Open Access Research Article Issue
Effect of Y substitution on the microstructure, magneto-optical, and thermal properties of (Tb1−xYx)3Al5O12 transparent ceramics
Journal of Advanced Ceramics 2024, 13 (4): 529-538
Published: 30 April 2024

Faraday isolators can prevent the front-end system from disturbance and damage caused by a back-reflected beam, so they are important elements in laser systems. As magneto-optical materials are the most important component in Faraday isolators, the studies on magneto-optical materials have attracted much attention these years. Tb3Al5O12 (TAG) ceramics are considered to be one of the most promising magneto-optical materials for visible to near-infrared wavelength band application because of their outstanding comprehensive magneto-optical performance. However, the optical quality of TAG ceramics needs further optimization to meet the application requirements. In this work, high optical quality (Tb1−xYx)3Al5O12 (x = 0, 0.05, 0.1, 0.2, and 0.3) magneto-optical ceramics were fabricated successfully by solid-state reaction sintering combined with hot isostatic pressing (HIP) post-treatment. All the ceramics obtained showed a single garnet phase for different values of x in the range studied. The addition of Y2O3 was found to suppress the secondary phase and improve optical quality significantly. The ceramic samples obtained had clear grain boundaries and possessed the in-line transmittance values of 82.9% at 1064 nm and 82.2% at 633 nm, respectively. The Verdet constants of (Tb1−xYx)3Al5O12 ceramics with x = 0, 0.05, 0.1, 0.2, and 0.3 were −188.1, −175.4, −168.5, −143.0, and −119.9 rad/(T·m), respectively. The thermal conductivity of TAG ceramics was found to be 5.23 W/(m·K) at 25 , and when 20% Y was substituted in place of Tb, the thermal conductivity decreased by only 9.4%.

Open Access Research Article Issue
Compositional regulation of multi-component GYGAG:Ce scintillation ceramics: Self-sintering-aid effect and afterglow suppression
Journal of Advanced Ceramics 2023, 12 (10): 1919-1929
Published: 25 October 2023

(Gd,Y,Ce)3(YxGa1−x)2GaAl2O12 (GYGAG:Ce) scintillation ceramics with different Y excess, where x = 0.005−0.08, were fabricated by the solid-state reaction method. The effects of stoichiometry on the phase composition, optical quality, and microstructure of GYGAG:Ce ceramics were analyzed. GYGAG:Ce ceramics have a pure garnet phase and obtain good in-line transmittance when x < 0.04, while more Y excess leads to the creation of the secondary phase. The change of x value influences the sintering behavior of the GYGAG:Ce ceramics: The excess of Y works as the self-sintering aid and significantly reduces the sintering temperature of ceramics. When x = 0.01–0.04, the X-ray excited luminescence (XEL) spectra and light yields of GYGAG:Ce ceramics are similar. The fast scintillation decay time and afterglow intensity of GYGAG:Ce ceramics show a slight decrease with increasing x value. Finally, additional 50–500 ppm MgO and 100–500 ppm CaO were introduced to the GYGAG:Ce ceramic with x = 0.04, and both were found to significantly increase the fast scintillation component and reduce the afterglow intensity by two orders of magnitude to 0.01% after X-ray cut-off.

Open Access Research Article Issue
Reactive SPS of Al2O3–RE:YAG (RE = Ce; Ce+Gd) composite ceramic phosphors
Journal of Advanced Ceramics 2023, 12 (5): 1015-1032
Published: 04 May 2023

Ultrafine-grained Al2O3–rare earth:yttrium aluminium garnet (Al2O3–RE:YAG) (RE = Ce; Ce+Gd) composite ceramics were obtained for the first time by reactive spark plasma sintering (SPS) using commercially available initial oxide powders. The effect of key sintering parameters (temperature, dwell time, and external pressure (Pload)) on densification peculiarities, structural-phase states, and luminescent properties of composites was studied comprehensively. Differences in phase formation and densification between Ce-doped and Ce,Gd-codoped systems were shown. Parameters of reactive SPS, at which there is partial melting with the formation of near-eutectic zones of the Al2O3–YAG system/coexistence of several variations of the YAG-type phase, were established. Pure corundum–garnet biphasic ceramics with an optimal balance between microstructural and luminescence performance were synthesized at 1425 ℃/30 min/30–60 MPa. The external quantum efficiency (EQE) of the phosphor converters reached 80.7% and 72% with close lifetime of ~63.8 ns, similar to those of commercial Ce:YAG materials, which is promising for further applications in the field of high-power white light-emitting diodes (WLEDs) and laser diodes (LDs).

Open Access Review Issue
A review on magneto-optical ceramics for Faraday isolators
Journal of Advanced Ceramics 2023, 12 (5): 873-915
Published: 19 April 2023

As a promising magneto-optical (MO) material applied in Faraday isolators, magneto-optical ceramics possess excellent comprehensive properties and have attracted much attention these years. Herein, we review the fabrication and properties of magneto-optical ceramics including garnet, sesquioxide, and A2B2O7 ceramics. Some of the ceramics have been proved to possess applicable performance, while further studies are still needed for most of the magneto-optical ceramics. Aiming at the application for isolators, the research status, existing problems, and development trends of magneto-optical ceramics are shown and discussed in this review.

Open Access Research Article Issue
Composition and luminescence properties of highly robust green-emitting LuAG:Ce/Al2O3 composite phosphor ceramics for high-power solid-state lighting
Journal of Advanced Ceramics 2023, 12 (3): 625-633
Published: 09 February 2023

The major advantage of laser lighting over white light-emitting-diode is the possibility to achieve ultra-high luminance. However, phosphors usually suffer laser-induced luminescence saturation, which limits the peak luminance of laser lighting devices. The aim of the present study is to develop LuAG:Ce/Al2O3 composite ceramics (LACCs) with a high saturation threshold for high-luminance laser lighting. Owning to the rigid crystal structure, proper synthetic process, and optimized thermal design, the LACCs possess small thermal quenching (16% loss in luminescence at 225 ℃), high quantum yield (> 95%), and excellent luminescence properties. When the LACCs are irradiated by blue laser diodes in a reflection mode, a high luminous flux of 4634 lm and luminous efficacy of 283 lm·W−1 are realized. Furthermore, they show no sign of luminescence saturation even when the power density reaches 20.5 W·mm−2. With these favorable properties, the designed LACCs show great potential in high-luminance laser lighting.

Open Access Review Issue
Development and prospects of garnet ceramic scintillators: A review
Journal of Advanced Ceramics 2022, 11 (12): 1825-1848
Published: 18 November 2022

Garnet ceramic scintillators are a class of inorganic scintillation materials with excellent overall performance. The flexibility of cation substitution in different lattice positions leads to tunable and versatile properties and a wide range of applications. This paper starts with an overview of the development history of the inorganic scintillation materials, followed by a description of major preparation methods and characterization of garnet scintillation ceramics. Great progress obtained in recent years consisting in applying the band-gap and defect engineering strategies to the garnet scintillation ceramics is reviewed. Finally, the respective problems in the preparation and performance of multicomponent garnet single crystals and ceramics and the effective solutions are discussed. The garnet scintillation ceramics with the highest application potential are summarized, and the future development directions are proposed.

Open Access Research Article Issue
Fabrication, microstructure, and properties of 8 mol% yttria-stabilized zirconia (8YSZ) transparent ceramics
Journal of Advanced Ceramics 2022, 11 (7): 1153-1162
Published: 02 July 2022

Fine grained 8 mol% yttria-stabilized zirconia (8YSZ) transparent ceramics with high optical and mechanical properties were fabricated by air pre-sintering and hot isostatic pressing (HIP) using commercial 8YSZ powders as the raw material. The pre-sintered ceramics with fine grains and appropriate relative density play a key role to achieve high transparency and suppressed grain size after HIP post-treatment at relatively low temperatures. With the increase of HIP temperature from 1350 to 1550 ℃, the in-line transmittance of 8YSZ ceramics at 600 nm increases from 56.9% to 71.5% (2.5 mm in thickness), and the average grain size increases from 2.4 to 16.3 μm. The corresponding bending strength of 8YSZ transparent ceramics decreases from 328±20 to 289±19 MPa, the hardness (H) decreases from 12.9±0.1 to 12.5±0.2 GPa, and the fracture toughness (KIC) decreases from 1.30±0.02 to 1.26±0.03 MPa·m1/2. Systematical investigations were carried out to study the combination of high optical transparency and excellent mechanical properties in 8YSZ ceramics.

Open Access Research Article Issue
Fabrication and properties of non-stoichiometric Tb2(Hf1–xTbx)2O7–x magneto-optical ceramics
Journal of Advanced Ceramics 2022, 11 (5): 784-793
Published: 02 April 2022

Non-stoichiometric Tb2(Hf1−xTbx)2O7−x (x = −0.07–0.45) magneto-optical ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) post-treatment without any sintering aids. The phase composition, densification process, microstructure, optical transmittance, and Verdet constant of Tb2(Hf1−xTbx)2O7−x ceramics were investigated. The in-line transmittance of (Tb0.93Hf0.07)2Hf2O7.07 ceramics with a thickness of 2.0 mm reaches 74.6% at 1064 nm. The Verdet constant of Tb2(Hf1−xTbx)2O7−x ceramics is −153.4, −155.8, and −181.2 rad/(T·m) at the wavelength of 633 nm when x = −0.07, 0, and 0.1, respectively. The Verdet constant increases with the increase of Tb content, and these values are higher than that of the commercial Tb3Ga5O12 crystal, indicating that non-stoichiometric Tb2(Hf1−xTbx)2O7−x ceramics have a great potential for the application in Faraday isolators.

Open Access Research Article Issue
Composition and structure design of three-layered composite phosphors for high color rendering chip-on-board light-emitting diode devices
Journal of Advanced Ceramics 2021, 10 (4): 729-740
Published: 05 August 2021

A three-layered phosphor structure was designed and prepared by the spin coating of BaSi2N2O2:Eu (cyan-emitting) and (Sr,Ca)AlSiN3:Eu (red-emitting) phosphor films on the yellow- emitting Y3Al5O12:Ce (YAG:Ce) phosphor ceramic synthesized by the solid-state reaction under vacuum sintering. In order to achieve high color rendering lighting, the influence of the composition and structure of the three-layered phosphors on the optical, thermal, and electrical properties of the chip-on-board (COB) packaged white-light-emitting diodes (WLEDs) was studied systematically. The WLED with the structure of "red+cyan+yellow" (R+C+Y) three-layered phosphor generated neutral white light and had a luminous efficacy of 75 lm/W, the fidelity index (Rf) of 93, the gamut index (Rg) of 97, and the correlated color temperature (CCT) of 3852 K. Under the excitation of laser diode (LD), the layer-structured phosphor yielded the white light with a luminous efficacy of 120 lm/W, color rendering index (CRI) of 90, and CCT of 5988 K. The result indicates that the three-layered phosphor structure is a promising candidate to achieve high color rendering and high luminous efficacy lighting.

Open Access Research Article Issue
Fabrication and performance evaluation of novel transparent ceramics RE:Tb3Ga5O12 (RE = Pr, Tm, Dy) toward magneto-optical application
Journal of Advanced Ceramics 2021, 10 (2): 271-278
Published: 24 February 2021

Transparent ceramics are at the heart of modern magneto-optical materials providing promising opportunities for Faraday isolators. 1.0 at% RE:Tb3Ga5O12 (rare earth (RE) = Pr, Tm, Dy) transparent ceramics were successfully prepared by air sintering and sequential HIP technique using the coprecipitated powders as the raw material. All the powders have shown to be a pure cubic terbium gallium garnet (TGG) phase and exhibit good dispersion. Additionally, a change could not be observed in particle shape with the different doped ions. After the two-step sintering, all the obtained ceramics have good optical quality, and the in-line transmittances at 1070 nm are higher than 80%. Moreover, no secondary phase can be detected from the microstructures. However, the pores which remain entrapped in the ceramics can be noted. The Verdet constant of ceramic samples is optimized by RE doping, and the Verdet constant at 632.8 nm is about -143 rad·T-1·m-1, which is about 5% higher than that of TGG ceramics. Finally, the thermo-optical properties of 1.0 at% RE:TGG transparent ceramics are compared. The annealed TGG ceramic showed the best thermo-optical properties, and the thermally induced depolarization of 1.0 at% Ce:TGG and 1.0 at% Tm:TGG was inferior to that of annealed TGG ceramic.

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