Formation of Luminescence Centers in Oxygen-Deficient Cerium Oxide Nanocrystals

In this work the peculiarities of oxygen vacancies formation in cerium oxide nanoparticles for different external influences have been investigated by spectroscopic methods. The features of oxygen vacancies and therefore non-stoichiometric cerium oxide formation in CeO2 nanocrystals depending on the atmosphere of high temperature treatment were investigated. Stimulation of oxygen vacancies formation in reducing and neutral atmospheres was revealed. Occurrence of two different luminescence centers (viz. the charge-transfer complexes formed by Ce4+ and O2- ions, and Ce3+ ions stabilized by vacancies) after cerium oxide nanoparticles annealing in a neutral atmosphere has been observed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3544

Suppression of impurity ions optical transitions dephasing in nanocrystals

Abnormally narrow spectral lines have been observed in the luminescence spectra of Y₂SiO₅Pr³⁺ and YVO₄:Eu³⁺ nanocrystals at the room temperature. This fact was interpreted as the result of optical transitions dephasing processes suppression in the nanocrystals. The general cause of the observed effect is the weakening of phonon scattering on the impurity centre as a result of the quantum size effect in nanocrystal phonon subsystem. At first the dependence of spectral line width on the nanocrystal size has been shown. Unnecessary of the deep cooling for narrow optical resonances obtaining makes these nanocrystals a potential candidate for the wide set of applications in the optical memory and quantum computing devices.На спектрах люмінесценції нанокристалів Y₂SiO₅Pr³⁺ та YVO₄:Eu³⁺ за кімнатної температури спостерігалася наявність аномально вузьких спектральних ліній. Це було інтерпретовано як результат заглушення процесів дефазування оптичних переходів у нанокристалах. Причиною зазначеного ефекту є ослаблення розсіювання фононів на домішковому центрі внаслідок впливу квантово-розмірного ефекту на підсистему фононів у нанокристалі. Уперше отримано залежність ширини спектральних ліній від розміру нанокристала. Відсутність потреби глибокого заморожування для отримання вузьких оптичних резонансів відкриває можливості використання таких нанокристалів для створення пристроїв оптичної памяті та квантових компютерів.На спектрах люминесценции нанокристаллов Y₂SiO₅Pr³⁺ и YVO₄:Eu³⁺ при комнатной температуре наблюдалось наличие аномально узких спектральных линий. Это было интерпретировано как результат подавления процессов дефазировки оптических переходов в нанокристаллах. Причиной наблюдаемого эффекта является ослабление рассеяния фононов на примесном центре в результате влияния квантово-размерного эффекта на подсистему фононов в нанокристалле. Впервые получена зависимость ширины спектральных линий от размера нанокристалла. Отсутствие необходимости глубокого замораживания для получения узких оптических резонансов открывает широкие возможности применения данных нанокристаллов для создания устройств оптической памяти и квантовых компьютеров

Formation of luminescent centers in CeO2CeO{_2} nanocrystals

The nature of luminescence centers in CeO2 nanocrystals with varied oxygen stoichiometry has been investigated. It was shown that the luminescence of CeO2 is caused by the radiative relaxation in two different optical centers: the first one is Ce4+–O2− charge transfer state and the second one is Ce3+ ions. The ratio of Ce4+/Ce3+ centers depends on the amount of oxygen vacancies, therefore the variation of ceria stoichiometry allows changing the concentration of Ce4+–O2− and Ce3+ luminescence centers. Analysis of splitting of the excitation bands of Ce3+ luminescence has shown that oxygen vacancies in CeO2 nanocrystals are formed at the nearest-neighbor position to the cerium ion

Newly synthesized carbocyanine fluorescent probes, their characteristics and behavior in proliferating cultures

Aim. To study possibile application of C2, C9, C18 and JC-1 carbocyanine fluorescent dyes for cell culture characterization. Methods. Morphological methods, fluorescence-activated cell sorting (FACS) analysis, luminescent microscopy were used. Results. The studied carbocyanine probes were shown to be preserved in dividing cells for at least 4 duplications. It was found that carbocyanine probe JC-1 did not transit from cell to cell under combined culturing of labeled and non-labeled cells. Conclusions. The paper covers the use of carbocyanine fluorescent probes for long-term culturing of cell lines. Probes C9 and JC-1 were optimal for the proliferative culture observation, allowing to trace mitochondrial functional stat

Spectroscopic Properties of Nanoceria Allowing Visualization of Its Antioxidant Action

Two distinct luminescence centers were revealed in ceria nanocrystals: first one – Ce3+ ions with 5d-4f luminescence at 390 nm, and second one – Ce4+–O2− complexes showing charge transfer (CT) luminescence at 630 nm. Intensity of Ce3+ luminescence depends directly on the concentration of oxygen vacancies in nanoceria and can be varied by means of change of both heat treatment atmosphere from oxidizing to reducing and the size of nanocrystal. Ce3+ luminescence can be used for visualization of the processes of interaction between ceria nanoparticles and reactive oxygen species using relative intensity of Ce3+ band as a measure of Ce4+/Ce3+ ratio during oxidation reaction.

Luminescent properties of composite scintillators based on PPO and o-POPOP doped SiO2\mathrm{SiO_2} xerogel matrices

New composite scintillation detectors were obtained by incorporation of PPO and o-POPOP organicscintillators into porous sol–gel silica matrices. Composites possess high photoluminescence intensityand decay time in nanosecond range. The absolute light yield of composite scintillators at excitation byalpha-radiation is about 4000–5000 photons/MeV and the pulse–height resolution is about 30%. The investigations of time-resolved luminescence of composites performed under excitation by synchrotron radiation in the 3.7–25 eV range have shown that the non-radiative energy transfer between host matrix and dopant molecules occurs via singlet states of SiO$_2$ oxygen-deficient centers

Spectral-luminescent properties of derivatives of squaraine probes at interaction with the isolated rat liver cells

Aim. To find out approaches for studying cellular functional state using new fluorescent squaraine probes. Methods. Dependence of fluorescence parameters of squaraine and polymethine dyes on the properties of their microenvironment in biomembranes was studied by microspectrofluorimetry. The quantitative microfluorimetry of single cells was applied for the evaluation of probes accumulation in cells and for investigation of dynamics of dyes photobleaching. Results. The data obtained evidence that a chromophoric part of the squaraine dyes molecules is mainly localized in a more polar microenvironment in biomembranes, as compared to the cationic polymethine probes. Conclusions. Chromophore of anionic squaraine probe in native membranes is located in the upper membrane layer in the region of polar phospholipids heads, while the cationic probes can penetrate deeper into the membrane. The anionic squaraine probe SqSC4 was determined as the most photostable dye among the investigated probes

A large acceptance lead-scintillator time-of-flight wall for neutral and charged particles

A large acceptance lead-scintillator time-of-flight (TOF) wall has been developed to detect photons, neutrons, and charged particles produced in meson-photoproduction experiments on the proton and on the neutron. A TOF resolution of 600 ps and a position resolution of 11 x 18 cm(2) (full-width at half-maximum) have been achieved. The wall has been successfully used in eta and pi(+) photoproduction experiments as a photon and a neutron detector. This paper reports its design, calibration and performance. (C) 2002 Elsevier Science B.V. All rights reserved