Terbium Aluminum Garnet Research Articles

Luminescence and energy transfer processes in Ce3+ activated (Gd,Tb)3Al5O12 single crystalline films

The luminescence and scintillation properties of gadolinium terbium aluminium garnet single crystalline films, Gd3−xTbxAl5O12, doped with Ce3+ are investigated as a function of the Gd/Tb ratio with the aim of an improved understanding of the energy transfer processes between Ce3+ and Tb3+ ions in the aluminium garnet hosts. Upon replacing the Gd3+ by Tb3+, the crystal field splitting for the 5d energy level of Ce3+ does not change significantly, due to comparable sizes of the Gd3+ and Tb3+ cations. Temperature dependence of the decay time of Tb3+ and Ce3+ luminescence confirms an efficient energy transfer from the Tb3+ to Ce3+ and provides a qualitative understanding of this process. Furthermore, bidirectional energy transfer processes between the Ce3+ and Tb3+ are revealed. Scintillation decays under α-particles excitation show the presence of the fast and slow sub-microsecond components.

Magneto-optical characteristics of holmium oxide (Ho_2O_3) ceramics

Transparent Ho2O3 ceramics are fabricated and their magneto-optical characteristics are reported for the first time, to the best of our knowledge. The value of the Verdet constant was measured in the 560–1064 nm wavelength range, and the value at 1064 nm is 46.3 rad/Tm. This corresponds to the Verdet constant for terbium aluminum garnet (TAG), which is ~1.3 times higher than that of terbium gallium garnet (TGG). The in-line transmittance at 1 μm wavelength is only ~60%, but the optical properties can be further improved by optimizing sintering conditions. This is a new potential magneto-optic material that can be applicable for high-average-power lasers.

Tb3Al2.5 Ga2.5O12 transparent ceramic for magneto‐optical application

AbstractThe optical quality and microstructure of the Tb3Al2.5 Ga2.5O12 transparent ceramic were investigated and compared with those of terbium gallium garnet (Tb3Ga5O12 TGG) and terbium aluminum garnet (Tb3Al5O12 TAG). The transmission of the Tb3Al2.5 Ga2.5O12 ceramic was as high as 80% in the visible and near‐infrared (IR) regions, which was close to the theoretical value. The Verdet constant of the Tb3Al2.5 Ga2.5O12 ceramic measured at 632.8 nm and room temperature was −150.6 rad/Tm, which was 12% larger than that of the TGG single crystal and 13% smaller than that of the TAG single crystal, and the Tb3Al2.5 Ga2.5O12 ceramic showed the highest transparency among these three samples.

Luminescence properties of Tb3Al5O12 garnet and related compounds synthesized by the metal organic decomposition method

The Tb–Al–O ternay compounds were prepared by the metal organic decompostion (MOD) method from mixted solutions of Al2O3 and Tb4O7 and subsequent calcination at Tc=1200°C in air. The structural and optical properties of the synthesized compounds were examined using X-ray diffraction analysis, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, PL decay kinetics, and diffuse reflectance spetrosopy. The stoichiometric compounds of terbium aluminium garnet Tb3Al5O12 (TAG) and peroviskite-type TbAlO3 were synthesized at molar ratios of x=0.375 and 0.5 [x ≡Tb4O7/(Tb4O7+2Al2O3)], together with the end-point binary materials of rhombohedral Al2O3 (α-Al2O3; x=0) and cubic Tb4O7 (x=1.0). One can also expect synthesis of stoichiometric compounds Tb4Al2O9 and Tb3AlO12 at x=0.667 and 0.75, respectively; however, these compounds were found to be very difficult to synthesize by the MOD method or, probably by other methods. Temperature dependence of the PL spectra for TAG was measured from T=20–440K in 10-K step and analyzed using a newly developed theoretical model. Raman scattering measurements were also performed on the Tb–Al–O material system with compositions widely varying from x=0 (α-Al2O3) to 1.0 (Tb4O7).

Fabrication, microstructure and magneto-optical properties of Tb3Al5O12 transparent ceramics

Terbium aluminum garnet (Tb3Al5O12, TAG) transparent ceramics were fabricated by the solid-state reactive sintering of a mixture of commercial Tb4O7 and α-Al2O3 powders with tetraethoxysilane (TEOS) and MgO as sintering aids. Samples sintered at 1700 °C and 1725 °C for 20 h were utilized to examine the phase compositions, optical quality, microstructure and magneto-optical property. X-ray diffraction (XRD) results show that the sample sintered at 1700 °C has a pure garnet crystal structure, while the characteristic diffraction peaks of TAG disappear when sintered at 1725 °C. The sample sintered at 1725 °C shows high transparency and the optical transmittance is beyond 80% in the region of 600–1500 nm. It is found that the sample sintered at 1700 °C exhibits homogeneous grains with the average size of about 5.97 μm, however, no TAG grains are observed in the sample sintered at 1725 °C. The Verdet constants of the samples sintered at 1700 °C and 1725 °C are −179.4, −179.3 rad T−1 m−1 at 633 nm, respectively. The thermal depolarization of the sample sintered at 1725 °C increases up to 2 × 10−4 at maximum laser power of 91 W, which corresponds to the isolation ratio of 37 dB.

Thermo-optical properties of terbium-aluminum garnet ceramics doped with silicon and titanium.

The Verdet constant and thermo-optical characteristics of a Si-doped and Ti-doped terbium aluminum garnet ceramics have been investigated. It is shown that the Verdet constant of the samples is ∼40% higher than that of TGG ceramics at 1064 nm. The best samples of Si:TAG have magneto-optical figures of merit more than 1.5 times greater than those of TGG ceramics. Si:TAG is better than TGG ceramics as a medium for high-power Faraday isolators.

Optical and magnetooptical properties of terbium–scandium–aluminum and terbium-containing (gallates and aluminates) garnets

Comparative measurements of the Faraday rotation in Tb3Ga5O12 (TGG) and Tb3Sc2–xAl3+хO12 (TSAG) garnets shows the values of the Verdet constant for TSAG are about 25% higher than that of TGG in the wavelength range 400–700nm at the temperatures T=95 and 300K. The increase of the Verdet constant is explained by increase of the “paramagnetic” frequency factor caused by the shift of the resonance frequency of the first allowed 4f→5d transition to the area of the lower frequencies in UV. The shift and observed strong broadening of the UV absorption bands in TSAG are explained by significant modification of the crystalline environment of the Tb3+ ion in this garnet. A comparison of the data of the C/D ratio in TSAG with the value of the magnetic moment of the Tb3+ ground state in Tb3Al5O12 (TAG) determined from magnetic measurements, showed an acceptable agreement for these parameters measured by fundamentally different methods. Measurements of the visible emission spectra reveal a strong influence of some disordering of the crystal field (CF) in TSAG in comparison with the terbium–aluminum garnet spectra. Magnetooptical effects of the intensity change of the luminescence lines in TSAG is caused by modification of the electronic structure of the 5D4 and 7F5 multiplets by Sc3+ ions in the lattice, leading to a local symmetry reduction of the Tb3+ ion in TSAG.

The temperature dependence of the thermo-optical properties of TAG optical ceramics

The thermal effects of thermally-induced depolarization and a thermal lens in terbium aluminum garnet (TAG) ceramics were investigated in the temperature range 79–293 K. Thermal effects decrease considerably upon cooling to 79 K, and it is demonstrated that the thermo-optical properties of TAG ceramics are not inferior to the properties of TGG ceramics. TAG is a promising medium for Faraday isolators and cryogenic Faraday isolators.

High Verdet constant of Ti-doped terbium aluminum garnet (TAG) ceramics

The temperature dependence of the Verdet constant of a 0.8 at % Ti-doped terbium aluminum garnet (TAG) ceramics was investigated using lasers with wavelengths of 632.8 and 1064 nm. A high value of the Verdet constant was obtained at 296 K – namely, 184 and 53 rad/Tm for 632.8 and 1064 nm, respectively. The Verdet constant of the Ti:TAG ceramics at 1064 nm is about 1.5 times higher than that of the terbium gallium garnet (TGG) ceramics. The transmittance of this sample was about 75% at the wavelength of 1 μm. This material represents a possible candidate for next-generation devices that utilize the magneto-optic effect.

Growth and properties of neodymium-doped terbium aluminum garnet crystal

Neodymium doped terbium aluminum garnet (Nd:TAG) crystal with dimensions of O30 × 90 mm was grown by the Czochralski method. The Nd:TAG crystal was characterized by X-ray diffraction, IR spectroscopy, absorption and fluorescence spectra, and laser performance test. The strongest absorption peak is located at 808 nm. There are 3 main fluorescence emission peaks located at 1062, 1108, and 1332 nm, respectively. The prepared 3 at % Nd:TAG crystal was pumped by InGaAs laser diode, the pumping threshold was 360 mW, the highest laser output was 310 mW, the light-light conversion efficiency was 32.3% and the slope efficiency was 51.7%.

Co-Precipitation Synthesis and Photoluminescence Properties of Ce<sup>3+</sup> Activated Terbium Aluminum Garnet (Tb<sub>1<i>-x</i></sub>Ce<sub><i>x</i></sub>)<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (0≤<i>x≤</i>0.05) Yellow Phosphors

Ce3+activated terbium aluminum garnet ((Tb1-xCex)3Al5O12, 0≤x≤0.05) phosphors have been converted from their precursors synthesized via co-precipitation from mixed solutions of aluminum and rare earth nitrates with ammonium hydrogen carbonate (AHC) as the precipitant. Detailed characterizations of the precursors and the phosphor oxides were performed by the combined techniques of X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetry/thermogravimetry (DSC/TG), and photoluminescence spectroscopy. The co-precipitated precursors possess a general composition of (NH4)x(Tb,Ce)3Al5(CO3)y(OH)z·nH2O, and the particles, having diameters of about 50nm, are well dispersed. Calcining the precursors at 1000°C for 4 h in the air and then reducing in a hydrogen atmosphere at 1000°C for 2 h yielded a phase pure garnet solid-solution of (Tb1-xCex)3Al5O12. The cubic lattice of garnet allows the Ce3+activators to reside at the dodecahedral interstitial sites. The resultant garnet phosphors with various Ce3+contents exhibit nearly identical positions of the PLE/PE bands, but significantly different intensities. Upon blue-light excitation at 470nm, the garnet phosphors exhibit broad band emissions peaking at 560nm. The garnet phosphors show a luminescence quenching concentration of 1.5at% for Ce3+.

High-power Faraday isolators based on TAG ceramics

The Faraday isolator based on a new magneto-optical medium--TAG (terbium aluminum garnet) ceramics was implemented and investigated experimentally. The magneto-optical element was temperature-stabilized using water cooling. The device provides a stable isolation ratio of 38 dB at 300 W laser power. Estimates show high performance of the device at a kilowatt laser power.

Fabrication of Magnetophotonic Crystals with Paramagnetic Garnet Films

We fabricated magnetophotonic crystals (MPCs) used in electric field driven magneto-optical spatial light modulators (e-MOSLMs) with a paramagnetic garnet, which is transparent in the blue wavelength region and has a sufficient Faraday rotation angle for several applications including hologram data storage, three-dimensional displays, and optical correlators. The e-MOSLM is composed of two dielectric mirrors and one defect layer comprising magneto-optic (MO) material and electro-optic (EO) material, which controls the localized wavelength due to the change in the refractive index. The e-MOSLM utilizing MPCs allows us to use thin film paramagnetic materials, i.e., a terbium gallium garnet (TGG) and a terbium aluminum garnet (TAG), instead of a rare-earth iron garnet (RIG) because the direction of magnetization does not need to be controlled in the MO layer. We fabricated TGG thin films and MPCs with the structure of a SGGG substrate/(Ta2O5/SiO2)6/TGG/(SiO2/Ta2O5)6 by rf-magnetron sputtering. The sample produced localized peaks in the photonic band gap of the transmission spectra and an enhanced Faraday rotation angle. These results indicate that e-MOSLMs comprising an MPC with a TGG defect layer can be useful devices at the blue wavelength.

A comparative study of the properties of terbium aluminum garnet powder sintered in air, vacuum and by laser irradiation

The structural and optical properties of terbium aluminum garnet (TAG) powder sintered (∼1100 °C) in air, vacuum (∼10 −6 mbar) and with 70 W of unfocussed CW CO 2 laser radiation, have been studied using X-ray powder diffraction (XRD), scanning electron microscopy (SEM/TEM), FTIR, optical absorption and photoluminescence techniques. Structural properties of TAG are found to be independent of the sintering procedure except that the pure TAG crystalline phase (Tb 3Al 5O 12) is evolved in about 2 h in the case of laser sintering compared to 8 h needed in air sintering (by furnace) and 4 h needed in the case of vacuum furnace sintering. On the other hand, the absorption/emission intensity (300–600 nm region) of TAG samples sintered in vacuum is higher compared to that of laser/furnace sintering in air.

Luminescence properties of phosphors based on Tb3Al5O12 (TbAG) terbium-aluminum garnet

The processes of excitation energy transfer in phosphors based on single-crystal Tb3Al5O12:Ce (TbAG:Ce) and Tb3Al5O12:Ce,Eu (TbAG:Ce,Eu) garnet films have been investigated. These films are considered to be promising materials for screens for X-ray images and luminescence converters of blue LED radiation. The conditions for excitation energy transfer from the matrix (Tb3+ cations) to Ce3+ and Eu3+ ions in TbAG:Ce and TbAG:Ce,Eu phosphors have been analyzed in detail. It is established that a cascade process of excitation energy transfer from Tb3+ ions to Ce3+ and Eu3+ ions and from Ce3+ ions to Eu3+ ions is implemented in TbAG:Ce,Eu via dipole-dipole interaction and through the Tb3+ cation sublattice.

Synthesis and photoluminescence properties of nanocrystalline terbium aluminium garnet phosphor

Nanocrystalline terbium aluminium garnet phosphor has been prepared by the calcinations (800-1600°C) of the precursor obtained by sol-gel technique. The particle size measurements and SEM analysis of the as prepared powder show the grain size variation in 50-600 nm range. XRD and FTIR measurements show the development of better crystalline phase with increase in the sintering temperature. Photo-luminescence spectra at room temperature consist of well separated six groups around 440 nm, 490 nm, 549.9 nm, 586.9 nm, 624 nm and 691 nm. The emission intensity of the group around 691 nm increases with the increase in calcination temperature from 1000°C-1400°C, while in case of all other groups the intensity decreases in this range of temperature.

Effects of BaF 2 flux on the properties of yellow-light-emitting terbium aluminum garnet phosphor powders prepared by spray pyrolysis

Spherical-like Tb 3Al 5O 12:Ce (TAG:Ce) phosphor powders with good photoluminescence intensities were prepared by spray pyrolysis from a spray solution containing BaF 2 flux. The phosphor powders prepared from the spray solution without the BaF 2 flux had irregular morphologies and aggregated structure. On the other hand, the phosphor powders obtained from the spray solution containing a high amount of BaF 2 flux were spherical-like shapes, narrow size distributions and non-aggregation. All the powders comprised single-phase body-centered cubic Tb 3Al 5O 12 (TAG), irrespective of the addition amount of the BaF 2 flux. The maximum photoluminescence intensity of the TAG:Ce phosphor powders obtained from spray solutions containing BaF 2 was 140% that of the phosphor powders obtained from the spray solution without the flux material. The mean size of the TAG:Ce phosphor powders prepared from the spray solution containing 9 wt.% BaF 2 with respect to the phosphor was 1.02 μm after post-treatment at 1450 °C.

Luminescence of Nanocrystalline Tb3Al5O12 : Ce3 + Phosphors Synthesized by Nitrate-Citrate Gel Combustion Method

-doped nanocrystalline terbium aluminum garnet (, ) phosphors were successfully synthesized in low temperature by nitrate-citrate gel combustion method using microwave irradiation as a heating source. The pure TAG phase was obtained after calcining at for . The prepared nanocrystalline phosphors showed a broad peak at , and the maximum doping concentration of for the highest emission intensity was at . The temperature dependence on photoluminescence properties of the prepared phosphors was investigated from , and the activation energies for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that prepared nanocryatalline has great potentials for a down-conversion yellow phosphor in white light emitting diodes.

Influence of additional Eu 3+ coactivator on the luminescence properties of Tb 3Al 5O 12:Ce 3+, Eu 3+

The luminescence properties of doubly activated terbium aluminium garnet samples were investigated in the present study. Commercial Tb 3Al 5O 12:Ce 3+ (TAG:Ce) shows the typical Ce 3+ ion luminescence of the allowed Ce 3+ d–f transition. Eu 3+ co-doping, however, reveals interesting results. In TAG:Ce, Eu, both Ce 3+ and Eu 3+ luminescence was measured at different Ce and Eu activator concentrations. The Ce 3+ ion can be used as a sensitizer in the TAG lattice that transfers its energy directly or via the Tb sublattice to the activator Eu 3+. The energy-level diagram was proposed to explain the luminescence mechanism. Application of TAG:Ce, Eu with improved chromaticity coordinates CIE (Commission Internationale de l’Eclairage) and color rendering index (CRI) in light emitting diodes (LEDs) is demonstrated.

Preparation of Cerium-Activated GAG Phosphor Powders: Influence of Co-doping on Crystallinity and Luminescent Properties

An impure-phase usually remains in the product of gadolinium aluminum garnet (GAG) powder as synthesized. In this study, an attempt to prepare a stable GAG pure-phase powder by substituting small cations (, , or ) at the dodecahedral sites or the substituting the large cation for the sites of the garnet structure was made. Pure garnet-phase GAG powder was formed by calcining at for . It was found that increasing the content in the lattice site of the dodecahedral or increasing the content in the site induces a blue shift in the emission wavelength. The color temperature of the pure (YAG:Ce) phosphor powder formed was lower than that of yttrium aluminum garnet and terbium aluminum garnet (TAG:Ce) phosphors.