LuAG Research Articles

Synthesis of praseodymium doped lutetium and gadolinium aluminum garnets modified by scandium and boron to improve luminescence properties

The structural and luminescence properties of the Lu3Al4Sc1O12:Pr and Gd3Al3Sc2O12:Pr garnet scintillators co-doped with boron (B3+) ions were investigated. The addition of B3+ and Sc3+ to the structure has a positive effect on the luminescence properties, especially on the photo, radio emission intensities, quantum efficiency, and results in a reduction of the decay time, which is necessary for high-quality scintillators. Structural properties of garnets have been determined after X-ray diffraction analysis coupled with Rietveld refinement. Surface morphology analysis was performed using a scanning electron microscope and particle size was also determined. Elemental composition was confirmed by the ICP-OES technique. Reflection, excitation (in the UV and VUV range), emission (upon excitation by UV or X-rays), decay time, and quantum efficiency at room temperature were measured. Furthermore, the influence of temperature on excitation, emission, and decay curves was also analyzed. The obtained luminescence properties indicated positive effect caused by doping.

Light yield measurement of the Ce3+ activated LuAG nano-powder garnet scintillating detector

This paper focuses on the characterization of nano-powder (NP) scintillator, specifically presenting preliminary results of the measurement of the light yield (LY) of a newly synthesized Lutetium Aluminum (LuAG) garnet phosphor NP scintillator, doped with 0.1% cerium. The scintillation light yield was measured using the comparative method. Considering the light-scattering and self-absorbing properties of powder scintillators, alpha particles from 241Am source were used for excitation instead of Gamma/X rays, while a Ce3+ activated LuAG single crystal (SC) was employed as the reference detector due to its well-established light yield. A photomultiplier tube (PMT) served as the photodetector, and signals were read out by a nuclear instrumentation chain. The results demonstrate that the newly prepared LuAG:Ce NP exhibits a light output that is approximately 90% of that of the single crystal reference. These findings highlight the promising potential of NP scintillators as a viable alternative to single crystals, especially in applications where the preference for powder scintillators is evident.

Stoichiometric modulation and scintillation property characterization of Ce,Ca:LuAG ceramics

AbstractDue to the huge difference in the solubility‐product constants (Ksp) between the precipitates of Lu and Al, the synthesis of lutetium aluminum garnet (Lu3Al5O12, LuAG) nanopowders by coprecipitation method is prone to Lu loss, resulting in the creation of Al2O3 secondary phase. In this work, coprecipitated (Ce0.001Ca0.0015Lu(0.9975+x%))3Al5O12 (x = 0, 0.9, 1.2, 1.5) nanopowders with different starting stoichiometries are synthesized and combined with vacuum pre‐sintering and hot‐isostatic pressing to fabricate scintillating ceramics. The effect of compensated Lu content on the phase composition, microstructure, optical properties, and scintillation performance of ceramics is analyzed. The complete elimination of the secondary phase requires an additional compensation of 1.2% of Lu, which gives the best transmittance in ceramics. When x = 1.5, excessive Lu forms LuAl antisite defect, leading to the decrease of both light yield and intensity of the fast scintillation component.

Heat Capacity and Features of the Phonon Spectrum of Single Crystals of Solid Solutions of Yttrium–Lutetium Aluminum Garnets

The temperature dependences of the heat capacity were measured and the general patterns of the formation of the phonon spectrum of single crystals of solid solutions of yttrium-lutetium aluminum garnets Y3 – xLuxAl5O12 at 0 ≤ x ≤ 3 were investigated in the temperature range from 1.9 to 220 K. According to the data obtained at temperatures below 10 K, the Debye temperatures were calculated. The features of the phonon spectrum in the intermediate temperature range are interpreted as a superposition of optical modes for yttrium and lutetium garnets. It is shown that the low heat capacity values due to the contribution of acoustic phonons for Y2.25Lu0.75Al5O12 correlate with anomalies in the concentration dependences of the phonon transport, the absorption of acoustic waves, and the shape of the aluminum NMR line.

Yellow-white emitting phosphor-in-glass with LuAG:Ce and embedded CdS quantum dots

One-step sintering process was introduced to fabricate phosphor-in-glass (PiG) composite. Commercial cerium doped lutetium aluminum garnet (LuAG:Ce, Lu3Al5O12:Ce3+) phosphor was subjected to high-energy ball milling in a planetary ball mill. By controlling the milling time and velocity, the LuAG:Ce phosphors with average diameters from 0.5 to 10 μm was prepared. The effect of phosphor particle size on densification, final microstructure, thermal and optical properties of PiG was discussed. The results showed that the as-sintered PiG sample had amorphous phase and the LuAG:Ce phosphor particles uniformly distributed in glass matrix. LuAG:Ce particles were well preserved in silica glass matrix without any decomposition reaction. As the ball-milling process proceeded, the luminescent efficiency of phosphor was degraded owing to the low crystallinity of the surface of the LuAG:Ce particles. However, the sintering of LuAG:Ce with the glass and CdS QDs led to healing of the luminescence efficacy up to 23 % and shifting of chromaticity coordinates from green to yellow region. The improved value of correlated color temperature and the color rendering index of prepared PiG was achieved around 3100 K′ and 95, respectively. Moreover, the PiG with milled LuAG:Ce performs good laser output and can resist higher laser power owing to the effective heat dissipation.

Growth, Structure, Spectroscopy, and Laser Operation of a “Mixed” Yb:(Y,Lu)3Al5O12 Garnet Crystal

A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y0.601Lu0.233Yb0.166)3Al5O12 was grown by the Czochralski method and its structure, vibronic, spectroscopic, and laser properties were studied. The stimulated-emission cross-section for Yb3+ ions was maximized to 2.53 × 10−20 cm2 at 1031 nm. The emission bandwidth was ~8 nm, and the reabsorption-free luminescence lifetime of the 2F5/2 state was 1.063 ms. Pumped at 941 nm, the Yb laser generated a maximum output power of 1.04 W at 1.03 and 1.05 μm with a high slope efficiency of 76.4% and a laser threshold of 76 mW. A continuous wavelength tuning over a range of 51.6 nm (1026.4–1078.0 nm) was also achieved. Power scaling was achieved using a 969 nm diode-pumped microchip cavity. A maximum output power of ~9 W was obtained at 1.05 μm with a slope efficiency of 76% and an almost circular laser beam profile.

The effect of Pr3+ concentration on the microstructure, luminescence and scintillation properties of Pr:LuAG single crystals

High-quality lutetium aluminum garnet doped with various Pr3+ concentrations ((Lu1-xPrx)3Al5O12, abbreviated to Pr:LuAG) single crystals were grown by the optical floating zone method. The concentration of Pr3+ dependence on microstructure, luminescence and scintillation properties were systematically studied. Based on the results of Rietveld refinement, the doping of Pr3+ leads to lattice distortion and lowers its symmetry. The symmetry of the LuO8 dodecahedron center is lowest at 0.010, as confirmed by the Raman spectra. When excited at 450 nm and X-rays, the primary emission peak at 614 and 300 nm, respectively, induced by Pr3+ 4f2-4f2 and 4f5d-4f2 transitions. The optimal doping concentration is 0.010. The electric dipole-electric dipole interaction between adjacent Pr3+ was responsible for the concentration quenching in the Pr:LuAG single crystals. (Lu0.990Pr0.010)3Al5O12 shows the shortest average scintillation decay time (22.55 ns) and highest light yield (23,842 ± 2300 ph./MeV) under 662 KeV 137Cs gamma-ray irradiation. In terms of overall luminescence and scintillation performance, 0.010 doping was the best for Pr3+ doped LuAG single crystals.

3D Printing of LuAG:Ce transparent ceramics for laser-driven lighting

The fabrication of transparent ceramics with freely designed geometries via 3D printing represents a paradigm shift in molding processes. The application of luminescent transparent ceramics (LTCs) in high-power laser-driven solid-state lighting has been significantly limited by traditional molding methods. Herein, dense cerium activated lutetium aluminum garnet (LuAG:Ce) transparent ceramics with good light transmittance (∼40%) and complex structures were successfully fabricated using a digital light processing 3D printing method assisted by vacuum sintering. We developed an ink with a high solid content (∼50 vol%) and good shear thinning property, and the optimal dye content (0.002 wt%) and exposure dose (80 mJ cm−2) to achieve 50 μm high-resolution printing were determined. A superhemispherical ceramic device with a convex curvature radius (R) of 11 mm, a concave curvature radius (r) of 10 mm, and a thickness of 1 mm was printed and sintered, which exhibited excellent laser-driven lighting properties and a high laser fluence threshold (19.22 W mm−2) owing to the special structure of surface guide grooves formed by 3D printing. Optical components prepared using 3D-printed LuAG:Ce LTCs with excellent physical and chemical properties have promising applications in next-generation high-power laser-driven solid-state lighting devices.

Ce 3+:Lu 3Al 5O 12–Al 2O 3 optical nanoceramic scintillators elaborated via a low-temperature glass crystallization route

Transparent Ce:lutetium aluminum garnet (Ce:Lu₃Al₅O₁₂, Ce:LuAG) ceramics have been regarded as potential scintillator materials due to their relatively high density and atomic number (<i>Z</i>_eff). However, the current Ce:LuAG ceramics exhibit a light yield much lower than the expected theoretical value due to the inevitable presence of Lu_Al antisite defects at high sintering temperatures. This work demonstrates a low-temperature (1100 ℃) synthetic strategy for elaborating transparent LuAG–Al₂O₃ nanoceramics through the crystallization of 72 mol% Al₂O₃–28 mol% Lu₂O₃ (ALu28) bulk glass. The biphasic nanostructure composed of LuAG and Al₂O₃ nanocrystals makes up the whole ceramic materials. Most of Al₂O₃ is distributed among LuAG grains, and the rest is present inside the LuAG grains. Fully dense biphasic LuAG–Al₂O₃ nanoceramics are highly transparent from the visible region to mid-infrared (MIR) region, and particularly the transmittance reaches 82% at 780 nm. Moreover, Lu_Al antisite defect-related centers are completely undetectable in X-ray excited luminescence (XEL) spectra of Ce:LuAG–Al₂O₃ nanoceramics with 0.3–1.0 at% Ce. The light yield of 0.3 at% Ce:LuAG–Al₂O₃ nanoceramics is estimated to be 20,000 ph/MeV with short 1 μs shaping time, which is far superior to that of commercial Bi₄Ge₃O₁₂ (BGO) single crystals. These results show that a low-temperature glass crystallization route provides an alternative approach for eliminating the antisite defects in LuAG-based ceramics, and is promising to produce garnet-based ceramic materials with excellent properties, thereby meeting the demands of advanced scintillation applications.

Широкополосная ЭПР-спектроскопия кристалла Lu-=SUB=-3-=/SUB=-Al-=SUB=-5-=/SUB=-O-=SUB=-12-=/SUB=-:Tb-=SUP=-3+-=/SUP=-

In a single crystal of lutetium aluminum garnet (Lu3Al5O12, LuAG) in the frequency range of 37–210 GHz, at a temperature of 4.2 K, the EPR spectra of non-Kramers Tb3+ impurity ions were recorded. The measurement results indicate that Tb3+ ions replace Y3+ ions in the dodecahedral position with local D2 symmetry. The value of the g factor, the hyperfine structure constant, and the energy interval between the ground and the first excited nondegenerate sublevels of the ground multiplet are determined. Weak satellite signals were also registered, the origin of which is associated with the formation of antisite defects in the environment of paramagnetic Tb3+ centers.

Wide-band EPR spectroscopy of a Lu-=SUB=-3-=/SUB=-Al-=SUB=-5-=/SUB=-O-=SUB=-12-=/SUB=-:Tb-=SUP=-3+-=/SUP=- crystal

In a single crystal of lutetium aluminum garnet (Lu3Al5O12, LuAG) in the frequency range of 37-210 GHz, at a temperature of 4.2 K, the EPR spectra of non-Kramers Tb3+ impurity ions were recorded. The measurement results indicate that Tb3+ ions replace Y3+ ions in the dodecahedral position with local D2 symmetry. The value of the g factor, the hyperfine structure constant, and the energy interval between the ground and the first excited nondegenerate sublevels of the ground multiplet are determined. Weak satellite signals were also registered, the origin of which is associated with the formation of antisite defects in the environment of paramagnetic Tb3+ centers. Keywords: hyperfine interaction, rare earth ions, spin Hamiltonian, non-Kramers ion.

A highly efficient and broadband near-infrared-emitting garnet phosphor for plant lighting realized by cation co-substitution in lutetium aluminum garnet

Near-infrared phosphor-converted light emitting diodes (NIR pc-LEDs) is developing rapidly in plant cultivation because of its low cost, compact size and high efficiency. The NIR light of 700 ∼ 760 nm is known to be beneficial for seed germination and growth. Therefore, the exploration of NIR phosphors with specific wavelength and high efficiency is essential for the development of high-performance plant cultivation pc-LEDs. In this study, a highly efficient and thermal stable Cr3+ doped Lu2CaAl4SiO12 (LCAS) phosphor with broadband NIR emission covering phytochrome Pfr absorption range was successfully realized via Ca2+-Si4+ co-substitution of Lu3+-Al3+ pairs. The LCAS:0.07 Cr3+ exhibits a major emission peak of 740 nm with a FWHM of 160 nm and its internal/external quantum yield (IQY/EQY) is as high as 80%/30.5%. The integrated emission intensity of LCAS:0.07Cr3+ at 423 K lost only 33.8% of its initial intensity, indicating that it has a good thermal stability. When the LCAS:0.07Cr3+ was packaged into a pc-LED with a driving current of 320 mA, the device output power and photoelectric efficiency reached 90.6 mW and 8.6%, respectively, demonstrating that this phosphor has potential application in plant cultivation lighting.

Ho:LuAG single crystal fiber: growth, spectroscopy and laser characteristics.

Lutetium aluminum garnet single-crystal fiber (SCF, ∼ Φ 0.9 mm - 165 mm) doped with 0.5 at.% Ho3+ has been grown by the micro-pulling-down (µ-PD) technique. The room-temperature absorption and emission spectra exhibit similar features to the bulk crystal. Laser performances of the SCFs with two different pump configurations, i.e., pump guiding and free-space propagation, are studied by employing a 1.9-µm laser diode and a high-brightness fiber laser, respectively. Laser slope efficiencies obtained with both pump configurations can be higher than 50%, and a maximum output power of 6.01 W is achieved at ∼ 2.09 µm with the former pump. The comparable efficiency to the high-brightness pump is an indication of that high laser performance can also be expected through pump-guiding in the SCF even with a low pump beam quality.

Determination of different garnet films characteristics prepared via sol-gel spin or dip-coatings techniques

In order to convert high-energy radiation, such as gamma or X-rays, into a visible light, a certain type of material is needed. Such compounds are usually referred to as scintillators. Over the years many different candidates to fit the requirements were examined. However, compounds with garnet structure have attracted a particularly large amount of attention. Cerium doped yttrium and lutetium aluminum garnets (YAG:Ce, LuAG:Ce), have high density, high thermal stability, a rather intensive emission/excitation and high quantum efficiency which are needed for a good scintillator. However, further optimization and improvement is still needed especially on the shortening of the decay time. One way to approach this problem is to alloy the aforementioned compounds with different elements, such as boron or magnesium.

Comparative study of LuxY1-xAG (x=0..1) laser ceramics doped with 5% Yb3+

Materials with high thermo mechanical properties are required as laser media for high-powered lasers. One of such materials is lutetium-aluminum garnet (LuAG) doped with ytterbium. In the present work, we discuss for the first time a full comparative study of 5% Yb-doped LuYAG ceramics with variation Lu/Y ratio. Samples were prepared with addition of B2O3, MgO and SiO2 which were used as sintering aids. Grain sizes, shrinkage curves, lattice constants and transmission spectra were measured for all samples. Thermal conductivity was measured in a wide temperature range for all studied samples. Output power of 12 W and 60% slope efficiency were obtained on the 5% Yb:LuAG disk laser.

Comparative study of Yb (3+) doped LuYAG laser ceramic: optical, structure and lasing properties

Materials with high thermo mechanical properties are required for high powered lasers. One of such materials is lutetium-aluminum garnet (LuAG) doped with ytterbium. In this work main properties of (LuxY1-x)AG:Yb3+ ceramics with x=0-1 are studied in order to determine optimal Lu/Y ratio for lasing purposes.

Manipulation of brightness and decay kinetics of LuAG: Ce3+ and YAG: Ce3+ by simple metal oxides in polymeric matrices

In this work, light-induced interactions among commercially available green and yellow garnets and wide range opto-emitters of ZnO and CuO have been investigated in terms of excitation, emission and decay kinetics. When the lutetium aluminum garnet (LuAG: Ce3+) is encapsulated along with the nanocrystalline metal oxides in a polymethylmethacrylate (PMMA) matrix, the absorption and emission efficiency of the phosphor enhanced 59-fold compared to its additive-free form. Similarly, when yttrium aluminum garnet (YAG: Ce3+) was incorporated with ZnO and ZnO-CuO nanoparticles, the composites exhibited 6- and 4-fold enhancement in the emission intensities, when excited by the blue light. In parallel to the emission intensities, the external quantum yield (EQY) of LuAG:Ce3+-ZnO-CuO enhanced from 88.4 to 116.4%, with respect to the additive-free-LuAG:Ce3+. Similarly, in YAG:Ce3 + based samples, the presence of the ZnO in the composite resulted in the enhancement of the EQE from 80.6 to 98.1.The steady-state and decay time based experimental studies have confirmed that metal oxides act like donors and phosphors as acceptors when encapsulated in a polymeric matrix at a critical concentration. The decay time of the LuAG: Ce3+ increased from 181to 397 microseconds when embedded along with the ZnO-CuO in the PMMA matrix. Similarly, the decay time of the YAG: Ce3+ extended from 49 to 477 microseconds for the YAG: Ce3+-ZnO composite films.

Influence of boron on the essential properties for new generation scintillators

Cerium doped yttrium aluminum (YAG:Ce) and lutetium aluminum garnets (LuAG:Ce) are some of the most popular materials used as scintillators. While the scintillators themselves are materials that absorb and convert high-energy radiation into light. The decay time in YAG:Ce and LuAG:Ce is about 60 ns, therefore the essential task for their improvement would be to shorten it as much as possible. For this reason, in this work, the aforementioned garnets were doped with different amounts of boron. B3+ ion has a suitable neutron capture cross section and can therefore absorb gamma radiation. Because of the extremely strong absorption of thermal neutrons and the weak interaction with MeV gamma rays the material is an exciting new inorganic scintillator candidate for the detection thermal and epithermal neutrons. B3+ stimulates and improves the absorption of such radiation. In the study, 0.05% of cerium and different amounts of boron doped YAG, YLuAG (Y1.5Lu1.5Al5O12) and LuAG were synthesized by the sol-gel method. To investigate the influence of the annealing atmosphere, all samples in powder form were heated either under air or reducing atmospheres. XRD, SEM characterization techniques were performed on the synthesized samples. Luminescent properties were measured and analyzed. The main results that have been observed from this research were that boron does indeed shorten decay time, while also increasing emission intensity. The most intensive emission was of those powder compounds containing 1% and 5% of boron, regardless of the annealing atmosphere. While pure samples doped with 5% of boron have the shortest decay times.

Optical characterization of Y3Al5O12 and Lu3Al5O12 single crystals

In this work spectrally dependent optical parameters of nominally pure single crystals of yttrium aluminum garnet (YAG) and lutetium aluminum garnet (LuAG) were studied using spectroscopy ellipsometry together with transmittance measurements in a broad spectral range from 0.73 to 6.42 eV (193–1700 nm). Obtained data in terms of complex refractive index and reflectivity represent an extension of previous studies towards the ultraviolet spectral region and provide a background for the design of a variety of optical applications such as laser host matrix systems, doped luminescence materials, optical imaging devices for semiconductor immersion lithography, construction of scintillators and other devices operating in the ultraviolet spectral region. A complete database of obtained optical parameters (real and imaginary parts of complex refractive index) in the whole spectral range is included in the supplementary part.

Luminescence and up-conversion of single crystalline Lu3Al5O12:Pr3+

This work deals with the spectroscopic properties of praseodymium doped single crystalline lutetium aluminum garnet (LuAG:Pr3+). A special focus was set on temperature- and time-dependent spectroscopy. Beyond the well-known down-conversion luminescence of LuAG:Pr3+, also UV-A/B up-conversion luminescence under excitation with a 488 nm laser was thoroughly investigated. Furthermore, the results of the spectroscopic investigations on the single crystalline material were supplemented and compared with measurements on a microscale powder sample.In addition, to the spectroscopic investigations, mechanistic considerations are presented to obtain a closer look at the up-conversion process in LuAG:Pr3+. We promote the thesis of a temperature-dependent energy transfer up-conversion mechanism.