Timing characteristics of the scintillation response of Gd3Al2Ga3O12:Ce and Gd3Al2.6Ga2.4O12:Ce single crystal scintillators

The timing characteristics of scintillation response of Czochralski-grown Gd₃Al₂Ga₃O₁₂:Ce and Gd₃Al_2.6Ga_2.4O₁₂:Ce single crystals were compared. The photoelectron yield, scintillation decay times, and coincidence time resolution were measured. At 662 keV γ-rays, the photoelectron yield of 6200 phe MeV⁻¹ obtained for Gd₃Al₂Ga₃O₁₂:Ce is higher than that of 4970 phe MeV⁻¹ obtained for Gd₃Al_2.6Ga_2.4O₁₂:Ce, while an inferior energy resolution of the former (7.2% vs. 5.6%) is observed. Scintillation decays are approximated by sum of exponentials with the dominant fast component decay time and its relative intensity of 89 ns (73%) for Gd₃Al₂Ga₃O₁₂:Ce and 136 ns (69%) for Gd₃Al_2.6Ga_2.4O₁₂:Ce. The coincidence time resolution obtained for Gd₃Al₂Ga₃O₁₂:Ce is superior than that of Gd₃Al_2.6Ga_2.4O₁₂:Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay characteristics of the light pulse.     

Epitaxial films (Bi,Gd)3(Ga,Pt)2Ga3O12 grown by liquid-phase epitaxy

Single-crystal films of complex composition (Bi,Gd)₃(Ga,Pt)₂Ga₃O₁₂ on Gd₃Ga₅O₁₂(111) substrates are synthesized by liquid-phase epitaxy from a supercooled solution-melt based on Bi₂O₃-B₂O₃ flux. Optical absorption of Bi³⁺ and Pt³⁺ ions in these films is investigated in the wavelength range from 200 to 860 nm.     

Optical absorption by Nd<Superscript>3+</Superscript> and Gd<Superscript>3+</Superscript> ions in epitaxial films grown on Gd<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> substrates from a lead-containing solution melt

Epitaxial films of composition (Gd,Nd)₃Ga₅O₁₂ or (Gd,Y,Nd)₃Ga₅O₁₂ with a neodymium content varying from 0.3 to 15 at. % are grown by liquid-phase epitaxy from a supercooled PbO-B₂O₃-based solution melt on Gd₃Ga₅O₁₂(111) substrates. The optical absorption spectra of the epitaxial films grown are measured in the wavelength range 0.2–1.0 µm. The results of interpreting the absorption bands observed in the spectra are used to construct the energy level diagrams of Nd³⁺ and Gd³⁺ ions in the matrices of the epitaxial films.     

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.     

Phase-matched second-harmonic generation at 440 nm in a LiNbO3 -Gd3Ga5O12 waveguide with a tunable stimulated Raman source

Using a tunable stimulated Raman source, we have observed second-harmonic generation in the blue in a sputtered LiNbO₃ film deposited on Gd₃Ga₅O₁₂. With the choice of Gd₃Ga₅O₁₂ as a substrate, it becomes possible to both phase-match a large range of fundamental wavelengths as well as have an excellent epitaxial quality surface. The SHG efficiency for the TM^ω₀ → TM^2ω₂ phase matched conversion process is estimated to be ～ 10^-4.     

Ferromagnetic resonance in epitaxial (Bi,Lu)3(Fe,Ga)5O12(210) films

Ferromagnetic resonance in epitaxial (Bi,Lu)₃(Fe,Ga)₅O₁₂ films grown on Gd₃Ga₅O₁₂(210) substrates is investigated. The spectrum contains a number of peaks, the most intense of which is related to the bulk of the film and the transition layer at the film-substrate interface. Most of the film volume is characterized by reduced magnetic anisotropy. The azimuthal and polar dependences of the resonance field exhibit 180° symmetry.     

Multisites Cr3+ in GGG and GSGG garnets

The emission and excitation spectra of Cr³⁺ -doped Gd₃Ga₅O₁₂ (GGG) and Gd₃Sc₂Ga₃O₁₂ (GSGG) are explained in the light of multisite effects. The situation is particularly complicated in the case of GSGG, where the different sites have²E energy levels near each other which overlap with the⁴A₂ →⁴T₂ absorption bands. The spectra obtained under selective excitations are interpreted on the multisite assumption.     

Gd3Ga5-xAlxO12单晶低温磁性的实验研究

采用提拉法制备了Gd₃Ga_5-xAl_xO₁₂(以下简称GGAG)单晶,经X射线粉末照相证实为石榴石型单相结构。在T=1.5—77K温区里,场强从45—60000Oe范围内,沿[111]晶轴方向测量了磁化强度和磁化率,并与本文所用钇镓石榴石Gd₃Ga₅O₁₂(以下简称GGG)和文献[1,2]报道的GGG单晶数据作了比较。实验结果表明:(1)在场强H<500Oe时,磁化率X与温度T的关系遵守居里-外斯定律,其有序温度T_N远低于1.5K;(2)H>10000Oe时,该材料的磁化强度(或磁化率)比GGG高3—4％;(3)在H～30000Oe时,特定温度T_min对应的临界场H_c比GGG约高4000Oe。实验研究表明,采用离子代换法寻找新的性能良好的磁致冷剂的途径是可行的。 关键词：     

Gd3Ga5O12:Ag薄膜电致发光材料的制备及其发光性质

研究了Gd₃Ga₅O₁₂:Ag材料的制备及其发光性质.Gd₃Ga₅O₁₂:Ag材料通过固相反应法制得,采用X射线衍射法分 析了材料的结晶度及成分.用电子束蒸发将该材料制备成交流的薄膜电致发光器件,得到了 较好的蓝紫色发光,发光峰分别位于397和467nm.通过对材料的光致发光和激发光谱的研究 和比较,得出397和467nm分别来自于氧空位和Ag⁺的发光.     

Multisites Cr3+ in GGG and GSGG garnets

The emission and excitation spectra of Cr³⁺ -doped Gd₃Ga₅O₁₂ (GGG) and Gd₃Sc₂Ga₃O₁₂ (GSGG) are explained in the light of multisite effects. The situation is particularly complicated in the case of GSGG, where the different sites have²E energy levels near each other which overlap with the⁴A₂ ⁴T₂ absorption bands. The spectra obtained under selective excitations are interpreted on the multisite assumption.     

Photoinduced features of Y3Fe5 O12 nanocrystalline films

We have studied the photoinduced effects in the nanocrystallized Y₃Fe₅O₁₂ films deposited on the Gd₃Ga₅O₁₂ <1 1 1> substrates. We have found for the first time substantial changes of the birefringence, two-photon absorption and circularly polarized absorption in different regimes of treatment of the nanocrystallized films. The explanations of the observed phenomena are suggested. The absorption spectra were modeled by the DFT based calculations of the electronic structure and density of states, which have revealed the well-pronounced differences between the densities of states of the tetra- and octahedrally coordinated iron ions. In addition, the crystal field calculations of the Fe³⁺ energy levels at the octahedral and tetrahedral positions have been performed.     

Infrared spectroscopy and lattice dynamical calculations of Gd3Al5O12, Tb3Al5O12 and Lu3Al5O12 single crystals

The infrared (IR) reflectance spectra of Gd₃Al₅O₁₂, Tb₃Al₅O₁₂ and Lu₃Al₅O₁₂ single crystals are studied for the first time. At room temperature, 15 infrared active modes for Lu₃Al₅O₁₂ and 14 for Gd₃Al₅O₁₂, Tb₃Al₅O₁₂, out of the 17 theoretically predicted, have been experimentally recorded. The complex dielectric function the refractive index, the absorption coefficient as well as the longitudinal (ω_LO) and transverse (ω_TO) frequencies of the long-wavelength T_1u modes are determined by the Kramers-Kronig transformation of the reflectance spectra. The experimental data are compared and discussed with the theoretical results obtained by the rigid ion model. Our theoretical analysis reveals that the bonds in the tetrahedra exhibit a covalent character while those in the dodecahedra almost ionic character, which is in accordance with the results for other materials of this crystal family.     

Morin transition in annealed iron implanted garnets

Y₃Fe₅O₁₂, Y₃Al₅O₁₂ and Gd₃Ga₅O₁₂ single crystal granets were implanted with 10¹⁷iron.cm⁻². Complementary techniques: CEMS, TEM and XRD at glancing angles have allowed to follow the behavior of implanted iron during thermal annealings. For Y₃Fe₅O₁₂ large α-Fe₂O₃ particles are formed after annealings and at 1200°C occurs a low temperature regime of the Morin transition at room temperature. For Y₃Al₅O₁₂, due to aluminium substitution in the precipitates, the Morin transition is only detected after an annealing at 1300°C whereas in Gd₃Ga₅O₁₂ no Morin transition is observed.     

Thermal decay of stable colour centres in Gd3Ga5O12 crystals

This work is devoted to an analysis of thermal decay processes of the stable colour centres (CC) created in gadolinium gallium garnet (GGG) Gd₃Ga₅O₁₂, crystals under irradiation by gamma-quanta (E=1.25 MeV, D=10⁶ Gy). An analysis of the model of CC accumulation under irradiation as well as an isochronous heating model is presented. The decay activation energy (Δ E) for O^? and F centres in GGG crystals is calculated in accordance with this model.     

Improvement of the scintillation properties of Gd3Ga3Al2O12:Ce,B single crystals having tailored defect structure

A novel approach is reported to minimize various defect centers in Ce doped Gd₃Ga₃Al₂O₁₂ single crystals to improve the scintillation properties. The crystals of Gd₃Ga₃Al₂O₁₂ codoped with 0.2 at% Ce and B (GGAG:Ce,B) have been grown in air and argon ambient using the Czochralski technique. The scintillation light output of crystals grown in Ar ambient was significantly increased after annealing the crystals in air. The measured light output of 60000 ph/MeV for annealed crystals is the highest value reported among this class of materials. As a consequence, the energy resolution at 662 keV gamma‐rays from a ¹³⁷Cs source was improved from 8% for the crystals grown in air to 6% for crystals grown in Ar and subsequently annealed in air. Further, the thermal quenching energy of photoluminescence (PL) emission was increased to be 470 meV for the annealed crystals. The thermoluminescence (TL) measurements suggest that the crystals grown in Ar ambient and post‐growth annealed in air may have a lesser concentration of trap centers which subsequently lead to the improvement in optical and scintillation properties leading to a superior detector performance. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Deep trapping states in cerium doped (Lu,Y,Gd)3(Ga,Al)5O12 single crystal scintillators

We study deep trapping states in Ce³⁺-doped garnet crystals with the composition (Lu,Y,Gd)₃(Ga,Al)₅O₁₂, recently shown as having remarkably high light yield. We use thermally stimulated luminescence (TSL) technique above room temperature and determine the composition Gd₃Ga₃Al₂O₁₂ as the host showing the lowest concentration of traps. This host consistently manifests very low afterglow comparable to that of the standard BGO crystal. We also perform TSL glow peak analysis based on the initial rise technique to evaluate trap depth and other characteristics associated with TSL peaks.     

Ferromagnetic resonance in (Bi,Tm)<Subscript>3</Subscript>(Fe,Ga)<Subscript>5</Subscript>O<Subscript>12</Subscript>(210) epitaxial films

It is shown that the ferromagnetic resonance spectrum in (Bi,Tm)₃(Fe,Ga)₅O₁₂ films grown in Gd₃Ga₅O₁₂(210) substrates has a single peak. The azimuthal and polar dependences of the resonance field possess 180° symmetry. The angular dependences of the ferromagnetic resonance line width and intensity are studied.     

Phosphorescence of a gadolinium gallium garnet single crystal

The phosphorescence of a Gd₃Ga₅O₁₂ single crystal grown by the Czochralski method is discussed. The phosphorescence was excited by UV radiation of a deuterium lamp.     

Synthesis and luminescence properties of Er3+-doped Lu3Ga5O12 nanocrystals

The concentration-dependent luminescence properties of sol–gel-derived nanocrystalline Lu_3(1?x)Er_3xGa₅O₁₂ powders (where x=0.01, 0.05 and 0.1) have been studied. Laser-excited luminescence spectra, emission decays and upconversion luminescence of Er³⁺-doped Lu₃Ga₅O₁₂ nanocrystalline samples have been measured. The decay curve of the (²H_11/2,⁴S_3/2) emission exhibits a non-exponential behavior presumably due to cross-relaxation process. Moreover, near-infrared to visible upconversion luminescence has been observed in the green region for 1.0 mol% Er³⁺ ions in Lu₃Ga₅O₁₂ nanocrystals upon 815 nm excitation. The power dependence of the anti-Stokes luminescence suggests that upconversion is probably achieved through the sequential absorption of two photons. To the best of our knowledge, this is the first report on the preparation and optical properties of Er³⁺-doped Lu₃Ga₅O₁₂ in the form of nanocrystalline powders.