In this work, 5at.% Yb:Lu2O3 transparent ceramics were air-annealed at different temperatures to eliminate oxygen vacancies for laser performance improvement. The influence of annealing temperature on microstructures, optical quality, and laser performance was investigated comprehensively. The ceramics HIP (Hot isostatic pressing) post-treated at 1750°C and annealed above 1100°C show a significant optical quality decrease due to residual pore expansion, and the ceramic sample annealed at 900°C shows better laser performance than others. The maximum output of 2.88 W was obtained at 1033.3 nm with a slope efficiency of 37.4% under a quasi-continuous wave (QCW) mode. Note that 5at.% Yb:Lu2O3 transparent ceramics HIP post-treated at 1550°C still keep good transparency even when being annealed at 1300°C due to less residual compressed pores. The highest slope efficiency is about 73.8% with a maximum output power of 2.84 W under QCW. Fine-grained and dense Yb:Lu2O3 transparent ceramics could be annealed at higher temperatures to eliminate oxygen vacancies more thoroughly to improve laser performance.

Defect-free Y2O3 transparent ceramics is an interesting material which is used for IR windows, nozzles or laser host, etc, due to its mechanical and optical properties, high thermal and chemical stability, and high melting point. To achieve full densification and the absence of pores, sintering aids are used. For yttria ceramics, the optimal choice is ZrO2. It has a significant influence not only on transmittance, but on the other characteri-stics of the material as well. For high transparency, ceramics has to remain single-phase, thus forming a solid solution of Y2O3 and ZrO2, but the solubility limit isn't studied in detail. Therefore, the presented work aims to investigate the solubility limit of ZrO2 in yttria ceramics and the dependence of properties on the concentration of sintering aid. Ceramics samples with a concentration of ZrO2 of 0-11 mol% were obtained by uniaxial and cold isostatic pressing (CIP) followed by vacuum sintering at 1735 °C for 22 h. The SEM and XRD analysis, refractive index and transmittance measurements were performed. No secondary phases were observed in analysed samples by SEM, which indicates the formation of a solid solution and full solubility of ZrO2 in the analysed range of concentration. Also, it was found that even 3 mol% of ZrO2 significantly improve the microstructure of samples. It allows for the elimination of residual porosity due to full densification during sintering. Also, the grain size decreased from 14 ?m for pure Y2O3 to 3.8-6.1 ?m for samples with 3-11 mol% of ZrO2. XRD analysis showed that the phase composition did not change between samples with 0 and 11 mol% of sintering aid. Decreasing of lattice parameters with increasing of ZrO2 amount was observed due to the replacement of Y3+ ions in the lattice by the smaller Zr4+. A steady increase of refractive index was observed with increasing Zr content. Obtained results allow us to conclude, that the solubility limit of ZrO2 in Y2O3 was not reached within the studied range and that the presence of ZrO2 improves ceramics properties. In the next step, optical transmittance was analysed. Among all obtained Y2O3:Zr4+ ceramics the highest transmittance (78.60% at 1100 nm at a thickness of 2.11 mm) was achieved for the sample with 7 mol.% of ZrO2.

Transparent ceramics stand as cutting-edge class of materials that benefit from the shaping possibilities of ceramic technology and from the crystalline structure that offers superior performance compared to glasses. Transparency may be obtained only when the material is free of defects that scatter light, viz. pores or secondary phases. Mostly, this means a requirement of a fully dense, single-phase, defect-free microstructure. However, the impact of small scatterers on transparency diminishes as their size decreases, allowing the development of multiphase materials, composites, that are transparent in the IR and even in the visible range for nanometric grain sizes. Conversely, another important topic in the field of transparent ceramics are macroscopic composites. The increasing optical quality of transparent ceramics in the past years has ignited a growing interest, especially in optics and photonics [1]. Transparent ceramics stand as counterparts to more traditionally used single crystals, which may have the same composition, but are obtained by different processes, mostly based on growth from melt. This process is time- and energy-consuming, and above all imposes significant limitations on the final shape of the components, which is obtained by machining. Transparent ceramics, in contrast, take advantage of the shaping flexibility of ceramic processing, in particular to produce composite or gradient structures without the need of post-processing and bonding [2]. Unlike the nanocomposites mentioned above, these composites are macroscopic, mostly with relatively small differences in chemical composition among the different parts. In the case of simple shapes and planar interfaces such structures may be obtained by diffusion bonding of polished single crystals, but the process is demanding and expensive. Ceramic processing allows us to shape such structures in the green state with a high degree of freedom, avoiding intermediate cutting, polishing and bonding steps. The aim of the presentation is to illustrate the possibilities and benefits of transparent ceramics with a particular emphasis on multimaterial components, spanning both nano- and macro-composites. The application potential will be illustrated on specific examples involving structures for lasers or protective domes and the shaping possibilities will be discussed. References [1] J. Hostasa, "Ceramics for laser technologies", pp. 110-124 in Encyclopedia of Materials: Technical Ceramics and Glasses - Vol. 3. Ed. M. Pomeroy, Elsevier, 2021. [2] F. Tian et al., J. Eur. Ceram. Soc., 42 (2022) 1833-1851.

Transparent ceramics represent both a symbol of perfection in the world of ceramics, given the necessity to produce materials without defects or porosity, as well as of new possibilities, in particular for harsh environments and high-power laser applications. These materials, with a fully crystalline, single-phase structure and the production flexibility offered by the ceramic processing technologies, represent a new generation of materials for optics and photonics and have been in the spotlight of R&D in the past decade. Zenit Smart Polycrystals is a startup, born as a spin-off of the National Research Council of Italy, founded with the aim to offer new components for the laser, optics, and photonics markets. And the novelty comes from the implementation of additive manufacturing in the production process. Thanks to the flexibility and high precision of shape and composition distribution within a single component, it is possible to disrupt the laser and photonics scene going beyond the technology based on single crystals, i.e. providing near-net-shape components with complex structures produced in one single shaping step, skipping high precision post-polishing and bonding. New tailor-made laser gain media will be offered to materials processing, automotive as well as medical markets.

Optical Y2O3 ceramics are actively researched as a multifunctional material and found wide practical application due to its mechanical and optical properties, chemical and thermal stability. This material should be possibly defect-free since the presence of pores deteriorates its optical and mechanical properties. Therefore, the choice of raw materials and the study of the effect of processing methods are fundamental. This work aims to study the influence of the initial powders and their milling conditions on the characteristics of Y2O3 transparent ceramics. The morphology and sintering behavior of four different commercial Y2O3 powders after milling under different conditions was investigated. 3 mol.% ZrO2 was used as a sintering aid. The samples were compacted by uniaxial pressing and CIP, and sintered in air at 1600°? for 4 h or in vacuum at 1735°C for 32 h. Firstly, the powders after milling at 80 rpm for 22 h were analysed. All studied powders were characterized by different values of specific surface area, particle size and agglomeration, which influenced densification. Among all samples obtained by sintering in air, only one provided a high density and uniform microstructure, and was thus used for further studies. Influence of milling conditions on powders parameters and properties of vacuum-sintered Y2O3 ceramics was determined. We found that 300 rpm for 65 min is optimal for obtaining powders with high sinterability. The specific surface area of this powder is 21.3 m2/g, and the average particle size is 480 nm. Decreasing of milling speed leads to an increase in the particles size. An increase in the milling time to 10 h is accompanied by an agglomeration of particles. Y2O3 vacuum-sintered ceramics were characterized by a relative density of 100% and transmittance of 78.1% (1100 nm). Acknowledgments: The authors are grateful to the JECS Trust for funding (Contract No. 2021293).

??????? ???????? ?? ?????? ?????? ????? ??????? ????????????? ?? ?????????????????? ????????. ??????? ????? ?????????? ? ???????? ????????????, ???????? ? ????????? ???????????? Y2O3 ???????? ????????? ?????? ????????? ???????????? [1]. ? ??????? ????????? ????? ???????? ??????? ??????? ??????? ????????? ??????. ????????? ???????? (???) ???????? ??????? ? ????????? ??????????? ?????????. ? ??'???? ? ???, ????? ???????? ?????????? ? ??????????? ?????? ?????? ?? ??????? ???????? ??????? ???? ? ??????? ????????? ???????? [2]. ????? ?????? ? ??????????? ?????? ???????? ???????? ? ???? ?? ??????? ?? ??????? ??????????? ???????? Y2O3. ? ????? ?????? ???? ?????????? ?????????? ???????? ??????????? ???????? ?????? ????? (Nippon, Stanford, Solvay ? US RN) ????? ?????? ??? ?????? ??????. ? ?????? ???????, ?? ?????? ????????, ???? ?????? 3 ???.% ZrO2. ??????, ????????????? ?????????? ? ???????? ???????????? ???????????, ??????? ?? ??????? ??? ??????????? 1600 °? ???????? 4 ???. ?? ? ??????? ??? 1735°? ???????? 32 ???. ?? ??????? ????? ?????????? ?????????? ???????? ????? ??????????????????? ?????? (80 ??./??. ???????? 22 ???.). ????? ????????????? ???????? Stanford ???????????????? ????????? ??????? ? ???????? ???????????, ??? ?? ?????????? ??? ??????????. ?????????? ????? ???????? ????? ?????????, ?????????? ????? ?? ???????? ? ?????? ?'???. ????? ???? ???????, ????????? ????????? ?? ???????, ???? Nippon-???????? ???????????????? ??????? ????????? ? ?????????? ??????????????? ? ??????????? ????????? ???????? ??????? ??????????? ????? ??????? ???????? (???) ?? ??????? ????????. ?????? ???????? ????? ???????? ???????? Solvay ? US RN ?????????? ?? ????? ??????????????? ? ??????? ????????????? ??????? ??????????? ??????????. ????? ?????, Nippon Y2O3 ???? ?????? ??? ????????? ??????????. ????????? ????? ???? ?????? (????????? ? ???) ?? ????????? ??????? ? ??????????? ????????-???????? ???????? Y2O3. ??????????? ?????????? ????? ????????? ???????? ? ??????? ?????????? ?? ???????? (300 ??./??., 65 ??.). ?? ????? ???? ?????? ????? ???????? ???????? 21.3 ?2/?, ? ???????? ?????? ???????? ??????? 480 ??. ???????? ????????? ?????? ?? 200 ? 100 ??./??. ?????????? ?? ?????????? ??????? ????????, ? ?????????? ???? ?????? ?? 10 ??? ??????????????? ???????????? ???????? ????? ?????? ???????? ??????? ????? ????????. ???????? Y2O3, ???????? ? ????? ??????? ??????? ?????????? ???????? ??? 1735 °? ???????? 32 ???, ???????????????? ??????? ????????? ????????? 100±0,5% ? ???????? ???????? ???????????? ????? ???? ??????????????? ??????? (78,1 % ??? 1100 ??, ?? ??????? 95,6 % ??? ???????????? ????????). ??????????? ???????? ?? ????????? CNR-ISSMC (?????? CNR-ISTEC), ??????, ?????? ? JECS Trust (???????? No. 2021293) ??????????: [1]J. Kong, D.Y. Tang, J. Lu, et al, Appl. Phys. 79, 449-455 (2004). [2]S. Hríbalova, W. Pabst, J. Eur. Ceram. Soc. 41, 2169-2192 (2021)

Ceramic Yb:YAG is a suitable gain medium candidate for high-energy lasers. The use of a combination of TEOS and MgO sintering aids led to uniform microstructure independently on the increase of thickness. Samples were thoroughly characterised.

Planar polycrystalline laser waveguides with the structure YAG/Yb:YAG/YAG were produced by ceramic processing. Transparent ceramics represent a valid alternative to single crystals as the flexibility of the ceramic process paves the way to new application opportunities. The implementation of different ceramic shaping techniques allows the production of complex or multicomponent (composite) structures that are generally difficult or about impossible to obtain with single crystals. A practical example are the planar structures presented here, characterized by a strict control of the dopant distribution obtained already during the shaping process, without further machining or bonding. The waveguides are composed of a laser active Yb:YAG layer obtained by tape casting with a thickness between 100 and 250 ?m placed between dopant-free YAG cladding obtained by oxide powder mixing. The refractive index of Yb:YAG is higher than YAG thus realizing a multimode waveguide. Two types of geometries were tested: 1. simple planar waveguide with a sandwich structure (confinement in one direction); 2. waveguide with a rectangular cross section (confinement in two directions). The waveguides were tested for laser emission in a cavity end pumped by a fiber coupled diode laser, under quasi-CW pumping conditions (rectangular pump pulses with 10 ms duration, 10 Hz), delivering up to 60W at 936 nm. The planar waveguide has shown a maximum output power of 14.4 W (slope efficiency 39.1%, optical efficiency 27.4%) whereas the 2D waveguide had a maximum output power of 11.6 W (slope efficiency 38.4%, optical efficiency 22.4%). Lasing wavelength was 1030 nm.

Transparent ceramics are an emerging class of materials with interesting optical and scintillating properties accompanied by a relative easiness of the production method: the easy and flexible shaping makes ceramics technology extremely appealing, especially when a specific geometry is not achievable via single crystal growth, such as multilayer structures for scintillation and laser operation [1]. In the present work, we design a novel layered Y3Al5O12:Pr/Gd3Ga3Al2O12:Ce (YAG:Pr/GGAG:Ce) composite scintillating ceramic, consisting of a two-phase mixture with different luminescent activators, prepared by a combined approach of conventional pressureless sintering in air followed by hot isostatic pressing. The layered morphology efficiently combines the well-known physical and luminescence properties of YAG [2] with the newly found outstanding performances of GGAG [3]. The doping with Pr3+ and Ce3+ ions provides a bright luminescence and a fast scintillation response of the order of tens of nanoseconds. Indeed, RE ions emitting in well-distinguished spectral regions allow to selectively identify the scintillating layer interacting with the ionizing radiation, with profound implications for phoswich applications and particle discrimination in mixed radiation fields [4]. In addition, the tunable geometry of the layered structure opens perspective for the improvement of the spatial resolution in positron emission tomography with depth-of-interaction scanners [5]. 1.Z. Hu et al., J. Am. Ceram. Soc., 100, 5593 (2017) 2.A. Ikesue et al., Nat. Photonics, 2, 721 (2008) 3.J. Zhang et al., J. Eur. Ceram. Soc, 37, 4925 (2017) 4.G. Zorloni et al., Radiat. Meas., 129, 106203 (2019) 5.K. Shimazoe et al., Nucl. Instr. Methods Phys. Res. A, 873, 12 (2017)

Yttrium oxide (Y2O3) optical ceramics, pure or doped with rare earth ions, are currently investigated as a promising material for transparent windows, solid-state lasers or refractory components. Y2O3 combines high melting point, transparency in a wide wavelength range, good thermal and optical properties and excellent mechanical and chemical stability. There are several approaches to produce transparent yttria ceramics by using hot pressing (HP), hot isostatic pressing (HIP), spark plasma sintering (SPS), microwave sintering, or vacuum sintering. Sintering using high pressures (HP, HIP, SPS) allows decreasing the consolidation temperature and recrystallization rate due to considerable activation of volume diffusion and creep. However, the high cost of the equipment and significant operational expenses restrict the application of sintering under high pressures. An alternative approach to fabricate Y2O3 transparent ceramics is sintering without applying high pressures, such as vacuum sintering. In order to increase sintering activity and reduce consolidation temperatures, very fine powders (submicron- to nanopowders) with high surface energy are required. The powder characteristics (particle size, morphology or specific surface area) determine the sintering behavior and, as a consequence, the possibility and conditions required for the achievement of transparency of ceramics. However, it should be noted that the effect of different starting powders on the processability of Y2O3 transparent ceramics has not been studied in detail in the current literature. This project is focused on the powder treatment of Y2O3 and the production of transparent ceramics: a number of commercial powders with suitable morphology will be selected for the study of the effect of milling parameters on the morphology and sinterability of the powders, eventually with the use of sintering aids. The proposed activities plan includes: 1.Characterization and selection of starting Y2O3 powders (determination of their morphology by SEM, specific surface area, etc.); 2.Milling tests: study of the variation of process parameters (milling speed and time, milling media size); 3.Characterization of the milled powders; 4.Shaping of powders by pressing and sintering in vacuum; 5.Characterization of sintered ceramics (optical properties, microstructure). Depending on the results (transmittance) and the time available, the use of a sintering aid may be considered for one selected powder. The aim of this study is to provide practical information related to the selected powders, and to make more general considerations, linking the microstructure and the type of defects in the sintered ceramics to the process parameters and powder characteristics.

Abstract: YAG-based transparent ceramics are conventionally prepared by vacuum sintering or by a double sintering process, viz. vacuum sintering followed by Hot Isostatic Pressing (HIP). The use of a pressure-assisted process on vacuum pre-sintered ceramics favours the closure of residual porosity, and is therefore suitable for the production of highly transparent ceramics, where pores would otherwise act as light scattering centres. On the other hand, these post-sintering treatments are effective with samples exhibiting a suitable microstructure after vacuum sintering, i.e. no secondary phases and only closed pores with a size smaller that the size of the grains. As an alternative to HIP, a fast post-sintering treatment with Spark Plasma Sintering (SPS) is proposed. In this poster we present a comparison of transparent YAG-based transparent ceramics obtained by vacuum sintering followed by post sintering with HIP and with SPS. Several combinations of vacuum sintering + HIP/SPS conditions were tested on YAG and Yb:YAG samples prepared by reactive sintering of single oxides in order to modify their microstructure, especially grain size and residual porosity. Magnesium oxide (M) or magnesium oxide with TEOS (M+T) were used as sintering aids. SEM and optical microscopy analyses were used to characterise the microstructure of the samples after vacuum sintering and after post-sintering, and to identify correlations between the microstructure and optical properties of transparent YAG ceramics. Acknowledgements: F. P. gratefully acknowledges the financial support of JECS TRUST.The authors from CNR ISTEC gratefully acknowledge the support from the Italian Ministry of Defence under PNRM Contract No. 8731 of 04/12/2019 (CeMiLAP²).

Abstract: Fluoride sintering additives are frequently utilized for the densification of various ceramics, but the current comprehension of the mechanism by which they affect densification is lacking behind empirical experience. A prominent example is LiF, which is commonly used in the preparation of transparent ceramics (MgAl2O4, Y2O3, YAG, MgO). It is generally accepted that LiF melt allows the rearrangement of particles, enhances densification and later in the process escapes from the system due to its high vapor pressure, so ideally no secondary phase is present in the final product. However, the second - and the most essential - step of enhanced densification is a source of scientific dispute. It is not clear if oxygen vacancies are responsible for this enhancement and if so, under what circumstances are they created. The present work tries to shed more light on fluoride additives and how they work throughout the whole process of preparation. The results suggest that the mutual dissolution of sintering additive and the base ceramic is the key aspect. Acknowledgements: This work was supported from the grant of Specific university research - grant No. A1_FCHT_2022_002

Yttrium aluminum garnet (Y3Al5O12) has an isotropic crystal structure that makes it transparent to visible and IR electromagnetic radiation even in polycrystalline ceramic form. Only fully dense and defect-free materials can be transparent. Typical defects in ceramics are pores and secondary phases, both acting as scattering centers lowering the transparency. A common method to produce YAG ceramics is the solid-state reaction sintering under high vacuum of Y2O3 and Al2O3 powders mixed according to the YAG stoichiometry. We compared different powder treatments to identify the process that leads to the least quantity of defects in reaction-sintered YAG ceramics. We tested the effect of a series of modifications in the powder treatment process, starting from a preset combination of Y2O3 and Al2O3 powders. For example, ultrasonication was used to evaluate its ability to break the powders aggregates. Spray drying was used to dry the powders after the ball milling step, and compared to other drying processes. Finally, the use of a dispersant to favor an intimate powder mixing was also investigated. The obtained powders were pressed, calcinated and sintered in a high vacuum furnace. The samples were mirror polished on both the faces, characterized by SEM and by measuring the optical transmittance. A novel approach was adopted to measure the volumetric residual porosity with a digital optical microscope. The amount and size of residual pores are measured in an automatic way by assembling together a subsequent set of pictures taken at different depths.

The efficiency of using the collector pressing scheme in the Spark Plasma Sintering (SPS) process has been confirmed in improving the optical, physical, and mechanical properties of yttria-stabilized zirconia (YSZ) ceramics with an increased shape factor. An approach for developing a seal surface and determining the optimal method of increasing pressure and temperature during SPS on this surface was used to optimize the consolidation modes of the materials. It has been shown that transparent/translucent YSZ ceramics with an increased shape factor (14 mm in diameter and up to 5 mm in height, h/d = 0.36) can be successfully fabricated by the SPS technique combined with the collector pressing scheme. The optical properties and microhardness of ceramics obtained using the collector scheme are better to the optical properties of ceramics obtained using the conventional uniaxial pressing scheme.

ISTEC R&D activities span from the fundamental understanding of the process-microstructure-property correlations, to the materials functionalization through suitable procedures, up to the validation of demonstrators in relevant environment.

Transparent Yb:Y3ScAl4O12 (Yb:YSAG) ceramics with different ytterbium doping concentrations such as 5, 10, 15, 20 at.% have been successfully fabricated by solid-state reactive sintering. All the obtained ceramics are in dense and homogeneous structure after sintering at 1820 degrees C for 30 hours and with a posttreatment by hot isostatic pressing at 1750 degrees C for 3 hours with 200 MPa pressure. We systematically analyzed the influence of Yb3+ doping concentration on the microstructure and optical properties of the ceramics. The 10 at.% Yb:Y3ScAl4O12 ceramics with a thickness of 3.2 mm show the best transparency as high as 80.9% at 1100 nm. The laser emission of the 10 at.% Yb:YSAG ceramics was tested, resulting in a maximum slope efficiency of 67.6% and a maximum output power of 11.3 W under quasi-continuous wave pump conditions. The tuning range spanned from 990 to 1071 nm.

Transparent 4 at.% Tm:Y3ScAl4O12 (Tm:YSAG) laser ceramics were fabricated by solid-state reaction combined with vacuum sintering method. The 4 at.% Tm:YSAG ceramic sample sintered at 1800 degrees C for 30 hours possesses homogenous microstructure and excellent optical properties, showing a transmittance of 79.3% at 2000 nm. The absorption and emission spectra of the Tm:YSAG ceramics are studied and compared with those of 4 at.% Tm:Y3Al5O12 ceramics. The introduction of Sc3+ greatly affects the energy levels of the Tm3+, causing the disappearance and degeneration of some absorption and emission peaks in the middle infrared region. The laser performance of the 4 at.% Tm:YSAG ceramics is also tested in the Quasi-continuous-wave (QCW) mode by pumping with a 790 nm laser diode (LD). A maximum laser output power of 0.54 W with a slope efficiency of 4.8% is achieved, which is the first laser output for Tm:YSAG ceramics.

In recent years, oxide materials based on garnet structure are being investigated as very promising candidates in the field of scintillation because of their high density, good chemical stability, optical transparency, and the possibility to easily incorporate luminescent rare-earth ions. Several studies demonstrated that garnet crystals show high light yield and advantageous timing performances, which make them of interest for applications in medical imaging and high energy physics detectors [1]. Among synthetic garnets, Ce-doped gadolinium gallium aluminum garnet (GGAG:Ce) is a relatively new and interesting material. It is a mixed garnet that has displayed very good scintillation and luminescence properties: its high density enhances the interaction with ionizing radiation, and the presence of Gd provides a high cross section for thermal neutron capture [2]. GGAG:Ce preserves a crystalline cubic structure, which allows to produce it in the form of transparent polycrystalline ceramic [3] with favorable characteristics for optical applications such as lasers, LEDs, and scintillators. In this work, ceramic samples were produced by reaction sintering from commercial oxide powders: the mixed powders were pressed into pellets and sintered by a combined process of air sintering and hot isostatic pressing. The sintering process was carefully selected and the use of sintering additives was optimized to eliminate porosity, which is crucial to achieve a good optical transparency. Optical properties were studied by means of optical absorption spectroscopy, steady-state and time resolved photo- and radio- luminescence, and correlated to the fabrication process parameters. Moreover, trapping phenomena caused by the presence of point defects were investigated by wavelength resolved thermally stimulated luminescence in a wide temperature range (10 - 800 K); a significant persistent luminescence signal was also singled out and investigated as a function of temperature. The presence of point defects was also evidenced by the occurrence of a sensitization of the radio-luminescence signal as a function of increasing cumulated X-ray dose, related to a competitive process between traps and Ce recombination centers in free carrier capture. Finally, preliminary results on recently developed layered Y3Al5O12:Pr/Gd3(Ga,Al)5O12:Ce (YAG:Pr/GGAG:Ce) ceramics for particle detection and discrimination will be also reported. This work has been supported by H2020 European Institute for Innovation and Technology (EIT) SPARK project (16290) and H2020 Rise project INTELUM (644260). [1] M. T. Lucchini et al., Nucl. Instrum. Methods Phys. Res. A 816 (2016) 176-183 [2] J. Dumazert et al., Nucl. Inst. Methods Phys. Res. A 882 (2018) 53 [3] Y. Ye et al., Opt. Mater. 71 (2017) 23

Densi ceramici trasparenti a base Cr:YAG sono stati preparati tramite sinterizzazione in vuoto (a 1735°C o 1750 °C per 16 ore). Sono stati testati vari parametri del processo di produzione: composizione chimica (additivi di sinterizzazione), omogeneizzazione, essicamento, sinterizzazione e annealing. Si presenta un metodo che ha portato alla trasmittanza di 73.75 % a 1400 nm su uno spessore del campione di 1.134 mm e densità di 4.55 g/cm3. I campioni preparati sono stati caratterizzati tramite microscopia elettronica a scansione (SEM), la loro densità è stata misurata con il metodo di Archimede. Sono stati misurati gli spettri di trasmittanza dei campioni trasparenti. Si mostra l'effetto del processo di trattamento delle polveri (omogeneizzazione, essicamento) alla trasparenza dei ceramici ed è presentata una combinazione di questi parametri idonea per la produzione di materiale trasparente. Un tentativo è stato fatto per l'aumento della conducibilità termica del Cr:YAG tramite l'aggiunta di particelle metalliche (tungsteno, molibdeno) oppure di nitruro di alluminio prima della sinterizzazione. Le particelle metalliche non hanno resistito all'ossidazione durante la fase di annealing, mentre il nitruro di alluminio non ha resistito al processo di sinterizzazione. Tuttavia, l'approccio presentato può essere uttilizzato per un tipo di ceramici YAG che non richiede la fase di annealing dopo la sinterizzazione.

We demonstrated highly efficient laser emission of a 6% at. Yb:(Lu,Y)2O3 ceramic sample with formula (Yb0.06Lu0.12Y0.78Zr0.04)2O3 (i.e. Yb doped solid solution of Y2O3 and Lu2O3 with Zirconia as sintering aid) fabricated by means of solid-state sintering of mixed sesquioxide nanoparticles under vacuum. The ceramics features a very good optical quality, with a transmission very close to the theoretical limit. The spectroscopic characteristics were investigated, resulting in intermediate properties between Yb:Y2O3 and Yb:Lu2O3. Laser emission was obtained under diode pumping at 936 nm, in CW and quasi-CW pumping condition. We measured a maximum output power of 3.9 W at 1077 nm while the highest slope efficiency was 51.2%, in quasi-CW regime. In CW, at the same laser wavelength, the output power was 2.2 W with a corresponding slope efficiency of 35.1%. The explored range of tunability, 97 nm, is to the best of our knowledge one of the broadest and continuous intervals measured with Yb-doped materials. Mixed Lu-Y ceramic sesquioxides appear then as a promising laser material for broadly tunable laser sources and, in consequence, for the generation of ultrashort laser pulses.