Dual-wavelength competitive output in Nd:Y3Sc1.5Al3.5O12 ceramic disk laser

In this paper, we demonstrated a dual-wavelength competitive output in Nd:Y₃Sc_1.5Al_3.5O₁₂ ceramic disk laser. Different dual-wavelength output behaviors for Nd:YSAG and Nd:YAG ceramic disk laser were investigated and discussed. By applying the energy transfer model, we suggested the reasonable explanation for this new phenomenon as the disordered replacing of Al³⁺ ions by Sc³⁺ ions. The main advantage of the dual-wavelength ceramic laser is the possibility to serve as the seed source to generate Terahertz radiation.     

Determination of the electron–phonon coupling parameters from the thermal shifts of R-lines for Cr-doped garnets

The thermal shifts of R₁ and R₂ lines of Cr³⁺-doped garnets Y₃Ga₅O₁₂ (YGG), Y₃Sc₂Al₃O₁₂ (YSAG) and Gd₃Sc₂Al₃O₁₂ (GSAG) are studied by considering both the static contribution (which is frequently neglected in the previous papers) due to lattice thermal expansion and the vibrational contribution due to electron–phonon interaction. In the studies, the static contribution is calculated with the thermal expansion coefficient of the corresponding cluster in the host garnet crystals. The results indicate that the static contributions in sign are opposite to and in magnitude are about 10% of the corresponding vibrational contributions. The true electron–phonon coupling parameters α′ obtaining by taking both contributions into account increase more than 10% in comparison with the corresponding apparent electron–phonon coupling parameters α determined by considering only the vibrational contribution in the previous paper. So, to obtain the complete understanding of thermal shift of a spectral line and the true rather than apparent electron–phonon coupling parameters, one should take account of both the static and vibrational contributions.     

Solvothermal synthesis and luminescence properties of the novel aluminum garnet phosphors for WLED applications

The color rendering index (CRI) and structural stability of cerium doped yttrium aluminum garnet (YAG:Ce) based phosphors have been enhanced by replacing Y³⁺ ions by larger radius ions (Tb³⁺, Gd³⁺, Eu³⁺, and Sm³⁺) at the dodecahedral site and replacing Al³⁺ ions by larger ones (Ga³⁺, Y³⁺, Tb³⁺, Gd³⁺, and Sm³⁺) at the octahedral site. These aluminum garnet crystalline powders were prepared by solvothermal reaction method at 300 °C for 48 h. The lattice constant values of synthetic aluminum garnet crystalline powders are larger than that of YAG and the emission wavelength of Ce³⁺ ion of these samples is longer than that of YAG:Ce. FESEM and TEM studies revealed that the Ln₃Ga₂Al₃O₁₂ and Ln₃Al₂Al₃O₁₂ crystalline powders have 3-dimensional star-like morphology with submicron size and good crystallinity, while, Ln₃(LnAl)Al₃O₁₂ garnet crystalline powders were cubic crystalline phases and shaped as cubes with the round edge having an approximate diameter of about 200–400 nm. All the prepared powders were grown along (100) direction and crystallized into single crystal. Also, the effects of treatment time and reaction temperature on the structure of aluminum garnet crystalline powders have been investigated.     

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.     

Anti-ferromagnetic ordering and crystal electric field in Ce:GSAG and Ce:LLGG garnets

The magnetic susceptibility of Ce:Gd₃Sc₃Al₃O₁₂ (Ce:GSAG) and Ce:La₃Lu₂Ga₃O₁₂ (Ce:LLGG) has been studied in the temperature range from 15 to 293 K. Both the Ce-doped garnets Ce:GSAG and Ce:LLGG show anti-ferromagnetic ordering at 18 and 27 K, respectively. Crystal electric field split energy levels have been used to calculate the magnetic susceptibility following Van Vleck's model. The calculated susceptibility values reasonably agree with the experimental susceptibility data of Ce:LLGG but differ for that of Ce:GSAG system. Contribution from long-range ordering between Ce and Gd ions for anomaly in Ce:GSAG system is speculated.     

Defects in Ce-doped LuAG and YAG scintillation layers grown by liquid phase epitaxy

The single crystalline Lu₃Al₅O₁₂ (LuAG) and Y₃Al₅O₁₂ (YAG) garnet layers doped by Ce³⁺ ions were grown by the liquid phase epitaxy from the flux. The effect of the flux composition, growth conditions, and substrate polishing on the layer morphology, creation of defects, and on optical and emission properties of layers was studied. The defects typical of the epitaxial growth are discussed.     

Synthesis and characterization of mono-dispersed Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Er<Superscript>3+</Superscript>-coated SiO<Subscript>2</Subscript> nanoparticles by co-precipitation process

In this paper, a facile co-precipitation process for preparing mono-dispersed core–shell structure nanoparticles is reported. The 110 nm SiO₂ cores coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺ were synthesized and the influence of the concentration ratio of [urea]/[metal ions] on the final product was investigated. The structure and morphology of samples were characterized by the X-ray powder diffraction, Fourier transform IR spectroscopy and transmission electron microscopy, respectively. The results indicate that a layer of well-crystallized garnet Y₃Al₅O₁₂:Er³⁺ were successfully coated on the silica particles with the thickness of 20 nm. The near infrared and upconversion luminescent spectra of the SiO₂@Y₃Al₅O₁₂:Er³⁺ powders further confirm that a Y₃Al₅O₁₂:Er³⁺ coating layer has formed on the surface of silica spherical particles.     

Luminescence of La and Sc impurity centers in YAlO3 single-crystalline films

The luminescence of La_Y³⁺ and Sc_Y³⁺ and Sc_Al³⁺ centers created by lanthanum and scandium ions at Y³⁺ and Al³⁺ cation sites of YAlO₃ perovskite lattice was investigated. The features of emission of excitons localized at the mentioned centers in YAlO₃:La and YAlO₃:Sc single-crystalline films were analyzed by means of time-resolved emission spectroscopy and luminescence decay kinetics measurements under excitation by synchrotron radiation at 9 and 300 K.     

Cation distribution in Eu-Sc-Fe garnets

The cation distribution has been studied with ⁵⁷Fe Mössbauer spectroscopy in the garnet system Eu_3?ySc_2+yFe₃O₁₂ with y = 0.0, 0.2 and 0.5. It is shown that the previously proposed cation distribution is not correct. The problem of possible impurities in the investigated system is discussed in detail. Several possible cation distributions are considered compatible with Mössbauer data. Mössbauer results combined with the composition dependence of lattice constants show that the tetrahedral sites are accessible to Sc³⁺ ions. The system studied is a second example of a garnet structure in which Sc³⁺ ions are found at the tetrahedral sites. A small fraction of Sc³⁺ ions for the samples y = 0.2 and 0.5 is also found at the dodecahedral sites.     

Luminescence properties of Y3Al5O12:Ce nanoceramics

Comparative analysis of the luminescent properties of Y₃Al₅O₁₂:Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where Y_Al antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of Y_Al antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200-470 nm range related to Y_Al antisite defects and charged oxygen vacancies (F⁺ and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce³⁺ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce³⁺ ions.     

Green luminescence and EPR studies on Mn-activated yttrium aluminum garnet phosphor

Yttrium aluminum garnet (Y₃Al₅O₁₂) and Mn activated Y₃Al₅O₁₂ phosphors have been prepared by urea combustion route in less than 5 min. The phosphors are well characterized by powder X-ray diffraction, Scanning electron microscopy and Fourier-transform infrared spectroscopic techniques. Photoluminescence tests on the pure Y₃Al₅O₁₂ showed a strong green emission at 525 nm (2.36 eV) attributed to the strongly allowed transition of F⁺ center whereas in Mn²⁺ activated YAG the green emission at 519 nm is due to the ⁴T₁ (G)→⁶A₁ (S) transition of Mn²⁺ ions. EPR studies have been carried out on Mn²⁺ activated Y₃Al₅O₁₂ phosphor at 300 and 110 K. From EPR spectra the spin-Hamiltonian parameters have been evaluated. The magnitude of the hyperfine splitting (A) indicates that the Mn²⁺ ions are in a moderately ionic environment. The spin concentration (N) and paramagnetic susceptibility (χ) have been evaluated and discussed.     

Intensities of hypersensitive transitions in garnet crystals doped with Er<Superscript>3+</Superscript> ions

We examine the oscillator strengths and the intensity parameters Ω _t (t = 2, 4, 6) of yttrium-aluminum, scandium-containing, and gallium garnet crystals doped with Er³⁺ ions. A comparative analysis of the oscillator strengths and the intensity parameters Ω _t (t = 2, 4, 6) of garnets with different contents of Al³⁺ and Sc³⁺ ions (Gd_2.4Er_0.5Sc_1.8Al_3.3O₁₂, Gd_2.4Er_0.5Sc_1.9Al_3.2O₁₂, Gd_2.4Er_0.5Sc_2.0Al_3.1O₁₂) is performed, as a result of which the oscillator strengths and the intensity parameters Ω _t (t = 2, 4, 6) of these crystals are shown to have close values. We find that Ca₃(NbGa)₅O₁₂ crystals doped with Er³⁺ ions are characterized by highest values of the oscillator strengths for hypersensitive transitions and of the intensity parameter Ω₂ of Er³⁺ ions compared to the values of these quantities in the examined garnet crystals, which is determined by the fact that the symmetry of the local environment of Er³⁺ ions in these crystals is C ₁, C ₂, or C _2ν. We reveal that, as the concentration of Er³⁺ ions in these crystals increases from 1 to 39 at %, both the oscillator strength of the hypersensitive transition ⁴ I _15/2 → ² H _11/2 of Er³⁺ ions and their intensity parameter Ω₂ tend to decrease, which can be related to an increase in the relative fraction of Er³⁺ ions with higher symmetry of the local environment.     

Y3Al5O12∶Ce3+的余辉和热释光特性

高温固相法合成了Ce³⁺掺杂的Y₃Al₅O₁₂ (YAG)样品,研究了样品的结构、光致发光和热释发光性质. X射线衍射分析结果表明合成样品为YAG纯相,稀土离子的少量掺杂不改变基质YAG的结构. 荧光光谱测试表明在高温空气气氛下Y_2.95Al₅O₁₂ ∶Ce⁴⁺_0.05制备过程中存在Ce⁴⁺关键词： 长余辉 高温热释光 缺陷     

Disorder and the shape of the R-lines in Cr3+-doped garnets

This paper describes measurements of the R-line emission from Cr³⁺ ions in Y₃Ga₅O₁₂, Gd₃Sc₂Ga₃O₁₂, and Gd₃Sc₂Al₃O₁₂. Discrete splittings of the lines are interpreted as due to disorder on the cation sublattices. Assuming statistical distributions of the cations on the different cation sublattices enables estimates to be made of the degree of non-stoichiometry in the crystals.     

Effect of iso- and heterovalent additives on characteristics of highly transparent Nd(Yb):Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

The possibility of synthesis and characteristics of highly transparent Y₂O₃ ceramics doped with Nd³⁺ and Yb³⁺ were studied. The ceramics crystal structure was disordered for the first time by simultaneously substituting Y³⁺ cations by Lu³⁺ or Sc³⁺ isovalent ions and Zr⁴⁺ heterovalent ions. The developed technique allowed synthesis of highly transparent Nd³⁺:Y₂O₃, Nd³⁺: Y₂O₃ + 6 mol % ZrO₂, Nd³⁺: (Lu_0.25Y_0.75)₂O₃ + 6 mol % ZrO₂, Nd³⁺:(Sc_0.25Y_0.75)₂O₃ + 6 mol % ZrO₂, and Yb³⁺:(Sc_0.25Y_0.75)₂O₃ + 6 mol % ZrO₂ ceramics with transmittance to 82.2%. It was shown that introduction of iso- and heterovalent additives Sc₂O₃, Lu₂O₃, and ZrO₂ into Nd³⁺:Y₂O₃ decreases average crystallite sizes to ∼1 μm and reduces the pore content, thus making it possible to produce pore-free ceramics. These additives broaden the spectral band of the ⁴ F _3/2 → ⁴ I _11/2 transition of the neodymium ion to 40 nm.     

Effect of composition disorder on the electron paramagnetic resonance spectrum of the thermally populated excited state of Er<Superscript>3+</Superscript> ions in YLuAG mixed garnets

The results of investigation of electron paramagnetic resonance of Er³⁺ ions in the thermally populated first excited state in (Y_{1 − x} Lu _x )₃Al₅O₁₂ (YLuAG) mixed yttrium-lutetium garnet single crystals (0 ≤ x ≤ 1) are considered. In composition-disordered YLuAG, a number of new (as compared to Y₃Al₅O₁₂ (YAG)) Er³⁺ paramagnetic centers are detected; these centers appear due to a change in the crystal field symmetry and magnitude upon isomorphic substitution of Lu³⁺ for Y³⁺ in the yttrium sublattice of garnets. The origin of new paramagnetic centers is established and their formation probability is calculated.     

Luminescence spectroscopy of excitons and antisite defects in Lu3Al5O12 single crystals and single-crystal films

The nature of the intrinsic luminescence of the lutetium aluminum garnet Lu₃Al₅O₁₂ (LuAG) has been analyzed on the basis of time-resolved spectral kinetic investigations upon excitation of two model objects, LuAG single crystals and single-crystal films, by pulsed X-ray and synchrotron radiations. Due to the differences in the mechanisms and methods of crystallization, these objects are characterized by significantly different concentrations of Lu_Al antisite defects. The energy structure of luminescence centers in LuAG single crystals (self-trapped excitons (STEs), excitons localized near antisite defects, and Lu_Al antisite defects) has been established. For single-crystal LuAG films, grown by liquid-phase epitaxy from a Pb-containing flux, the energy parameters of the following luminescence centers have been determined: STEs in regular (unperturbed by the presence of antisite defects) sites of the garnet lattice and excitons localized near Pb²⁺ ions. The structure of the luminescence centers, related to the background emission of impurity Pb²⁺ ions, has also been established in the UV and visible ranges. It is suggested that, in contrast to the two-halide hole self-trapping, a self-trapped state similar to STEs in simple oxides (Al₂O₃, Y₂O₃) is formed in LuAG; this state is formed by self-trapped holes in the form of singly charged O^? ions and electrons localized at excited levels of Lu³⁺ cations.     

Preparation, Luminescence Properties, and Application of Scintillators Based on Lu3Al5O12:Ce Single‐Crystal Films

The possibility of obtaining scintillators with a high effective atomic number of the element Z _ef based on Lu₃Al₅O₁₂:Ce³⁺ singlecrystal films (SCF) on doping with La³⁺ and Sc³⁺ ions on Y₃Al₅O₁₂ substrates has been investigated. It is established that the SCF of (LuLaY)₃Al₅O₁₂:Ce³⁺ (Z _ef = 58.9 and = 6.67 g/cm²) does not rank below those of Y₃Al₅O₁₂:Ce³⁺ (Z _ef = 29 and = 4.52 g/cm²) in the conversion efficiency of radiation at the band with _max = 515 nm. This allows their use as screens of xray images with a space resolution of 0.75–1.00 m. It is suggested that in the SCF of Lu₃Al₅O₁₂ the isoelectronic impurities of lanthanum and scandium form radiative recombination centers of the type La_Lu, Sc_Lu, and ScAl as well as the centers Lu as a consequence of the effect of replacement of some Lu³⁺ ions by the La³⁺ ions to octanodes of the garnet lattice. The low efficiency of Ce³⁺ radiation in the SCF of (LuSc)₃(AlSc)₅O₁₂:Ce is explained by substantial losses due to excitation of the recombination luminescence in the UV region of the centers formed by the isoelectronic impurities of scandium and to the possible existence of the channel of energy excitation dissipation related to the transitions between extrema of the allowed energy bands and activator levels.     

Room temperature magnetization measurements of some substituted rare earth iron garnets

The saturation magnetization (M _s) and the initial magnetic susceptibility (χ _in) of substituted yttrium iron garnet (YIG) Ho_3−x Y _x Fe₅O₁₂ where (x=0,0.3,1.5), pure terbium iron garnet Tb₃Fe₅O₁₂, and substituted aluminum iron garnet (AlIG) Ho₃Fe_5−x Al _x O₁₂ where (x=0.05,0.7) at room temperature are reported. It has been observed that M _s and χ _in decrease in a linear manner as Ho³⁺ replaces Y³⁺ in yttrium iron garnet. For substituted (AlIG), a drastic decrease in both M _s and χ _in as Al³⁺ ions replace Fe³⁺ ions. The rate of decrease of M _s and χ _in with the increase of Al³⁺ for substituted (AlIG) is greater than that for substituted (YIG). That is attributed to the decrease in the superexchange interaction (self and mutual iron interactions) with Al substitution.     

Synthesis and Characterization of Monodispersed SiO2@Y3Al5O12:Er3+ Core-Shell Particles

Submicron core-shell structure particles SiO₂@Y₃Al₅O₁₂:Er³⁺, which silica spherical particles was coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺, were prepared by the modified Pechini-Type sol-gel method for the first time. The structure and morphology of samples were detected by the X-ray powder diffraction (XRD) measurement, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The results indicate that well-crystallized garnet nanocrystallines were formed on the surface of the silica particles. The luminescent spectra in near infrared and visible region of the core-shell structured SiO₂@Y₃Al₅O₁₂:Er³⁺ powders were also investigated and compared with those of the pure Y₃Al₅O₁₂:Er³⁺ and the Er³⁺ doped silicate glass. The results show that mono-dispersed SiO₂@Y₃Al₅O₁₂:Er³⁺ core-shell spherical particles with the near infrared, red and green luminescent emissions under the excitation of 980 nm laser diode have been successfully synthesized.