Transparent Ceramics Research Articles

Al2O3 triggered in-situ crystallization of Gd3Al2Ga3O12 in glass and enhancement in magnetic and Faraday rotating properties

Nanocrystals doped transparent glasses or glass ceramics have shown promising tunable magnetic and magneto-optical performance. In this study, the Al2O3-induced in-situ crystallization of Gd3Al2Ga3O12 in tellurite glass was reported. 10–20 nm-cubic Gd3Al2Ga3O12 (Ia3d space group) nanocrystals formed in tellurite glass with Al2O3 content ≤ 0.75 mol% by 400 °C-heat treatment. When Al2O3 content in glass was higher than 0.75 mol%, excessive Al2O3 triggered the crystallization of orthorhombic GdAlO3 (Pnma) in which the Gd and Al ions existed as octahedral GdO8 and AlO6 units at a temperature higher than 398 °C. The in-situ crystallization influenced the glass network structure, broke the linkage of tetrahedral TeO4, and BO4, and formed trigonal pyramids TeO3 and BO3 instead. At the same time, nuclear magnetic resonance spectra revealed the conversion of AlO4→ AlO6, GaO4→ GaO6, and the changes from bridging oxygen to non-bridging oxygen as well. From energy-dispersive X-Ray analysis, Gd3+ clusters were observed, leading to the ferromagnetism of glass. Electron paramagnetic resonance spectra witnessed an enhancement of the Zeeman effect which is the reason for the improvement of Faraday rotation. Tellurite glass with 0.75 mol% Al2O3 after 400 °C-annealing (A75) showed a giant Verdet constant of 93 rad/T.m at 633 nm which is superior to most of the values from the literature.

Production and characterization of highly transparent novel magneto-optical Ho2Zr2O7 ceramics with anion-deficient fluorite structures

Based on material design idea, we employ a co-precipitation strategy to obtain sinterable Ho2Zr2O7 fluorite particles, successfully leading to novel transparent Ho2Zr2O7 ceramics with good optical/magneto-optical properties. The resulting precipitation precursor is identified to be hydrated basic carbonate upon calcination at the optimum temperature of 1250 °C into near-spherical Ho2Zr2O7 nanopowder with an average size of ∼64 nm and unimodal narrow size distribution. The crystal intrinsic oxygen defect in fluorite ceramic generally exists in the form of F+ center. The best bulk specimen achieved in this work exhibits a high refractive index of ∼2.1 and a high transparency of ∼74.4% at 1000 nm comparable with the corresponding defect-free single crystal (∼76.4% in theory). In the Ho2Zr2O7 structure system, the electronic polarizability of O2− anion generally remains constant around 2.2 Å3 in the visible region and the corresponding optical basicity is approximately 0.9. The developed magneto-optical transparent Ho2Zr2O7 ceramic has Verdet constants of -180 ± 3, -157 ± 5, -87 ± 2, -54 ± 2, and -43 ± 2 rad T−1 m−1 at 515, 635, 780, 980, and 1064 nm, respectively, which are roughly 1.2-fold higher than the commercial TGG crystal.

Superior Energy Storage Properties and Optical Transparency in K0.5 Na0.5 NbO3 -Based Dielectric Ceramics via Multiple Synergistic Strategies.

Eco-friendly transparent dielectric ceramics with superior energy storage properties are highly desirable in various transparent energy-storage electronic devices, ranging from advanced transparent pulse capacitors to electro-optical multifunctional devices. However, the collaborative improvement of energy storage properties and optical transparency in KNN-based ceramics still remains challenging. To address this issue, multiple synergistic strategies are proposed, such as refining the grain size, introducing polar nanoregions, and inducing a high-symmetry phase structure. Accordingly, outstanding energy storage density (Wtotal ≈7.5 J cm-3 , Wrec ≈5.3 J cm-3 ) and optical transmittance (≈76% at 1600nm, ≈62% at 780nm) are simultaneously realized in the 0.94(K0.5 Na0.5 )NbO3 -0.06Sr0.7 La0.2 ZrO3 ceramic, together with satisfactory charge-discharge performances (discharge energy density: ≈2.7 J cm-3 , power density: ≈243 MW cm-3 , discharge rate: ≈76ns), surpassing previously reported KNN-based transparent ceramics. Piezoresponse force microscopy and transmission electron microscopy revealed that this excellent performance can be attributed to the nanoscale domain and submicron-scale grain size. The significant improvement in the optical transparency and energy storage properties of the materials resulted in the widening of the application prospects of the materials.

Fabrication, microstructure and mid-infrared luminescence of Er:(ScxY1-x)2O3 transparent ceramics

Compositionally “mixed” (yttria-scandia) sesquioxide transparent ceramics doped with erbium ions, ∼7 at.% Er:(ScxY1-x)2O3 (where x = 0–0.445) were fabricated by vacuum sintering at 1750 °C for 5 h using 1.7 mol% ZrO2 as a sintering additive. For this, nanopowders of the same composition obtained by laser ablation and sedimentation were used. The as-prepared nanoparticles (monoclinic sp. gr. C2/m) had a mean size of 20 nm and they were transformed into the stable cubic phase by calcination at 870–1150 °C. The ceramics were of single-phase nature (C-type bixbyite structure, sp. gr. Ia-3). For the (Er0.074Sc0.114Y0.812)2O3 ceramic, the lattice constant was a = 10.5067 Å, the mean grain size – 21.6 μm, the average content of pores – 4.2 ppm and the transmission at 1.1 μm - 81.9%. The X-ray diffraction and Raman studies of ceramics confirmed the existence of a solid-solution composition. With increasing the Sc3+ content in the ceramics, their lattice shrinked, the mean grain size increased and the thermal conductivity decreased from 6.14 to 3.66 Wm−1K−1 at room temperature. The “mixed” ceramics exhibited intense inhomogeneously broadened emission around 2.8 μm making them promising for mid-infrared lasers.

Hybridization Engineering of Oxyfluoride Aluminosilicate Glass for Construction of Dual-Phase Optical Ceramics.

The construction of transparent ceramics under mild conditionsand standard atmospheric pressure has great scientific and technological potential; however, it remains difficult to achieve when conventional ceramic sintering techniques are used. Herein, a mild strategy for constructing dual-phase optical ceramics with high crystallinity (>90%) based on the stepped dual-phase crystallization of hybridized aluminosilicate glass is presented. Theoretical and experimental studies reveal that the hybridization of the glass system enables a new balance between the glass-forming ability and crystallization and can overcome the uncontrolled devitrification phenomenon during the dense crystallization of glass. Transparent hybridized oxide-fluoride ceramics with fiber geometry and dual-phase microstructures are also successfully fabricated. The generality of the strategy is confirmed, and transparent ceramics with various chemical compositions and phase combinations are prepared. Additionally, the cross-section of the ceramic fibers can be easily tuned into a circle, square, trapezoid, or even a triangle. Furthermore, the practical applications of optical ceramics for lighting and X-ray imaging are demonstrated. The findings described here suggest a major step toward expanding the scope of optical ceramics.

Fabrication and properties of highly transparent Er2O3 ceramics with ZrO2 additive by vacuum sintering

Highly transparent Er2O3 ceramics were fabricated at varied temperatures in the range of 1700–1850 °C for 8 h in vacuum environment using commercial Er2O3 powders as starting materials and 1 at.% ZrO2 as sintering additive, for the first time. The influence of sintering temperature on the microstructure and optical properties of Er2O3 ceramics was investigated. The Er2O3 ceramic sintered at 1850 °C had an average grain size of 6.2 μm and an in-line transmittance of 69% at 1100 nm, which reached the best transmittance level compared to the open literature. Therefore, the Er2O3 ceramic doped with 1 at.% ZrO2 as sintering additive developed in this study presented relatively smaller grain size and excellent optical quality, and could be a potential material for laser and photonic applications.

Fine-Grained Tb3Al5O12 Transparent Ceramics Prepared by Co-Precipitation Synthesis and Two-Step Sintering

In recent years, transparent terbium aluminum garnet (TAG) ceramics have attracted much attention for use in high-power Faraday isolators. Fine-grained ceramics usually possess better mechanical properties and accordingly better service performance. In this work, transparent TAG ceramics with fine grains were prepared using a two-step sintering procedure based on the low-temperature sintering process to suppress grain growth. The composition of TAG precursor and powders calcined at different temperatures was studied in detail. The microstructure and relative density of air pre-sintered TAG ceramics were studied to meet the requirements of hot isostatic pressing (HIP) post-treatment. Driven by the low pre-sintering temperature in air, the average grain sizes of the obtained TAG ceramics after HIP treatment are about 2.9–5.3 μm. The TAG ceramics (1.2 mm thick) pre-sintered at 1450 °C with HIP post-treatment at 1550 °C for 3 h under a 176 MPa Ar atmosphere possess the highest in-line transmittance of 80.3% at 1064 nm. The Verdet constant of the TAG ceramics at 632.8 nm is −180.5 rad·T−1·m−1 at room temperature, which is about 1.3 times larger than that of the commercial Tb3Ga5O12 single crystals.

Direct tape casting of Al2O3/AlN slurry for AlON transparent ceramic wafers via one-step reaction sintering

In this work, transparent aluminate oxynitride (AlON) ceramic wafers were successfully fabricated by the direct non-aqueous tape casting of Al2O3/AlN slurry and the one-step reaction sintering for the first time. The reaction sintered AlON ceramic wafer exhibits high transmittance of 73.2 % at the wavelength of 1600 nm. This fabricating route realizes smooth and flexible tape without cracks or pinholes in Al2O3/AlN system and efficiently shortens the preparation cycle of transparent AlON wafers, which is a feasible way to prepare high-quality transparent AlON ceramics with large lateral sizes and thin thicknesses by reaction sintering, might also promote the application of transparent AlON ceramic wafers.

Fabrication of engineered dopant profiles in Er/Lu:YAG transparent laser ceramics via additive manufacturing

Transparent ceramic Er:YAG laser rods were fabricated via the direct ink write (DIW) method with engineered doping profiles featuring an Er-doped core with endcaps and core-clad structures. Laser rods up to 11 cm in length were produced which required development of a scalable process. To achieve this, multiple improvements were implemented, including printing the rods horizontally on a substrate, rather than vertically, eliminating the need for an external support structure and using a sacrificial drying layer to mitigate warping and defects. Highly transparent rods were achieved with optical scatter levels as low as 0.5%/cm (at 543 nm). A small refractive index difference of 5.7 ppm was measured at the interface between the Er-doped core and the Lu-doped endcaps and cladding. These results demonstrate DIW as a straightforward method for making good optical quality laser rods with engineered doping profiles to improve laser performance.

Sm-Doped PIN-PMN-PT Transparent Ceramics with High Curie Temperature, Good Piezoelectricity, and Excellent Electro-Optical Properties.

Transparent piezoelectric materials are capable of coupling several physical effects such as optics, acoustics, electricity, and mechanical deformation together, which expands applications for mechanical-electro-optical multifunctional devices. However, piezoelectricity, transparency, and Curie temperature restrict each other, so it is difficult to achieve high piezoelectricity with both good transparency and a high Curie point. In this paper, Sm-doped 24Pb(In1/2Nb1/2)O3-42Pb(Mg1/3Nb2/3)O3-34PbTiO3 (PIN-PMN-PT) transparent ceramic with a high piezoelectric coefficient of 905 pC/N, excellent electro-optical coefficient of 814 pm/V, and high Curie-point of 179 °C is fabricated. Sm doping effect on the phase structures, piezoelectricity, ferroelectricity, optical transparency, electro-optical properties, and thermal stability is systematically investigated. Compared with PMN-PT transparent ceramics, PIN-PMN-PT transparent ceramics exhibit better temperature stability. Electro-optical modulation and energy conversion are achieved using PIN-PMN-PT transparent piezoelectric ceramic, which indicates that it has great potential to develop mechanical-electrical-optical multifunctional coupling devices for optical communication, energy harvesting, photoacoustic imaging, and so on.

Effect of R2O3 (R=Y, La) on the microstructure, optical, and photoluminescent properties of MgAl2O4:Cr3+ transparent ceramics

MgAl2O4:Cr3+ transparent ceramics were prepared by a hot-pressed sintering process with Y2O3 and La2O3 as sintering aids, and the effects on the microstructure, densification, optical transmission, and photoluminescent properties were investigated. The sintering aids of Y2O3 and La2O3 enhanced the relative density, reaching 99.33% with 2.4 wt% Y2O3 and 99.24% with 0.8 wt% La2O3. La2O3 also inhibited abnormal grain growth and obtained ceramics with uniform grain size. In addition, the optical transmission was also improved with Y2O3 and La2O3 as sintering aids. The transmission of the ceramic with 2.4 wt% Y2O3 exceeded 78% in the region of 700–6000 nm and reached 83% at 1450 nm. Moreover, Y2O3 and La2O3 both contributed to improving the quantum yield of the ceramics, especially for Y2O3, and the quantum yield was about 0.354, which was approximately two times higher than that without R2O3. In summary, La2O3 was helpful for improving sintering process, inhibiting grain growth, and homogenizing the grain size, while Y2O3 was significant for enhancing the optical and photoluminescent properties.

(Sr, Ca)AlSiN3:Eu2+ Phosphor-Doped YAG:Ce3+ Transparent Ceramics as Novel Green-Light-Emitting Materials for White LEDs.

In this work, based on Y3Al5O12:Ce3+ (YAG:Ce3+) transparent ceramic and (Sr, Ca)AlSiN3:Eu2+ phosphors, novel green-light-emitting materials were systematically studied. YAG:Ce3+ transparent ceramics with different doping-concentrations, from 0% to 1% (Sr, Ca)AlSiN3:Eu2+ phosphors, were fabricated by dry pressing and vacuum sintering. The serial phosphor ceramics had 533 nm green-light emission when excited by 460 nm blue light. The PL, PLE, and chromaticity performances were measured, indicating that more of the green-light component was emitted with the increase in doping concentration. The addition of (Sr, Ca)AlSiN3:Eu2+ phosphor increased the green-light wavelength area and improved the quantum yield (QY) of the YAG:Ce3+ ceramic matrix. The phase composition, microstructure, crystal-field structure and phosphor distribution of (Sr, Ca)AlSiN3:Eu2+ phosphor-doped YAG:Ce3+ transparent ceramics were investigated, to explore the microscopic causes of the spectral changes. Impressively, (Sr, Ca)AlSiN3:Eu2+ phosphors were distributed homogeneously, and the pinning effect of phosphor caused the suppression of grain growth. The novel materials could provide an effective strategy for full-spectrum white lighting and displaying applications in the future.

Optical properties and Faraday magneto-optical effects of highly transparent novel Tb2Zr2O7 fluorite ceramics

A novel magneto-optical transparent Tb2Zr2O7 ceramic with a high in-line transmittance of ∼76.2% at 635 nm (∼98.2% of the theoretical transmittance of perfect Tb2Zr2O7 single crystal) was successfully fabricated by vacuum sintering from its solid-phase reactive fluorite particle. In the visible region, the Tb2Zr2O7 bulk material was found to have a high refractive index of around 2.10 ± 0.03 and an optical basicity of 0.985 ± 0.015 while the electronic polarizability of the O2− anion in the Tb2Zr2O7 system generally remained constant at 2.45 ± 0.06 Å3. The Faraday effect results revealed that the transparent Tb2Zr2O7 ceramic had Verdet constants of −400 ± 4, −260 ± 4, and −62 ± 2 rad·T−1·m−1 at 515, 635, and 1064 nm, respectively, which were roughly 1.9-fold higher than the commercial Tb3Ga5O12 single crystal. Our outcomes demonstrated that the developed optical functional Tb2Zr2O7 ceramic has potential application as an excellent magneto-optical material.

Effect of reactive raw materials and pre-loading pressure on the microstructure and transmittance of pure CaF2 transparent ceramics

We reported an efficient way of fabricating pure CaF2 transparent ceramics using hot-pressing (HP) method. The effects of different reactive raw materials and pre-loading pressures on the microstructure and transmittance of pure CaF2 transparent ceramics were investigated. It was demonstrated that the optical quality of CaF2 ceramics was highly dependent on the reactive raw materials for synthesis of powders and pre-loading pressure. FESEM results manifested that the pre-loading pressure caused significant changes in the average grain size of pure CaF2 ceramics. With the pre-loading pressure increasing from 0 MPa to 15 MPa, the in-line transmittance of the obtained ceramics was obviously improved at all wavelength in the spectra. This work provides insight into mechanistic understanding of the sintering process of the fluoride-based ceramics and provides a reference value for improvement the optical quality of CaF2 transparent ceramics.

Micro-Nonuniformity of the Luminescence Parameters in Compositionally Disordered GYAGG:Ce Ceramics

The nonuniformity of the photoluminescence properties in a single grain scale of (Gd,Y)3Al2Ga3O12:Ce (GYAGG:Ce) ceramics was studied by scanning confocal microscopy and fluorescence lifetime imaging microscopy (FLIM). Oxide powders Gd1.5−xCexY1.5Al2Ga3O12 (x = 0.005, 0.015, 0.060) were fabricated by co-precipitation and thermally treated. Transparent ceramics samples were obtained in an oxygen atmosphere by pressureless sintering. With increasing Ce concentration in the composition, photoluminescence intensity at the grain boundaries decreases in comparison with the inner volume. Meanwhile, photoluminescence kinetics show the opposite behavior—slower at the grain boundaries and faster at the grain volume. These effects are found to be the most pronounced for the ceramic sample with a Ce content of 0.060 f.u. and are the consequence of an increase in the heterogeneity of the activator distribution at its high concentration in the ceramics. This observation set a limit in the Ce concentration in GYAGG:Ce garnet-type ceramics to reach the high-performing photo-luminescence features.

The effect of Y3+ doping upon Nd: S-FAP transparent ceramics for effective spectral performance improvement

In recent years, neodymium (Nd) doped transparent ceramics have played a great role as laser gain media. The ceramics with anisotropic structures have more advantages in luminescence. The Nd, Y co-doped Sr 5 (PO 4 ) 3 F (Nd, Y: S-FAP) nanoparticles were synthesized by a conventional chemical co-precipitation method. The transparent Nd, Y: S-FAP ceramics with high quality were fabricated by the hot-pressed sintering method. Moreover, the Judd-Ofelt (J-O) theory was adopted to further evaluate the spectral properties. The as-synthesized nanoparticles, whose grain size was about 25 nm, were nearly ellipsoidal. The highest transmittance of the ceramic was 2% Nd: S-FAP, reaching 85% at 1000 nm. The calculated absorption cross-section of the 4 I 9/2 → 4 F 5/2 + 2 H 9/2 transition from the measured absorption spectra was 4.58 × 10 −20 cm 2 . With the increase of the concentration of doped Y 3+ ions, the intensity of the emission peak at 1057 nm increased gradually. Moreover, the calculated stimulated emission cross-section of 4 F 3/2 → 4 I 11/2 transitions was 7.61 × 10 −20 cm 2 , which was greatly improved compared to the current matrix. The research, therefore, showed the great promise of Nd, Y: S-FAP as a solid-state laser.

Relying on energy transfer to enhance the 2.9 μm emission by co-doped Tm3+ ions in Dy:Y2O3 transparent ceramics

2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0, 0.1, 0.5 and 1) transparent ceramics were fabricated via vacuum sintering. The microstructural properties of the prepared ceramics were determined using XRD and SEM. The absorption cross-section of 2 at.% Tm, 1 at.% Dy:Y 2 O 3 ceramic was 0.53 × 10 −20 cm 2 with the FWHM of 43.59 nm. The increased cross-section originates from a large overlapping range appearing in the absorption spectrum of the Dy 3+ : 6 H 15/2 → 6 F 5/2 and Tm 3+ : 3 H 6 → 6 H 4 transitions. The J-O intensity parameters Ω 2 , Ω 4 and Ω 6 and the fluorescence characteristics of the pivotal luminescent level of the Dy 3+ ions were investigated. Under 793 nm excitation, the emission cross section of the Tm,Dy:Y 2 O 3 ceramic at 3094 nm was 3.63 × 10 −21 cm 2 with the FWHM of 355 nm. The fluorescence lifetimes of Dy 3+ : 6 H 13/2 level of 2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0.1, 0.5 and 1) ceramics were fitted to be 357 μs, 282 μs and 149 μs, respectively. In order to explore the quenching mechanism of Tm 3+ : 3 F 4 level, the fluorescence lifetimes of Tm 3+ : 3 F 4 of the 2 at.% Tm, xat.% Dy:Y 2 O 3 ceramics (x = 0, 0.1, 0.5 and 1) were measured to be 4.878 ms, 462 μs, 104 μs and 61 μs, respectively. The possible energy transfer mechanisms between Tm 3+ and Dy 3+ ions are discussed. The results show that adding Tm 3+ ions to Dy:Y 2 O 3 ceramics can effectively enhance the 2.9 μm MIR through energy transfer.

Negative lattice expansion-induced upconversion luminescence thermal enhancement in novel Na2MoO4:Yb3+, Er3+ transparent glass ceramics for temperature sensing applications

Negative lattice expansion-induced upconversion luminescence (UCL) thermal enhancement can efficiently solve thermal quenching of lanthanide ions, and the temperature sensing characteristics can be obtained by combining with fluorescence intensity ratio technology.

Enhancement of the photoluminescence modulation ratio in highly transparent KNN-based ceramics for optical information storage

The combination of high transmittance and large switching contrast in transmittance and photoluminescence intensity make the K0.5Na0.5NbO3–xPr ceramics promising for optical information storage and optical switch applications.

Preparation and properties of novel (Tb1−xCex)3Sc2Al3O12 magneto-optical transparent ceramics with different doping concentrations

(Tb1−xCex)3Sc2Al3O12 ceramics exhibited good optical quality and high Verdet constants, and were successfully prepared and optimised by Ce doping.