed. In particular, it was observed that the initial electron beam irradiation of sample leads to the increase of luminescence efficiency in the visible and UV ranges. It was confirmed also that the observed effect is long-lasting and remains for years. To understand the mechanism of the effect, the estimation of temperature annealing under continuous irradiation by electron beam was done. The model of memory effect involving trap states was proposed and discussed.

Study of the parameters of nanoscale layers in nanoheterostructures based on II–VI semiconductor compounds

Wide-gap ZnSe-based nanoheterostructures grown by molecular-beam epitaxy are studied by local cathodoluminescence and X-ray microanalysis. It is shown that the used methods allow nondestructive determination of the depth, elemental composition, and geometrical parameters of the nanoscale ZnCdSe layer. The accuracy of the results is verified by transmission electron microscopy. The research techniques are based on the possibility of varying the primary electron-beam energy, which results in changes in the regions of characteristic X-ray and cathodoluminescence generation.

Lifetime Measurements Well below the Optical Diffraction Limit

The dependence of excited electron–hole state properties on the size of their host semiconducting nanostructures is the seed for a plethora of applications such as light-emitting diodes (LEDs) and photovoltaic cells. However, the inability of state-of-the art, diffraction-limited optical techniques to probe lifetime variations at the scale of individual quantum emitters precludes the full understanding of the nanostructures’ optical properties. Here, we demonstrate the measurement of the individual lifetimes of quantum emitters a few angstroms thick separated by only a few nanometers, lifting the ambiguities usually faced by diffraction-limited techniques. This relies on the ability to monitor with subnanometer precision a fast electron beam that triggers extremely localized cathodoluminescence signals further analyzed through intensity interferometry (spatially resolved time-correlated cathodoluminescence, SRTC-CL). We demonstrate SRTC-CL to be a true nanometer counterpart of time-resolved photoluminesce...