D. Hreniak

Synthesis and optical properties of Nd3+-doped Y3Al5O12 nanoceramics

The Nd-doped yttrium aluminum garnet (Nd:YAG) nanocrystallites were prepared by the sol–gel method. The preparation technology for semi-transparent ceramics is described. Their structure and morphology were studied by XRD. The emission properties of Nd:YAG measured for nanopowders and ceramics are reported. In particular the spectra were measured as a function of excitation power. It was found that with increasing excitation power, there was increased emission from the 4F5/2 state. The effect of grain size on luminescence properties was observed.

White emission of lithium ytterbium tetraphosphate nanocrystals.

An efficient anti-Stokes white broadband emission induced by 976 nm laser diode in lithium ytterbium tetraphosphate (LiYbP4O12) nanocrystals was investigated. The emission occurs at room temperature and atmospheric pressure. Its intensity demonstrates an evident threshold dependence on the temperature and excitation density characteristic to avalanche process. The white emission is accompanied by very efficient photoconductivity characterized by microampere photocurrent which increases with the fourth order of applied incident light power (~P4). We show that this emission is critically dependent on temperature and increases significantly in vacuum. It is concluded that the anti-Stokes white emission is associated with theYb3+- CT luminescence.

Rare-earth doped nanocrystalline phosphors for field emission displays

The cathodoluminescence properties of rare-earth (RE = Ce, Eu, Tb) doped nanocrystalline phosphors (Y2O3, Y3Al5O12) were investigated. Their structure and morphology were determined and correlated with optical properties. The effect of grain sizes on emission yield of RE doped nanophosphors has been investigated. A possibility of application of RE doped nanophosphors for efficient field emission display (FED) devices has been discussed.

Preparation and optical properties of nanocrystalline and nanoporous Tb doped alumina and zinc aluminate

Abstract Preparation and morphology of nanocrystalline and nanoporous ceramics composed of a network of alumina and zinc aluminate doped with Tb ions are reported. The pore size distributions are determined by nitrogen adsorption at 77 K. The emission spectra and lifetimes of Tb 3+ ions were measured. The effect of thermal conditions of preparation on emission properties was investigated. It is concluded that with increasing thermal heating the sizes of nanoparticles increase leading to the cluster formation of Tb 3+ ions.

Optical behavior of Eu3+-doped BaTiO3 nano-crystallites prepared by sol–gel method

Abstract Eu 3+ -doped BaTiO 3 nano-crystallites with grain sizes 32–38 nm have been obtained by a sol–gel method. It has been found that the luminescence characteristics are strongly dependent on the sintering temperature. Powders sintered at temperatures below 1000 °C demonstrate a luminescence behavior at room temperature associated with a lack of the inversion symmetry of Eu 3+ sites. Above 1000 °C nano-crystallites undergo a phase transition characterized by an inversion symmetry of Eu 3+ sites. The size effect of Eu 3+ :BaTiO 3 nano-crystallites on luminescence characteristics is observed.

Properties of Tb-doped vacuum-sintered Lu2O3 storage phosphor

Tb3+-doped Lu2O3 sintered ceramics were prepared in vacuum and in air. It was shown that the vacuum-sintered disks are able to store energy when irradiated with 300-nm or shorter photons. A small part of the stored energy could be recovered with 980-nm light. A much more significant amount of the stored energy could be released with red 647-nm photons. However, recovering the total stored energy could be accomplished only upon heating up to about 300 °C. Changes in absorption of the raw materials upon ultraviolet irradiation and subsequent IR (980 and 647 nm) treatments or upon heating at 300 °C are presented and discussed. A model for energy storing and recovering through the various IR irradiations or through heating is presented. At least two distinct ways of hole trapping as Tb4+ or Vk-center as well as creation of F and F+ is suggested.

Anti-Stokes bright yellowish emission of NdAlO3 nanocrystals

Infrared laser diode–induced anti-Stokes bright yellowish emission of NdAlO3 nanocrystalline powder was observed at room temperature in ambient atmosphere. The emission intensity was found to be unaltered with lowering temperature and to increase by two orders of magnitude in vacuum. The temperature of bright emission under ambient atmosphere was determined to be 350 °C. It was found that the yellowish emission was accompanied by a giant photocurrent of 0.5 microamperes at relatively low applied voltage. The power dependence of the photocurrent was governed by an avalanche-like mechanism. The origin of the bright emission is discussed in terms of charge transfer luminescence of Nd3+.

Controlling luminescence colour through concentration of Dy3+ ions in LiLa1−xDyxP4O12 nanocrystals

Luminescence and excitation spectra of LiLa1−xDyxP4O12 nanocrystals are reported. In particular, the impact of dopant concentration on the luminescence properties of LiLa1−xDyxP4O12 nanocrystals was investigated. It was found that increase in Dy3+ concentration results in a strong quenching of luminescence. The mechanism of concentration quenching was discussed in terms of the Yokota–Tanimoto model. It is concluded that with increasing Dy3+ concentration, the donor–acceptor interaction leads to a significant concentration quenching resulting in nonexponential luminescence decay, whereas at a high concentration limit the donor–donor interaction becomes dominant and exponential decay is observed.

Structural and spectroscopic characterization of Lu2O3:Eu nanocrystalline spherical particles

Spherical particles of Lu2O3:x% Eu, with x varying from 0% to 10% with respect to Lu, were prepared by precipitating hydroxides with urea at 80 °C and subsequently decomposing these hydroxides to oxides at 650 °C. TEM pictures revealed that the spherical particles were very uniform in size and their diameters were about 130 nm. Each of the particles consisted of crystallites about 20 nm in diameter. Luminescence and excitation spectra contained all the characteristic features of the Eu3+ ion. The most intense line in the emission was located around 611 nm. Energy transfer was observed from the Eu3+ ions occupying the S6(C3i) centrosymmetric site to the Eu3+ located in the non-centrosymmetric position of C2 symmetry. The decay kinetics were slightly non-exponential, especially for the lowest dopant concentrations. At liquid nitrogen temperature the average decay time for the 0.2% powder was shorter by about 40% compared to the 3–10% materials. At room temperature the average decay time varies only slightly. Rise times were observed for all concentrations at room temperature but only for higher concentrations at liquid nitrogen temperature. This effect is in contrast to that of nanoparticles of Lu2O3:Eu prepared using different synthesis procedures.

Nature and optical behaviour of heavily europium-doped silica glasses obtained by the sol–gel method

Abstract Silica glasses doped with Eu 3+ were prepared by the sol–gel method. The effects of the synthetic procedure on optical properties of the europium heavily doped glasses have been investigated. The fluorescence characteristics of Eu 3+ have been measured for several thermal stages of the sol–gel process. In particular, we have studied aggregation of the Eu ions leading to creation of nanocrystallites during the thermal treatment of silica glasses. The size of the nanocrystalites and their structure have been determined by means of high-resolution transmission electron microscopy and X-ray diffraction. The influence of the OH − groups on the luminescence lifetimes of Eu 3+ has been studied. A broad luminescence band in the blue region has been observed for the silica glasses possessing silanol (Si–OH) groups. Its intensity decreases with the increasing temperature of sintering for the samples treated in the presence of NH 4 Cl. In the case of those heated at high temperatures, doubly doped with Eu and Al silica glasses, a blue emission assigned to the Eu 2+ ions has been observed. Its intensity increases with the Al 3+ ions concentration.