M.D. Mikhailov

Photoluminescence properties of Eu3+ ions in yttrium oxide nanoparticles: defect vs. normal sites

The position of activator ions in the lattice has a fundamental effect on the luminescent properties of phosphors. In this paper, we describe the normal and defect sites of Eu3+ ions in a Y2O3 crystal lattice, their interaction and difference in physical properties. Analytically detectable amounts of defect sites reached in Y2O3:Eu3+ nanopowders with an average size of 40–50 nm were synthesized by a novel combined Pechini-foaming method. The luminescence properties of Eu3+ ions in defect sites are most pronounced in highly doped nanocrystalline powders (32 and 40 at%). To explain this phenomenon we suggest the mechanism of irreversible energy transfer from normal to defect sites of Eu3+ ions.

Effect of synthesis conditions and surrounding medium on luminescence properties of YVO4:Eu3+ nanopowders

Abstract Nanocrystalline yttrium vanadate doped with europium ions powders were synthesized via sol-gel method based on decomposition of metal-polymer complex. X-ray diffraction analysis showed that samples had pure tetragonal phase without any impurities. Scanning electron microscopy and static light scattering technique were used to study morphology and size of prepared nanoparticles. Average diameter of the nanoparticles was about 40 nm. The changes in structural and luminescence properties were observed as a function of the first and second calcination temperature. The optimal conditions for synthesis of nanoparticles were determined as T 1 =500 °C, t 1 =1 h; T 2 =950 °C, t 2 =1.5 h. The effect of different media surrounding the nanoparticles on their luminescence properties and lifetime was investigated and discussed in terms of effective refractive index. It was found that the observed lifetime of YVO 4 :Eu 3+ 5 at.% nanophosphor was decreased from 0.64 ms in air ( n med =1) to 0.45 ms in chalcogenide glass As 39 S 61 ( n med =2.39).

Synthesis and study of Y2O3:Eu3+ nanoparticles

The synthesis method of weakly agglomerated Y2O3 powders based on the decomposition of metal–polymer gel (Pechini method) has been developed. The physicochemical properties of powders synthesized by the standard Pechini method and a method using foaming components have been compared. The luminescence properties of Eu3+-doped Y2O3 have also been studied.

Photoinduced bleaching in Ga-Ge-S(Se) vitreous films

Vitreous films in the Ga-Ge-S(Se) system are prepared through pulsed laser deposition and investigated. An analysis of the data of Raman and energy-dispersive X-ray spectroscopy demonstrates that the composition and structure of the films are similar to those of the monolithic glass. Exposure of the films to radiation with an energy higher than the band gap leads to bleaching of sulfur-based films due to the local oxidation of the films as judged from the data of infrared, Raman, and energy-dispersive X-ray spectroscopy. The replacement of sulfur by selenium in the composition of the films results in the opposite effect: irradiation of the films brings about the photoinduced darkening. Examination of the samples with the use of a scanning electron microscope does not reveal a substantial change in the morphology of the films under irradiation. The observed effect is used to write a copy of the diffraction grating with a resolution of 1200 grooves/mm.

YVO 4 :Nd 3+ nanophosphors as NIR-to-NIR thermal sensors in wide temperature range

We report on the potential application of NIR–to–NIR Nd3+-doped yttrium vanadate nanoparticles with both emission and excitation operating within biological windows as thermal sensors in 123–873 K temperature range. It was demonstrated that thermal sensing could be based on three temperature dependent luminescence parameters: the luminescence intensity ratio, the spectral line position and the line bandwidth. Advantages and limitations of each sensing parameter as well as thermal sensitivity and thermal uncertainty were calculated and discussed. The influence of Nd3+ doping concentration on the sensitivity of luminescent thermometers was also studied.

Lead-containing oxyhalide glass

New glass compositions in the PbO-PbCl2-PbBr2 system are synthesized and the region of vitrification is established. The temperature of sample vitrification is determined using the technique of differential-thermal analysis and the influence of the components on the temperature of vitrification has been studied. Infrared, Raman, and X-ray photoelectronic spectra are registered, suggestions about the glass structure are made, and the X-ray-phase analysis has been carried out. The density is measured and the refractive index of glass is estimated.

Photosensitivity of As-S-based chalcogenide photoresists in the recording of relief phase holograms

The photosensitivity of AsxSb(Ge)yS100-x-y (x equals 35 - 45, y equals 0 - 6) films to light with wavelength 488 nm was investigated. The value of photosensitivity was quantified using the results of chemical etching in amine solutions for as-deposited and exposed films. It was found the exposure required to obtain the optimal relief depth, which is from 0.1 to 0.3 micrometer for holographic gratings, decreases with both sulfur and antimony content from about 2 J/cm2 for As2S3 to about 0.3 J/cm2 for As30Sb4S66. The photosensitivity of the Ge doped films is sharp decreased with Ge content. A model of effect of additives on the change of dissolution kinetics was proposed. It is based on the consideration of a photopolymerization of films leading to the formation of the insoluble network of AsS3/2 structural units.

Photostructural transformation of chalcogenide glasses under nonlinear absorption of laser radiation

The photoinduced change of transmittancy of chalcogenide glasses was investigated under exposure to the laser radiation at 1.064 and 1.318 micrometer. It was established that two- photon absorption in these glasses arises under exposure to radiation with irradiances of greater than or equal to 108 W/cm2. It results in irreversible structural transformation of the glasses in the interaction region. This process has threshold character over a narrow range of radiation irradiance (plus or minus 0.1Ithr) and results in appearance of a small-dispersion phase in the bulk glass. Formation of such regions has fluctuating character and causes the appearance of strong light scattering. The effect observed is similar phenomenologically to the known effect of photo-structural transformations in the thin films under exposure to near bandgap light. However, in contrast to the last, the emerged changes of the glass properties are not erased completely by the annealing at the glass transition temperature.

Pulsed laser and photosensitive chalcogenide layers application to relief holographic structure manufacturing

The pulsed Nd-laser application to holographic relief manufacturing on the ion-beam sputtered chalcogenide layers is described. The masks formed by this way permit us to transfer the relief into glass and copper wafers.