Growth and characterization of Yb doped garnet crystals for scintillator application

Several concentration of Yb-doped Lu₃Al₅O₁₂ (Yb:LuAG) and Lu₃Ga₅O₁₂ (Yb:LGG) single crystals were grown by the micro-pulling-down method. The crystals were seeded-grown in the 1 1 1 direction and transparent and crack free crystals were obtained. Photoluminescence spectra and decay kinetics of these crystals were studied. Charge transfer luminescence of Yb³⁺ was observed in both crystals. Mean decay time of about 25 ns at 90 K and strong thermal quenching at room temperature was measured for Yb 5%:LuAG. Radioluminescence intensity was compared to the standard BGO sample.     

Shaped single crystal growth and scintillating application of Yb:(Gd,Lu)3(Ga,Al)5O12 solid solutions

Shaped single crystals of (Yb_0.05Lu_xGd_0.95−x)Ga₅O₁₂ (0.0x0.9) and Yb_0.15Gd_0.15Lu_2.7(Al_xGa_1−x)O₁₂ (0.0x1.0) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)₃(Ga,Al)₅O₁₂ are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd³⁺ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd³⁺ or Yb³⁺ cations below 240 nm. A complete absence of Yb³⁺ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb³⁺ by that of Gd³⁺ ions. For specific composition of Lu_1.5Gd_1.5Ga₅O₁₂ an intense defect––host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi₄Ge₃O₁₂, was found.     

Luminescent and scintillation properties of Lu3Al5O12:Sc single crystal and single crystalline films

The work is dedicated to growth by the liquid phase epitaxy method and study of the luminescence and scintillation properties of Sc³⁺ doped single crystalline films (SCF) of Lu₃Al₅O₁₂ (LuAG) garnet. The scintillation properties of SCF are compared with single crystal (SC) analogues grown by the Horizontal Direct Crystallization and Czochralski methods. We consider the dependence of intensity of the Sc³⁺ emission in LuAG host on the activator concentration and influence of flux contamination on the light yield (LY) of the Sc³⁺ luminescence in LuAG:Sc SCF with respect to their SC counterparts and the reference YAP:Ce scintillator. From the NMR investigations of LuAG:Sc SCF we confirm the substitution by Sc³⁺ ions both the octahedral and dodecahedral positions of LuAG host and formation of the Sc_Al and Sc_Lu related emission centers, respectively. We also show that the luminescence spectrum in the UV range and decay kinetics of LuAG:Sc SCF can be effectively tuned by changing the scandium content.     

Growth and Luminescent Properties of NaGd(WO4)2:Yb3+ Crystals

Data are presented on the spectroscopic properties of Yb³⁺-activated NaGd(WO₄)₂, a disordered scheelite-like tungstate potentially attractive as a gain medium. NaGd(WO₄)₂:Yb³⁺ crystals are grown by the Czochralski technique. The polarized absorption and luminescence spectra and the luminescence decay kinetics of oriented samples with different Yb³⁺ concentrations are studied at 300 K. The gain coefficients are calculated for different populations of the upper lasing level 2F _5/2 of the Yb³⁺ ion.     

Crystal growth and structural particularities of (BaF2)1−x (Y,LnF3)x solid solutions

Highly transparent single crystals of (BaF₂)_1?x (Y,LnF₃)_x′ with Ln = Yb, Nd, are grown by the Bridgman technique. Lattice parameter variations are given, and the compensation by interstitial fluorine ions of the structure is verified from the crystal density.     

Nanoscale precipitation and mechanical properties of Al-0.06 at.% Sc alloys microalloyed with Yb or Gd

Dilute Al-0.06 at.% Sc alloys with microalloying additions of 50 at. ppm of ytterbium (Yb) or gadolinium (Gd) are studied with 3D local-electrode atom-probe (LEAP) tomography for different aging times at 300 °C. Peak-aged alloys exhibit Al₃(Sc_1−x Yb _x ) or Al₃(Sc_1−x Gd _x ) precipitates (L1₂ structure) with a higher number density (and therefore higher peak hardness) than a binary Al-0.06 at.% Sc alloy. The Al–Sc–Gd alloy exhibits a higher number density of precipitates with a smaller average radius than the Al–Sc–Yb alloy, leading to a higher hardness. In the Al–Sc–Gd alloy, only a small amount of the Sc is replaced by Gd in the Al₃(Sc_1−x Gd _x ) precipitates, where x = 0.08. By contrast, the hardness incubation time is significantly shorter in the Al–Sc–Yb alloy, due to the formation of Yb-rich Al₃(Yb_1−x Sc _x ) precipitates to which Sc subsequently diffuses, eventually forming Sc-rich Al₃(Sc_1−x Yb _x ) precipitates. For both alloys, the precipitate radii are found to be almost constant to an aging time of 24 h, although the concentration and distribution of the RE elements in the precipitates continues to evolve temporally. Similar to microhardness at ambient temperature, the creep resistance at 300 °C is significantly improved by RE microalloying of the binary Al-0.06 at.% Sc alloy.     

Up-conversion luminescence properties of Y2O2S:Yb,Er nanophosphors

Up-converting yttrium oxysulfide nanomaterials doped with ytterbium and erbium (Y₂O₂S:Yb³⁺,Er³⁺) were prepared with the flux method. The precursor oxide materials were prepared using the combustion synthesis. The morphology of the oxysulfides was characterized with transmission electron microscopy (TEM). The particle size distribution was 10–110 nm, depending on the heating temperature. According to the X-ray powder diffraction (XPD), the crystal structure was found hexagonal and the particle sizes estimated with the Scherrer equation agreeded with the TEM images. Upon the 970 nm infrared (IR) laser excitation, the materials yield moderate green ((²H_11/2, ⁴S_3/2) → ⁴I_15/2 transition) and strong red (⁴F_9/2 → ⁴I_15/2) luminescence. The green luminescence was enhanced with respect to the red one by an increase in both the crystallite size and erbium concentration due to the cross-relaxation (CR) processes. The most intense up-conversion luminescence was achieved with x_Yb and x_Er equal to 0.10 and 0.005, respectively. Above these concentrations, concentration quenching occurred.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Thermal Expansion and Electroabsorption in the TlInS2–TlYbS2 System

The thermal expansion and electroabsorption of TlIn_{1 – x} Yb _x S₂ solid solutions were measured as a function of temperature. The introduction of Yb into TlInS₂ was found to fully suppress the phase transition. It is shown that there is a perfect correlation between the band gap and thermal expansion of the TlIn_{1 – x} Yb _x S₂ solid solutions: both decrease with increasing Yb content. This finding is interpreted in terms of the effect of Yb substitution on bond strength.     

Yb-doped NaBi(WO4)2 fibre single crystals grown by the micro-pulling down technique and emission spectroscopic characterization

NaBi_1−xYb_x(WO₄)₂ fibres single crystals were successfully grown by micro-pulling down technology (MPD). The Yb³⁺-doped NaBi(WO₄)₂ fibres single crystals have been pulled using MPD technique with controlled diameter and stationary stable growth conditions corresponding to flat crystallization interface with meniscus length equal to the fibre radii and pulling rate range [6-48 mm h⁻¹]. We have determined the monophased field of NaBi_1−xYb_x(WO₄)₂ for x ≤ 0.3. The lattices parameters decrease as a function of Yb³⁺ substitution in Bi³⁺ sites. The melt behaviour has been study by DTA/TG analysis. We have found that the stoichiometric compounds NaBi(WO₄)₂ melt congruently at 935 °C. The fibre diameters varied from 0.5 to 1 mm depending on the capillary die diameter, pulling rate and the molten zone temperature. Complementary Yb³⁺ spectroscopic characterization in the NaBi(WO₄)₂ lattice has been done by IR emission measurements under laser pumping at room temperature.     

Spectroscopic properties of Yb3+-doped PbWO4 single crystal

Yb³⁺-doped PbWO₄ single crystal was grown using modified vertical Bridgman method. X-ray diffraction (XRD) analysis, optical absorption spectra, X-ray excited luminescence (XEL), fluorescence of ²F_5/2→²F_7/2 and its lifetime at room temperature were investigated. PWO:Yb³⁺ shows the broad absorption of Yb³⁺ (850–1050 nm) and efficient emission (950–1100 nm). Annealing exerts a distinct influence on the PWO:Yb³⁺ crystal, e.g. disappearance of color and annihilation of the absorption in the region around 450–750 nm, meanwhile the absorption of Yb³⁺ ions was enhanced by the annealing treatment. A novel luminescence band on the X-ray excited luminescence spectra of PWO:Yb³⁺ centered at about 500 nm was observed overlapped on that of PWO host.     

Yb<Superscript>3+</Superscript>-Activated inorganic aprotic liquids for diode-pumped lasers

This paper presents experimental data on the solubility of Yb(III) compounds in POCl₃–MCl _x , SOCl₂–MCl _x , and SO₂Cl₂–GaCl₃ binary aprotic solvents (where MClx is a Lewis acid). We have measured the absorption and luminescence spectra of Yb³⁺ in the solutions thus prepared. Liquid POCl₃–MCl₄–Yb³⁺ (M = Zr or Sn), SOCl₂–GaCl₃–Yb³⁺, and SO₂Cl₂–GaCl₃–Yb³⁺ gain media with [Yb³⁺] > 0.2 mol/L and an Yb³⁺ luminescence quantum yield η > 0.5 for diode-pumped lasers have been prepared for the first time.     

Optical and scintillation properties of SrI2:Yb2+

The luminescence and scintillation properties of SrI₂:0.5%Yb²⁺ have been investigated. SrI₂:Yb single crystals were grown by the vertical Bridgeman method from the melt. They showed a light yield of 38,400 ph/MeV and energy resolution of 12.5% for the 662 keV full absorption peak. Yb²⁺ photoluminescence intensity and decay time were studied between 78 and 600 K. Two emission bands centered at 418 and 446 nm were observed and ascribed to spin-allowed and spin-forbidden Yb²⁺ 5d-4f transitions, respectively. Their corresponding room-temperature decay time constants are 710 ns and 77 μs. Both, the emission intensities and the decay time constants vary with temperature. The obtained results were interpreted using a model of self-absorption of Yb²⁺ emission and a model of non-radiative relaxation of the electron from the low spin to the high spin 4f¹³5d Yb²⁺ excited states. The radiative lifetime of the low spin Yb²⁺ excited state was determined as 400 ns.     

Ca4REO(BO3)3 crystals for green and blue microchip laser generation: from crystal growth to laser and nonlinear optical properties

We have taken advantage of congruent melting behavior of the nonlinear rare-earth oxoborate Ca₄REO(BO₃)₃ family to perfect a process of collective fabrication of self-frequency doubling microchip laser based on Nd:GdCOB (Ca₄Gd_1−xNd_xO(BO₃)₃) crystals. The process goes from Czochralski boule to 1 × 3 mm² chips perfectly oriented (better than 0.1°) to the phase matching direction (θ=90°, φ=46°) in the XY principal plane, with dielectric mirrors directly deposited on both faces of the chips. 20 mW of self-frequency doubling output power at 530 nm was performed under 800 mW of diode laser as incident pump power at 812 nm. In addition, new compositions from the solid solution Ca₄Gd_1−xY_xO(BO₃)₃ (Gd_1−xY_xCOB) (x=0.13, 0.16, 0.44) have been grown by the Czochralski pulling method, in order to achieve noncritical phase matching (NCPM) second harmonic generation of ⁴F_3/2 → ⁴I_9/2 Nd³⁺ doped laser hosts. Three types of laser wavelengths have been chosen: Nd:YAP (YAlO₃) at 930 nm, Nd:YAG (Y₃Al₅O₁₂) at 946 nm, and Nd:ASL (Nd_ySr_1−x La_x−yMg_x Al_12−xO₁₉) at 900 nm. Angular acceptance measurements of these three types of compositions present very large values, compared to pure GdCOB or YCOB oriented in critical phase matching configurations.     

Energy transfer and luminescence studies of Pr, Yb co-doped lead borate glass

Lead borate glass samples doped with the tripositive lanthanide ions Pr³⁺ and Yb³⁺ were synthesized by the conventional melting-quenching method. The luminescence properties and energy transfer process from Pr³⁺ to Yb³⁺ were investigated. Upon ultraviolet excitation, the room temperature luminescence decay curve of a sample containing only a low concentration of Pr³⁺ exhibited monoexponential decay from ¹D₂ with the lifetime 37 μs, without emission from ³P₀. The room temperature Pr³⁺ emission intensity decreased with the increase of Yb³⁺ mole ratio in the glass. Under the excitation of 454.5 nm at 10 K, a broad red emission band centered at 605 nm, and an NIR emission band at 995 nm were observed in the co-doped lead borate glass, originating from Pr³⁺ and Yb³⁺ ions, respectively. The decay curves of the ¹D₂ emission from Pr³⁺ with addition of Yb³⁺ in lead borate glass show non-monoexponential character, and are best described by a stretched exponential function. The average ¹D₂ decay time decreases considerably with the addition of Yb³⁺ in the glass. Decay curve fitting using a modified Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Pr³⁺ to Yb³⁺, which is consistent with the expected cross-relaxation scheme. There is a good agreement of the estimated overall energy transfer efficiency obtained from the integrals under the normalized decay curves, or from the lifetimes fitted by the stretched exponential function, or from the average decay times.     

Up- and down-conversion luminescence in the oxyfluoride glass ceramics containing Ba2+1.5xYb1−xF7:Tb nanocrystals

Transparent oxyfluoride borosilicate glass ceramics containing Ba_2+1.5xYb_1−xF₇:Tb³⁺ nanocrystals were successfully prepared by a melt-quenching method with subsequent heat treatment. The precipitated crystalline phase in the glass matrix changed gradually from BaF₂ to Ba_2+1.5xYb_1−xF₇ with the increase of YbF₃ content, which was confirmed by the results of XRD, HRTEM and EDX measurements. The ultraviolet and visible up-conversion and near-infrared quantum cutting down-conversion emissions were observed and interpreted. These materials could be used to modify the solar spectrum and enhance the silicon solar cell efficiency by the up-conversion and down-conversion luminescence of Tb³⁺–Yb³⁺ couples in the oxyfluoride borosilicate glass ceramics.     

Growth and transport property measurements of rhenium doped tungsten diselenide single crystal

Single crystals of rhenium doped tungsten diselenide i.e. Re_xW_1−xSe₂ (x = 0, 0.0005, 0.001, 0.05, 0.1) are grown by vapour phase technique. The stoichiometry of grown single crystals is confirmed by energy dispersive analysis of X-rays. X-ray powder diffractograms obtained of these compounds were used for lattice parameter determination based on hexagonal system similar to that of host WSe₂.The crystallite size for each sample for different reflection is calculated using Scherrer's formula. Surface morphology as observed under optical microscope reflects that screw dislocation mechanism is responsible for growth of crystals. Electrical properties viz. Hall effect at room temperature, resistivity measurements at low temperature, and high pressure resistivity measurements indicates the semiconducting behaviour of Re_xW_1−xSe₂ (x = 0, 0.0005, 0.001, 0.05, 0.1) single crystals. Thermoelectric power measurements shows p-type nature of host WSe₂ whereas n-type nature of rhenium doped WSe₂ which matches with the results of Hall effect.     

掺Yb3+闪烁晶体的研究进展

掺Yb3+闪烁晶体是新近发展起来的一类闪烁体,有可能用于探测太阳中微子.本文简要介绍了掺Yb3+闪烁晶体的电荷迁移发光的机理以及基质晶体对温度猝灭与浓度猝灭的影响.综述了具有石榴石结构和钙钛矿结构的两类掺Yb3+闪烁晶体的研究进展,特别是YbYAG和YbYAP晶体的生长、闪烁性能以及应用前景.最后,对掺Yb3+闪烁晶体的未来研究方向做了展望.     

Growth and Spectroscopic Study of Yb3+-Activated YVO4 Crystals

The absorption and luminescence spectra of Yb³⁺ and the luminescence decay kinetics for the Yb^{3+ 2} F _5/2 level in YVO₄:Yb³⁺ crystals are studied. The luminescence cross section for the Yb^{3+ 2} F _5/2 ² F _7/2transition in YVO₄:Yb³⁺ is determined by the Füchtbauer–Ladenburg method, and the radiative lifetime of Yb³⁺ is evaluated.     

X-ray absorption study of rare earth ions in Sr2MgSi2O7:Eu,R persistent luminescence materials

The valence of the europium dopant and selected rare earth co-dopants (Ce³⁺, Dy³⁺, and Yb³⁺) in the Sr₂MgSi₂O₇:Eu²⁺,R³⁺ persistent luminescence materials were studied by room temperature XANES measurements. The results indicated the co-existence of both divalent and trivalent europium in all the studied materials. The relative amount of Eu³⁺ was observed to increase upon increasing exposure to X-rays, as expected by the persistent luminescence mechanism. This suggests a simultaneous filling of oxygen vacancies initially created by the reducing preparation conditions. For the Dy and Yb co-dopants, only trivalent species were observed. On the other hand, traces of tetravalent cerium were present in the Eu,Ce co-doped materials.