Yu. V. Yermolayeva

Effect of the geometric shape of Lu2O3: Eu spherical nanocrystals on their spontaneous luminescence

Monodisperse red phosphor particles 100 nm in diameter with the Lu1.90Eu0.10O3 composition have been prepared using the developed technique for synthesizing spherical colloidal lutetium oxide particles with a size dispersion in the range 10–15%. The structure of spherical nanoparticles has been investigated, their excitation and photoluminescence spectra have been analyzed, and the lifetime of the 5D0 excited state of Eu3+ ions has been considered. It has been found that the luminescence decay time for spherical particles increases by a factor of 1.39 compared to that for a powdered phosphor Lu2O3: Eu (5 at %) prepared and treated under the same temperature conditions as the Lu2O3: Eu (5 at %) spherical particles. This effect has been associated with the change in the photonic local density of states in spherical optical cavities consisting of particles of the phosphor.

Change of the luminescence decay time for Lu2O3: Eu nanocrystals embedded in synthetic opal

The opal-Lu1.86Eu0.14O3 composites have been prepared using the developed technique for synthesizing luminophor nanocrystals in pores of synthetic opal through coprecipitation from a solution. It has been demonstrated that the position of the photonic stop band in the reflection spectrum of the infiltrated opal depends on the diameter of its spheres, the volume fraction of the embedded luminophor, and the angle of detection of the signal. The excitation and photoluminescence spectra of the composites have been analyzed, and the lifetime of the 5D0 excited state of Eu3+ ions has been examined. It has been revealed that the luminescence decay time for the luminophor increases by almost one order of magnitude with an increase in its content in opal pores. This effect has been attributed to the change in the nanocrystal size and to the decrease in the contribution from the surface nonradiative recombination in luminophor nanolayers of the composites.

Synthesis and optical properties of monodisperse spherical Y2O3-Eu+3 particles

Research has been done into the luminescent properties of spherical Y2O3-Eu+3 nanoparticles with average diameters from 70 nm to 400 nm and 15% size dispersion, which are obtained by bath synthesis. The spectral-time characteristics of the most intense red luminescence of europium (~611 nm) have been found to be dependent on nanosphere diameter, dopant concentration and optical pump power density. It is shown that the effects are related to the influence of surface nonradiative recombination and modification of the spontaneous emission rate in nanometer-scale dielectric solids.

Lasing in spherically shaped Y2O3-ZnO nanocomposites

The luminescence properties of spherically shaped Y2O3-ZnO nanocomposites with average diameters of 132 and 179 nm are studied. The nanocomposites are produced by synthesis from a solution, and their size dispersion is about 15%. Narrow peaks of lasing upon exciton radiative recombination in zinc oxide are observed in the ultraviolet spectral region. It is shown that, for small cavities (100–200 nm in diameter), individual nanospheres of the composite exhibit only one laser mode. The initiation of stimulated luminescence with a peak at 376 nm corresponding to the bound photon mode of nanocavities 179 nm in diameter is observed as the optical pumping power is increased to >130 kW cm−2.

Spontaneous and stimulated red luminescence of Lu2O3: Eu nanocrystals

The spectra of spontaneous and stimulated luminescence of Lu2O3: Eu (7 at %) nanopowders at different optical pumping intensities have been investigated. The obtained results—changes in the shape of the red luminescence spectra and in the lifetime of the 5D0 excited state of Eu3+ ions—indicate the onset of superluminescence with an increase in the excitation power. It has been found that an increase in the optical pumping intensity leads to a decrease in the luminescence decay time of the Lu2O3: Eu (7 at %) phosphor in the stimulated luminescence regime and to an increase in the quantum efficiency of red luminescence with a maximum at 611 nm.

Photoluminescence properties of core-shell SiO2/Lu2O3: Eu monodisperse heteronanoparticles

Core-shell monodisperse heteroparticles of the composition SiO2/Lu1.86Eu0.14O3 have been synthesized using the developed technique for preparing spherical colloidal silicon dioxide particles with the size dispersion in the range 2.0–2.5% and the procedure for producing nanocoatings on the surface of spheres by codeposition. The structure of heteroparticles has been investigated, their excitation and photoluminescence spectra have been analyzed, and the lifetime of the 5D0 excited state of Eu3+ ions has been examined. It has been revealed that the luminescence decay time for heteroparticles increases by a factor of approximately two compared to that for a powdered luminophor Lu2O3: Eu (7 at %) prepared and treated under the same temperature conditions as the SiO2/Lu2O3: Eu (7 at %) heteroparticles. This effect has been attributed to the change in the effective refractive index and the local density of photon states in luminophor nanolayers of heteroparticles.

Structure and morphology of spherical crystalline (Y1 − xEux)2O3 particles

The structure and morphology of monodisperse spherical particles of (Y1 − xEux)2O3 solid solutions prepared through the low-temperature thermolysis of an amorphous precursor under isothermal conditions (t = 800°C) have been analyzed in detail in relation to the particle size and composition. The results demonstrate that, in addition to having a polycrystalline (block) structure, the spherical (Y1 − xEux)2O3 particles are porous, with a mesoscopic residual pore size. Reducing the diameter of the spherical particles from 400 to 70 nm reduces their porosity and improves their structural perfection. The addition of Eu3+ cations stimulates the growth of crystalline blocks that form a spherical particle, activating diffusion processes in the cation sublattice of the solid solution.

Luminescence of Eu3+ rare-earth ions in Lu2O3 nanospheres

The kinetics of luminescence of Eu3+ ions in Lu2O3:Eu nanospheres with diameters of 100–270 nm and a small standard deviation of the size distribution <15% has been studied. A sharp decrease in the decay time of luminescence of Eu3+ ions in the red range with an increase in the diameter of nanospheres has been attributed to the appearance of a photon mode accelerating spontaneous luminescence, which is confirmed by the calculation of ranges of existence of whispering-gallery modes in studied nanospheres.

Specific features of the structure of ZnO nanocrystals grown in pores of Y 2 O 3 spherical matrices

A two-phase spherical Y2O3/ZnO nanocomposite particle with a diameter variable in the series of 70, 130, 180, 250, and 400 nm (variance ⩽15%) has been obtained; the first phase is a mesoporous Y2O3 matrix, while the second is a crystalline ZnO phase located in the size-limited pore volume. Specific features of ZnO nanocrystals formed on the high-curvature surface of pores with excess surface energy are studied. It is shown that the thermally activated coarsening of ZnO crystallites accompanied by an increase in the nanophase structural quality occurs during Y2O3/ZnO annealing in the temperature range t = 600–800°C. It is established that the wurtzite lattice is strained on the surfaces of small Y2O3 pores.