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 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.     

Absorption spectra of Bi3+ and Fe3+ in Y3Ga5O12

The absorption spectra of Y₃Ga₅O₁₂:(Fe³⁺), Y₃Ga₅O₁₂:(Bi³⁺) and Y₃Ga₅O₁₂:(Bi³⁺, Fe³⁺) are presented to 40,000 cm^-1. Assignments are discussed and the transitions analysed in terms of their involvement in the large Faraday rotation observed in bismuth substituted iron garnets.     

EPR study of the impurity paramagnetic centres in (CaO−Ga2O3−GeO2) glasses

The X-band EPR spectra of Cr³⁺, Mn²⁺, and Fe³⁺ impurity ions in glasses of (CaO?Ga₂O₃?GeO₂) system are investigated in the 77÷300 K temperature range. The experimental data analysis yields the following results: (i) Impurity chromium ions are incorporated into the (CaO?Ga₂O₃?GeO₂) glasses network in Cr³⁺ (3d³,⁴F_3/2) paramagnetic valence state only and occupy the strong distorted oxygen coordinated octahedral sites. (ii) For all activated and non-activated (CaO?Ga₂O₃?GeO₂) glasses the iron impurity is present at concentration roughly 0.01 wt.%. Isotropic EPR signals atg _eff=4.29 andg _eff=2.00 are assigned to Fe³⁺ (3d⁵,⁶S_5/2) ions in the sites with strong rhombic distortion and in the sites with nearly cubic symmetry respectively. (iii) The manganese EPR spectrum in (CaO?Ga₂O₃?GeO₂) glasses is weakly dependent on temperature, doping procedure as well as manganese concentration. EPR spectra of impurity manganese ions in glasses with Ca₃Ga₂Ge₃O₁₂ and Ca₃Ga₂Ge₄O₁₄ compositions are virtually identical and belong to Mn²⁺ (3d⁵,⁶S_5/2) ions. Impurity manganese ions are incorporated into the (CaO?Ga₂O₃?GeO₂) glass network as isolated Mn²⁺ centres and clusters of Mn²⁺ ions.     

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.     

La掺杂对Bi4Ti3O12薄膜铁电性能的影响

利用Sol-Gel法在Pt/Ti/SiO₂/Si衬底上制备出Bi₄Ti₃O₁₂和Bi_3.25La_0.75Ti₃O₁₂薄膜，研究了La掺杂对Bi₄Ti₃O₁₂薄膜的晶体结构、铁电性能和疲劳特性的影响，发现La掺杂没有改变Bi₄Ti₃O₁₂薄膜的基本晶体结构，并且提高了Bi₄Ti₃O₁₂铁电薄膜的剩余极化值和抗疲劳性能，对La掺杂改善Bi₄Ti₃O₁₂铁电薄膜性能的机理进行了讨论. 关键词： 铁电性能 4Ti₃O₁₂薄膜')" href="#">Bi₄Ti₃O₁₂薄膜 3.25La_0.75Ti₃O₁₂薄膜')" href="#">Bi_3.25La_0.75Ti₃O₁₂薄膜 sol-gel法 La掺杂     

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.     

A simple photochemical method to synthesize Ga2O3-Dy-M thin films and their evaluation as optical materials (where M=Cr or Co)

We report the photochemical method to synthesize Ga₂O₃-Dy³⁺-Co³⁺ and Ga₂O₃-Dy³⁺-Cr³⁺ thin films. X-ray photoelectron spectroscopy, X-ray diffraction and photoluminescence were used to characterize the products. These analyses revealed that as-deposited and annealed films are amorphous. The optical characterization of the films showed that these are highly transparent in the visible spectrum but decrease significantly with doped and co-doped films. Under the excitation of UV light (254 nm) the doped films (Ga₂O₃-Dy³⁺) show the characteristic emissions of Dy³⁺ at 500, 575, 594, 605 and 652 nm corresponding to ⁴F_9/2→⁶H_J ( J=15/2, 13/2 and 11/2) transitions but the emissions decrease with the co-doped films (Ga₂O₃-Dy³⁺-M³⁺, where M=Cr or Co); a possible emission mechanism and energy transfer have been proposed.     

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.     

Chemical,optical, and electrical characterization of Ga2O3 thin films grown by plasma-enhanced atomic layer deposition

Thin Ga₂O₃ films were grown on Si (100) using trimethylgallium (TMG) and oxygen as the precursors through plasma-enhanced atomic layer deposition. The depositions were made over a temperature range of 80–250?°C with a growth per cycle of around 0.07 nm/cycle. Surface self-saturating growth was obtained with TMG pulse time ≥20?ms?at a temperature of 150?°C. The root mean square surface roughness of the obtained Ga₂O₃ films increased from 0.1?nm to 0.3?nm with increasing the growth temperature. Moreover, the x-ray photoelectron spectroscopy analysis indicated that the obtained film was Ga-rich with the chemical oxidation states Ga³⁺ and Ga¹⁺, and no carbon contamination was detected in the films after Ar⁺ sputtering. The electron density of films measured by x-ray reflectivity varied with the growth temperature, increasing from 4.72 to 5.80?g/cm³. The transmittance of Ga₂O₃ film deposited on a quartz substrate was obtained through ultraviolet visible (UV–Vis) spectroscopy. An obvious absorption in the deep UV region was demonstrated with a wide band gap of 4.6–4.8?eV. The spectroscopic ellipsometry analysis indicated that the average refractive index of the Ga₂O₃ film was 1.91?at 632.8?nm and increased with the growth temperature due to the dense structure of the films. Finally, the I-V and C-V characteristics proved that the Ga₂O₃ films prepared in this work had a low leakage current of 7.2?×?10^?11 A/cm² at 1.0?MV/cm and a high permittivity of 11.9, suitable to be gate dielectric.     

Temperature‐dependent Raman scattering in ferroelectric Bi4−xNdxTi3O12(x = 0, 0.5, 0.85) single crystals

The temperature‐dependent Raman spectra of ferroelectric Bi_4−xNd_xTi₃O₁₂(x = 0, 0.5, 0.85) single crystals were recorded from 100 to 800 K. It was found that there is a critical Nd content x₀ between 0.5 and 0.85. The Nd³⁺ ions prefer to replace Bi³⁺ ions in pseudo‐perovskite layers when x < x₀, while they might begin to incorporate into (Bi₂O₂)²⁺ layers when x ≥ x₀. Nd substitution leads to a decrease in the ferroelectric–paraelectric transition temperature (T_c). A monoclinic distortion of orthorhombic structure occurs in Bi₄Ti₃O₁₂ crystals at temperatures below 200 K. Copyright © 2009 John Wiley & Sons, Ltd.     

Calculations of the optical and EPR spectral data for Cr3+ ion in Y3Ga5O12 crystal from the complete diagonalisation method

The complete diagonalisation (of energy matrix) method is applied in this paper to calculate together the optical and electron paramagnetic resonance (EPR) spectral data for Cr³⁺ ion at the trigonal Ga³⁺ site of Y₃Ga₅O₁₂ crystal. The method is founded on the two-spin-orbit-parameter model where in addition to the contributions from the spin-orbit parameter of central dⁿ ion (i.e., one-spin-orbit-parameter model) in the traditional crystal field theory, those from the spin-orbit parameter of ligand ion via covalence effect is also considered. The calculated results propose that by using only four adjustable parameters, the 12 observed spectral data (nine optical band positions and three EPR parameters g_//, g_⊥ and D) in Y₃Ga₅O₁₂: Cr³⁺ are reasonably explained. The impurity-induced local lattice distortion of Cr³⁺ in Y₃Ga₅O₁₂ crystal is also estimated through the calculations. The results are discussed.     

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.     

Liquid-phase epitaxy and optical absorption of gadolinium-gallium garnet films grown from a PbO-B2O3 solution melt on Gd3Ga5O12 substrates

The optical absorption due to impurity ions was studied in gadolinium-gallium garnet single crystal films with a stoichiometric composition Gd₃Ga₅O₁₂ grown by liquid-phase epitaxy from a supercooled PbO-B₂O₃ solution melt on (111)-oriented Gd₃Ga₅O₁₂ substrates.     

Absorption spectra and magneto-optic figures of merit in the Bi x Sm3-x Fe5-y Ga y O12 system

The absorption (α) and Faraday rotation (θ) spectra of 14 garnets belonging to the series Bi _x Sm_3-x Fe_5-y Ga _y O₁₂ (0<x<1.05, 0.8<y<1.15) have been measured between 15 000 cm⁻¹ and 19 000 cm⁻¹. The figure of merit (θ/α) at 17 850 cm⁻¹ (560 nm) increases linearly with increasing bismuth concentration up tox∼0.6 where it begins to increase less rapidly. For operation of magneto-optic display devices at 17 850 cm⁻¹ there is no advantage in using garnets in this series withx>0.8. The Faraday rotation at 17 850 cm⁻¹ increases linearly with bismuth concentration whereas the absorption coefficient increases more rapidly. The presence of Bi³⁺ increases the intensity of all Fe³⁺ pair transitions in the garnet system as a result of the increased superexchange induced by Bi³⁺. This is in keeping with the observation that the intensity of the⁶A_1g (S)→⁴T_1g (G) transition in (RE)₃Fe₅O₁₂ (RE=Er, Y, Dy, Gd, Eu) increases on traversing the above RE series as do the Curie temperatures of these iron garnets.     

Influence of mobile space charges on electrical properties of ferroelectric Bi3.5La0.5Ti3O12 thin films

Lanthanum-substituted bismuth titanate, Bi_3.5La_0.5Ti₃O₁₂ (i.e., x=0.5 in Bi_4−xLa_xTi₃O₁₂), thin films have been grown on Pt/Ti/SiO₂/Si substrates using pulsed laser deposition. The frequency dependence of the real part ε′(ω) and the imaginary part ε″(ω) of the dielectric constant has been studied. The ε′(ω) does not show any sudden change within the frequency range of 10²-10⁶ Hz. In contrast, the ε″(ω) shows a large dispersion as frequency decreases. The observed relaxation behavior in ε″(ω) can be explained in terms of a migration of oxygen vacancies in (Bi₂O₂)²⁺ layers, not in Bi₂Ti₃O₁₀ perovskite layers.     

Ga2O3组分对Tm3+掺杂GeO2-Ga2O3-Li2O-BaO-La2O3玻璃的光谱性能影响

制备了Tm³⁺(8.0mol%)掺杂(77-x)GeO₂-xGa₂O₃-8Li₂O-10BaO-5La₂O₃(x=4,8,12,16)系列玻璃.系统地研究了Ga₂O₃从4mol%变化到16mol%时,玻璃的光谱性质与热学性质的变化规律.差热分析表明,随着Ga₂O₃含量的增加,锗酸盐玻璃的热稳定性增加.运用Judd-Ofelt(J_O)理论计算得到了Tm³⁺在不同Ga₂O₃含量的GeO₂-Ga₂O₃-Li₂O-BaO-La₂O₃玻璃中的J-O强度参数(Ω₂,Ω₄,Ω₆)及Tm³⁺各激发能级的自发跃迁概率、荧光分支比以及辐射寿命等光谱参量.在808nm激光二极管的激发下,测试并分析了Ga₂O₃对Tm³⁺荧光光谱特性的影响.随着Ga₂O₃从4mol%增加到16mol%,Tm³⁺在1.8μm处的荧光强度呈现先减弱后增强的特性.当Ga₂O₃含量大约在12mol%时,Tm³⁺在1.8μm处的荧光强度最弱,受激发射截面达到最小.还初步讨论了Ga₂O₃对玻璃结构与光谱参数的影响规律. 关键词： 3+掺杂锗酸盐玻璃')" href="#">Tm³⁺掺杂锗酸盐玻璃 光谱性能 Judd-Ofelt参数 热稳定性     

Synthesis and photoluminescence properties of MZr2(PO4)3:Eu3+; Bi3+ (M=Na; K) phosphors

A series of new red phosphors, MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K), were synthesized using the solidstate reaction method, and their photoluminescence spectra were measured. The MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors were efficiently excited by an ultraviolet (UV; 395 nm) source, and showed intense orange-red emission at 595 nm. Further investigation of the concentration-dependent emission spectra indicated that the MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors exhibit the strongest luminescence intensity when y = 0.01 in NaZr_2(0:95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ and y = 0.09 in NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺, whereas the relative PL intensity decreases with increasing Bi³⁺ concentration due to concentration quenching. The addition of Bi³⁺ widens the excitation band of NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ around 320 nm, which provides the useful idea of broadening the excitation band around 300–350 nm to fit the ultraviolet chip.     

Formation of highly textured (1 1 1) Bi2O3 films by anodization of electrodeposited bismuth films

Highly textured bismuth oxide (Bi₂O₃) thin films have been prepared using anodic oxidation of electrodeposited bismuth films onto stainless steel substrates. The Bi₂O₃ films were uniform and adherent to substrate. The Bi₂O₃ films were characterized for their structural and electrical properties by means of X-ray diffraction (XRD), electrical resistivity and dielectric measurement techniques. The X-ray diffraction pattern showed that Bi₂O₃ films are highly textured along (1 1 1) plane. The room temperature electrical resistivity of the Bi₂O₃ films was 10⁵ Ω cm. Dielectric measurement revealed normal oxide behavior with frequency.     

Bi离子掺杂GeO2-Al2O3-M(M=Na2O，BaO，Y2O3)玻璃的光学性质

用高温熔融法制备了Bi离子掺杂浓度为1mol%的GeO-B₂O₃-Na₂O (GBNB)，GeO₂-Al₂O₃-Na₂O(GANB)，GeO₂-Al₂O₃-BaO(GABB)和GeO₂-Al₂O₃-Y₂O₃(GAYB)玻璃.测定了样品玻璃的差热曲线、吸收、发射光谱及荧光衰减曲线.实验发现GBNB，GANB，GAYB，GABB的吸收边带逐步发生红移.由于这些吸收边带是由Bi³⁺的6s²电子到Bi⁵⁺ 6s⁰空轨道的跃迁引起.因此推断GBNB，GANB，GAYB，GABB玻璃中Bi⁵⁺离子的含量逐步增加.在GABB，GAYB，GANB三个样品中观察到发光中心约1220nm超宽带荧光发射.荧光强度从GABB，GAYB，GANB逐步减弱，荧光半高宽和荧光寿命逐步变小.这些超宽带的荧光归属为Bi⁵⁺离子的发光所致.从吸收与荧光光谱的变化，推断在GeO₂-Al₂O₃玻璃中引入BaO，Y₂O₃组分有利于Bi⁵⁺离子的形成.讨论了BaO，Y₂O₃化学组分对Bi离子在玻璃中的价态影响的内在机理. 关键词： 5+离子')" href="#">Bi⁵⁺离子 超宽带发光 吸收带 荧光寿命