Spectral properties of Nd<Superscript>3+</Superscript> ions in samples of transparent Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

The spectral and luminescent characteristics of samples of Y₂O₃:Nd³⁺ ceramics obtained from different precursors under different preparation conditions (the concentration of an HfO₂ compacting additive, the temperature and time of synthesis) are studied at 300 and 77 K. It is shown that the spectral positions of absorption and luminescence lines of ceramics correspond to those of a Y₂O₃:Nd³⁺ single crystal. At the same time, the absorption and luminescence spectra show an inhomogeneous broadening, characteristic of disordered crystals and glass. The energies of the ⁴ I _9/2 and ⁴ F _3/2 Stark states of the Nd³⁺ ion are calculated. The calculation results nearly coincide with the data from the literature for the Y₂O₃:Nd³⁺ single crystal and transparent ceramics. Samples containing the compacting additive show additional lines, whose intensities correlate with its concentration and the method of preparation of Y₂O₃:Nd³⁺ ultradispersed powders. It is assumed that these lines are related to the fact that either Nd³⁺ ions enter the composition of the HfO₂ compacting additive or Hf⁴⁺ ions are present in the nearest environment of Nd³⁺ ions at the boundaries of granules enriched with HfO₂.     

Investigation of luminescence spectra of the Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> and Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce single-crystal films

The luminescence spectra of single-crystal films and bulk crystals of yttrium-aluminum garnet Y₃Al₅O₁₂ and Ce³⁺-activated Y₃Al₅O₁₂ were investigated. It was shown that the room-temperature luminescence intensity of the Ce³⁺-free single-crystal Y₃Al₅O₁₂ film was considerably lower than that of the bulk crystals, while the luminescence intensity of the Ce³⁺ ions in the Y₃Al₅O₁₂:Ce films was considerably higher than that one for the corresponding bulk crystal.     

Transport characteristics of phonons and the specific heat of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:ZrO<Subscript>2</Subscript> solid solution single crystals

The temperature dependences of the specific heat and transport characteristics of phonons in single crystals of yttrium-stabilized zirconium dioxide Y₂O₃:ZrO₂ solid solutions have been studied. It has been shown that the temperature dependences of the specific heat at T > 5 K are almost identical at the degree of stabilization of a solid solution with an Y₂O₃ content of 5–20 mol %. Differences in the temperature dependences of the specific heat of samples from different sources at T < 5 K are due to the presence of low-energy two-level systems. The features of the transport characteristics of thermal phonons at liquid helium temperatures reflect not only the presence of two-level systems but also the scattering of phonons on low-dimensional domains of another phase coherently conjugate to the main phase of the Y₂O₃:ZrO₂ solid solution.     

Diode-pumped Yb:Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>-LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> cyan laser at 501.7 nm

We describe the output performances of the 928 nm ⁴ F _3/2 → ⁴ I _9/2 transition in Nd:CLNGG under diode-laser pumping. An end-pumped Nd:CLNGG crystal yielded 1.3 W of continuous-wave output power for 17.8 W of absorbed pump power. The slope efficiency with respect to the absorbed pump power was 11.2%. Furthermore, with 17.8 W of diode pump power and the frequency-doubling crystal LiB₃O₅ (LBO), a maximum output power of 260 mW in the blue spectral range at 464 nm has been achieved. The blue output power stability over 4 h is better than 3.2%.     

Luminescence excitation in reactive molecular CO + O<Subscript>2</Subscript> collisions on the surface of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Eu

It is shown that the CO + O₂ → CO₂ catalytic reaction on the surface of Y₂O₃-Eu may lead to electronic excitation of Eu³⁺ luminescence centers due to the chemical energy release. The luminescence observed allows one to study the interaction between molecular particles of ultralow (thermal) energies with surface by optical methods.     

Sensitizer-dependent up-conversion of Ho<Superscript>3+</Superscript> in nanocrystalline Y<Subscript>2</Subscript>O<Subscript>3</Subscript>

Ho³⁺–Yb³⁺ co-doped Y₂O₃ nanocrystals were synthesized by firing hydroxy carbonate precursors. Yb³⁺-concentration-dependent up-conversion properties of Ho³⁺ in Y₂O₃ nanocrystals have been investigated. The relative intensity of up-converted red emission increases more quickly than that of the green and the near-infrared ones with the enhancement of the concentration of Yb³⁺. It is believed that the energy process ⁵ S ₂ (⁵F₄) (Ho) + ⁵ I ₇ (Ho) →⁵ I ₆ (Ho)+⁵ F ₅ (Ho) plays an important role in the population of the ⁵ F ₅ level of Ho³⁺. The result indicates that the intensity ratio of the green emission to the red one can be tuned by changing the sensitizer concentration. PACS 78.55.-m     

Femtosecond laser written stress-induced Nd:Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> (Nd:YAG) channel waveguide laser

Single tracks and pairs of tracks were written into undoped and Nd-doped YAG crystals using a commercial femtosecond laser system delivering pulses with pulse duration of 140 fs and pulse energies up to 10 μJ. The pulses were focused by a 50× microscope objective below the surface of the crystals. Due to the elasto-optical effect, stress-induced birefringence was observed in domains surrounding the single tracks and between the pairs of tracks. Waveguiding was demonstrated in certain channels in these domains. To investigate the underlying guiding mechanism highly selective chemical etching of the modified material was performed with etching rates up to 5 μm/h. Pumped at 808 nm, laser operation at a wavelength of 1064 nm was achieved. The maximum output power was 25.5 mW at 261 mW of launched pump power with a slope efficiency of 23%.     

Ground-state measurement of Pr<Superscript>3+</Superscript> in Y<Subscript>2</Subscript>O<Subscript>3</Subscript> by photoconductivity

1 at % Pr³⁺-doped Y₂O₃ single-crystal fibers were prepared using a laser-heated pedestal growth method. The emission and excitation spectra of the fibers were measured. The emissions of 4f-4f transitions from ¹ D ₂ to the ³ H ₄ and ³ H ₅ states are found at 620 and 720 nm, respectively. The ³ P ₂, ³ P ₁, ¹ I ₆, and ³ P ₀ 4f-4f absorptions are observed at 456, 472, 482, and 492 nm, respectively. A 4f-5d absorption band is detected at 288 nm. Photoconductivity measurements show that the 4f-5f transition of Pr³⁺ around 285 nm produces a direct photocurrent. Taking the onset of photocurrent to be at 320 nm, the ground state of Pr³⁺ is determined at 1.7 eV above the valence band of the host. The text was submitted by the authors in English.     

Effect of porosity and pore morphology on the low-frequency dielectric response in sintered ZrO<Subscript>2</Subscript>—8 mol% Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic compact

Effect of porosity and pore size distribution on the low-frequency dielectric response, in the range 0.01–100 kHz, in sintered ZrO₂—8 mol% Y₂O₃ ceramic compacts have been investigated. Small-angle neutron scattering (SANS) technique has been employed to obtain the pore characteristics like pore size distribution, specific surface area etc. It has been observed that the real and the imaginary parts of the complex dielectric permittivity, for the specimens, depend not only on the porosity but also on the pore size distribution and pore morphology significantly. Unlike normal Debye relaxation process, where the loss tangent vis-à-vis the imaginary part of the dielectric constant shows a pronounced peak, in the present case the same increases at lower frequency region and an anomalous non-Debye type relaxation process manifests.     

Laser-quality oxide Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> ceramics. Comparative studies of its basic characteristics and laser ceramics of a known manufacturer

The effect of sintering aids of SiO₂, ZrO₂, B₂O₃, and MgO oxides on the optimum sintering temperature, ceramics grain growth, total volume of residual pores, and optical quality of obtained ceramics is studied. The best combinations of sintering aids are found; as a result, YAG:Nd (1 at%) samples of ceramics of high optical quality are obtained. An original method for characterizing laser properties of ceramics is developed. Comparative measurements of main laser characteristics of the obtained ceramics and ceramics of the Konoshima Chemical Corp. Ltd wellknown in the world practice, are performed.     

Spontaneous luminescence of Eu<Superscript>3+</Superscript> ions in porous Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanospheres

A study of the luminescence of Eu³⁺ ions in Y₂O₃ nanospheres indicates a significant influence of the porous structure of nanoparticles on the luminescence of dopant ions. It is shown that filling the nanopores of initially porous Y₂O₃ nanospheres shortens the decay time of the spontaneous luminescence of doping europium ions. The change in the decay time is associated with the change in the effective refractive index of the porous nanospheres.     

Photolumiscent Properties of Nanorods and Nanoplates Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

Nanorods and nanoplates of Y₂O₃:Eu³⁺ powders were synthesized through the thermal decomposition of the Y(OH)₃ precursors using a microwave-hydrothermal method in a very short reaction time. These powders were analyzed by X-ray diffraction, field emission scanning electron microscopy, Fourrier transform Raman, as well as photoluminescence measurements. Based on these results, these materials presented nanoplates and nanorods morphologies. The broad emission band between 300 and 440 nm ascribed to the photoluminescence of Y₂O₃ matrix shifts as the procedure used in the microwave-hydrothermal assisted method changes in the Y₂O₃:Eu³⁺ samples. The presence of Eu³⁺ and the hydrothermal treatment time are responsible for the band shifts in Y₂O₃:Eu³⁺ powders, since in the pure Y₂O₃ matrix this behavior was not observed. Y₂O₃:Eu³⁺ powders also show the characteristic Eu³⁺ emission lines at 580, 591, 610, 651 and 695 nm, when excited at 393 nm. The most intense band at 610 nm is responsible for the Eu³⁺ red emission in these materials, and the Eu³⁺ lifetime for this transition presented a slight increase as the time used in the microwave-hydrothermal assisted method increases.     

Numerical simulation of fracture of ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic composites

The regular grid generation method was generalized for a 3D region based on the solid mechanics equations that describe deformation of a finite volume. Test calculations of fracture of ceramic composites with inclusions are represented which are based on the developed model of quasi-brittle media with regard to damage accumulation.     

Magnetodielectric coupling by exchange striction in Y<Subscript>2</Subscript>Cu<Subscript>2</Subscript>O<Subscript>5</Subscript>

We have studied the magnetodielectric response of Y₂Cu₂O₅, the so-called blue phase in the Y₂O₃-CuO-BaO phase diagram. Based on symmetry principles, we predict and demonstrate magneto-dielectric coupling on a single crystal sample. We report an anomaly in the dielectric constant at the ordering temperature of the Cu spins. We probe the magnetic field-induced phase transitions between four different magnetic phases using magneto-capacitance measurements, demonstrating relatively strong magnetodielectric coupling. We observe an increase in dielectric constant in the spin-flip phase where there exists spontaneous magnetization. We construct a detailed magnetic phase diagram. The magnetodielectric coupling is analyzed in terms of striction induced by symmetric superexchange and optical phonon frequency shifts.     

Flame-synthesized Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript> nanocrystals as spectral converting materials

In flame spray pyrolysis (FSP), the generation of uniform nanoparticles can be quite challenging due to difficulties in controlling droplet sizes during liquid spraying and uneven flame temperature. Here, we report a method to produce relatively uniform nanocrystals of a Tb³⁺ doped Y₂O₃ phosphor. In ethanol, metal nitrate precursors were simply mixed with organic surfactants to form a homogeneous solution which was then subjected to FSP. Depending on relative concentrations of the surfactant (oleic acid) to the metal precursors (yttrium and terbium nitrates), different sizes and morphologies of Y₂O₃:Tb³⁺ particles were obtained. By adjusting the surfactant concentration, Y₂O₃:Tb³⁺ crystals as small as 20~25 nm were acquired. X-ray diffraction and transmittance electron microscopy were used to prove that as-synthesized nanoparticles were highly crystalline due to the high temperature of FSP. X-ray photoelectron spectroscopy revealed that terbium dopants were well distributed throughout Y₂O₃ particles and a small portion of carbonate impurities were remained on the surface of particles, presumably originated from incomplete combustion of the organic surfactants. Photoluminescence (PL) spectra of Y₂O₃:Tb³⁺ nanocrystals exhibited a green light emission ensuring that the terbium doping was successfully occurred. However, when post-annealing was performed on the nanocrystals, their PL was dramatically enhanced indicating that quenching centers such as carbonate impurities and surface defects may have been removed by the annealing process. Owing to the continuous processability of FSP, this current method can be a practical way to produce nanoparticles in a large quantity. The obtained Y₂O₃:Tb³⁺ nanocrystals were used to fabricate a transparent film with poly-ethylene-co-vinyl acetate (poly-EVA) polymer, which was suitable for a spectral converting layer for a solar cell.

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Correction of the band gap of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Submicron samples of Y₂O₃:Eu³⁺ phosphor with elevated photoluminescence (PL) efficiency and activator concentration of 9 at % obtained by the sol–gel method were investigated by diffuse reflection spectroscopy and PL spectroscopy. It is found that the diffuse reflection spectrum in the vicinity of the fundamental absorption edge (<300 nm) is distorted by the superposition of the PL of Eu³⁺ ions, as a result of which the calculated value of optical band gap E _g of the Y₂O₃ matrix is overestimated. An algorithm for eliminating the PL influence on the absorption edge is proposed, and the correct E _g values are found to be 4.61 ± 0.12 and 4.50 ± 0.12 eV for annealing at 700 and 1300°C, respectively.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript> plasma production during pulsed laser deposition

A Nd:YAG laser operating in second harmonic (532 nm), 3 ns pulse duration, 150 mJ pulse energy, and 10 Hz repetition rate, is employed to irradiate Al₂O₃ target placed in high vacuum. The produced plasma is investigated by an ion collector used in time-of-flight configuration and by a mass quadrupole spectrometer, in order to determine the equivalent plasma temperature and the atomic and molecular composition. Pulsed laser deposition technique has been used to produce thin films on different substrates placed close to the target. Different surface analyses, such as energy dispersive X-ray fluorescence (EDXRF), X-ray photoelectron spectroscopy (XPS) and surface profilometry are employed to characterize the produced films. Measurements of ablation yield, plasma equivalent temperature, acceleration voltage and characterization of grown thin films are presented and discussed.     

Optical transmission of ceramic shielding blocks made from Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

We have studied the transmission of bulk Al₂O₃ ceramic used as heat shields for the working chamber of a turbine. We have established that radiation scattered from such an object has a pronounced speckle structure, while the scattering indicatrix is the same as the indicatrix for an ideal scatterer. We show that existing highpower semiconductor laser sources make it possible to penetrate sufficiently deeply into such materials, and the small transmission coefficient is not the limiting factor for development of optical methods for inspecting the quality of ceramic shielding blocks. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 237–240, March–April, 2007.     

Dynamics of ions produced by laser ablation of ceramic Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Al at 193 nm

We study the dynamics of ions produced upon ablation of Al and ceramic Al₂O₃ targets using nanosecond laser pulses at 193 nm (6.4 eV) as a function of the laser fluence from threshold up to 12 J cm⁻². An electrical (Langmuir) probe located at 40 mm from the target surface has been used for determining the ion yield and calculating the kinetic energy distributions. The results for both targets show the existence of a significant amount of ions having kinetic energies >200 eV (≈20% around threshold fluence), and kinetic energies are up to >1.5 keV. The results are related with the existence of direct photonionization processes caused by the photon energy of the laser being higher than the ionization potential of Al (5.98 eV). Comparison of the ion yield when ablating the two types of targets for fluences above threshold to data reported in the literature suggests that the magnitude of the yield and its threshold are parameters depending on the thermal properties of the target rather than on the laser wavelength. Around threshold, the different behavior of ion yield when ablating Al and Al₂O₃ targets suggests that the threshold for neutral aluminium and ion species in the case of ablation of the Al₂O₃ target must be similar.