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[Journal of the American Ceramic Society - 2026 - Xu - Transparent Er  Y La 2O3 Ceramics With High La3  Concentration for.pdf](https://mdr.nims.go.jp/filesets/20812673-68ff-4ea8-8a73-75c44028c3f6/download)

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[Zehao Xu](https://orcid.org/0009-0007-0336-3332), [Hiroaki Furuse](https://orcid.org/0000-0002-9008-1697), Shogo Miyoshi, Tohru S. Suzuki

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[Transparent Er:(Y,La)                    <sub>2</sub>                    O                    <sub>3</sub>                    Ceramics With High La                    <sup>3+</sup>                    Concentration for Mid‐Infrared Laser Applications](https://mdr.nims.go.jp/datasets/8169f376-2f5a-4544-b4bd-ebc397d98eba)

## Fulltext

Transparent Er:(Y,La)2O3 Ceramics With High La3+ Concentration for Mid‐Infrared Laser ApplicationsJournal of the American Ceramic Society RESEARCH ARTICLETransparent Er:(Y,La)2 O3 Ceramics With High La3 + Concentration for Mid-Infrared Laser Applications Zehao Xu1 , 2 Hiroaki Furuse1 Shogo Miyoshi1 Tohru S. Suzuki1 , 2 1 National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan 2 Graduate School of Advanced Science and Engineering, Waseda University, Shinjuku, Tokyo, Japan Correspondence: Hiroaki Furuse ( Furuse.Hiroaki@nims.go.jp) Received: 30 April 2026 Revised: 3 July 2026 Accepted: 8 July 2026 Keywords: co-precipitation | laser materials | mid-infrared | spark plasma sintering | transparent ceramics ABSTRACT Exploration of mid-infrared laser materials with broad emission spectra is crucial for the generation of ultrashort pulses, particularly in spectroscopic and material processing applications. The incorporation of La3 + ions into Er:Y2 O3 , a representative mid-infrared laser material, induces crystal lattice distortion and broadens its emission spectrum. However, the La3 + doping concentration is typically limited to approximately 10 at.% owing to the formation of secondary phases. In this study, transparent (Er0.05 Y0.95- x Lax )2 O3 mixed sesquioxide ceramics with high La3 + concentration of x = 0.2 was fabricated together with x = 0, 0.05, and 0.1 via co-precipitation and low-temperature spark plasma sintering (SPS) to investigate the effects of La3 + concentration on mid-infrared emission properties. Both the emission spectral width and luminescence lifetime at approximately 2700 nm increased with increasing La3 + concentration. For x = 0.2, the values were approximately 17 nm and 3.8 ms, respectively, compared to approximately 4 nm and 3.3 ms for x = 0. Although the x = 0.2 sample achieved an in-line transmittance above 80% at 2720 nm, it was still lower than those of samples with lower La3 + content. Microstructural analysis revealed that La3 + addition reduced the average grain size and formed residual pores, likely responsible for increased optical scattering. To eliminate the residual pores, post-hot isostatic pressing (HIP) treatment was conducted at various temperatures, which resulted in improved optical transmittance. We believe that optimizing processing conditions could further enhance optical quality at high La3 + concentrations, making it a promising candidate for mid-infrared laser applications. 1T  c  E  s  v  L  l  p  m  b            To©Jh Introduction he 2.7 µm laser emission of Er3 + ions (4 I11/2 →4 I13/2 transition)oincides with strong water and water vapor absorption, makingr3 + -doped laser gain media promising candidates for medicalurgery, spectroscopic, and materials processing [ 1–3 ]. Amongarious host materials, cubic sesquioxide groups, such as Y2 O3 ,u2 O3 , and Sc2 O3 , are particularly promising for mid-infraredaser emission owing to their high thermal conductivity, lowhonon energy, large Stark splitting, and excellent thermo-echanical properties [ 4, 5 ]. For ultrashort pulse lasers, broad-and gain media are highly desirable, as smooth and broadhis is an open access article under the terms of the Creative Commons Attribution Licenriginal work is properly cited. 2026 The Author(s). Journal of the American Ceramic Society published by Wiley Periodournal of the American Ceramic Society , 2026; 109:e71031 ttps://doi.org/10.1111/jace.71031emission bands are essential for achieving shorter pulse durations[ 6 ]. Mixed sesquioxides, such as (Lu,Sc)2 O3 and (Y,Sc)2 O3 , haveshown enhanced emission bandwidths and compositional spec-tral tuning due to intrinsic crystal field disorder arising from themismatch in cation radii among trivalent ions (Y3 + : 0.90 Å, Lu3 + :0.86 Å, Sc3 + : 0.75 Å) [ 7, 8 ]. While Er3 + -doped mixed sesquioxides exhibit broader emissionbands than single sesquioxide hosts, further spectral broadeningis desirable for ultrashort-pulse mid-infrared lasers [ 7–12 ]. Inthe (Y,La)2 O3 system, the substantial cation radius differencebetween Y3 + (0.90 Å) and La3 + (1.03 Å) [ 13, 14 ] is expected tose, which permits use, distribution and reproduction in any medium, provided the icals LLC on behalf of The American Ceramic Society. 1 of 11https://doi.org/10.1111/jace.71031https://orcid.org/0009-0007-0336-3332https://orcid.org/0000-0002-9008-1697mailto:Furuse.Hiroaki@nims.go.jphttp://creativecommons.org/licenses/by/4.0/https://doi.org/10.1111/jace.71031http://crossmark.crossref.org/dialog/?doi=10.1111%2Fjace.71031&domain=pdf&date_stamp=2026-07-21i  c  p  e  c  t  e  e  s  c  l  p  m  iS  e  f  f  o  b  cL  E  k  b  f  o  e  p  t  c  w  c  iS  t  t  p  p  s  h  t  e c  h  a  d  s  t  w  s  aI  d  t  (                                          2 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Cnduce stronger local lattice distortion and modifications of therystal-field environment, subsequently impacting the emissionroperties of Er3 + ions. Moreover, the relatively lower phononnergy of La2 O3 ( ∼ 400 cm− 1 ) [ 15, 16 ] compared to Y2 O3 (591m− 1 ), Lu2 O3 (612 cm− 1 ), and Sc2 O3 (672 cm− 1 ) [ 17 ] suggestshat (Y,La)2 O3 mixtures may achieve the relatively lower phononnergy, potentially reducing non-radiative relaxation and thennhancing laser efficiency. Nonetheless, the melting point ofesquioxides, which typically exceeds 2400◦C, poses a significanthallenge for single crystal synthesis and consequently impedesarge-scale commercial production [ 18, 19 ]. By contrast, ceramicrocessing can produce transparent bulk ceramics below theirelting points with more homogeneous doping of laser-activeons [ 4, 20 ]. un et al. demonstrated high transparency and strong lasermission at 2715 and 2727 nm from Er:(Y0.9 La0.1 )2 O3 ceramicsabricated by hot pressing at 1700◦C [ 21 ]. Balabanov et al. alsoabricated (Er0.07 Y0.83 La0.1 )2 O3 ceramics with a transmittancef 80% by vacuum sintering and observed additional spectralroadening in the mid-infrared absorption and emission bandsompared to Er:Y2 O3 ceramics [ 22 ]. a3 + doping effectively enhanced the emission capability ofr3 + ions in Er:Y2 O3 system. However, to the best of ournowledge, La3 + concentrations exceeding 10 at.% have rarelyeen reported in previous studies. This limitation likely arisesrom the formation of secondary phases such as monoclinicr perovskite phases, when solubility or temperature limits arexceeded in the Y2 O3 -La2 O3 solid solution system [ 23–27 ]. Suchhase formation is considered the primary obstacle to fabricatingransparent ceramics. Therefore, investigating fabrication pro-esses to achieve optical transparency in Er:(Y,La)2 O3 ceramicsith high La3 + content and examining the effect of elevated La3 +oncentrations on luminescence properties are of considerablenterest. park plasma sintering (SPS) is an advanced sintering techniquehat enables fabrication of dense ceramics with fine microstruc-ures at relatively lower sintering temperatures than conventionalressure-less vacuum sintering [ 28–32 ]. By employing SPS, trans-arent rare earth doped Y2 O3 ceramics with grain sizes aroundeveral 100 nm have been developed [ 33–36 ], and these materialsave been applied to laser materials and a saturable absorber inhe mid-infrared region [ 36 ]. This approach is also consideredffective for avoiding secondary phase formation in (Y,La)2 O3eramics that would otherwise occur during high-temperatureeat treatment. Additionally, co-precipitation has been reporteds an effective method for preparing fine powders with highoping concentrations and has the potential to overcome solidolubility limitations caused by diffusion constraints in tradi-ional solid-state reaction methods [ 37, 38 ]. Thus, combining SPSith co-precipitated powders provides an efficient strategy touppress secondary phase formation in (Y,La)2 O3 ceramics andchieve transparent ceramics for laser applications. n this study, we investigated the fabrication of transparent Er3 +oped (Y,La)2 O3 mixed sesquioxide ceramics with high La3 + con-ent via co-precipitation followed by SPS and hot isostatic pressingHIP) treatments. We systematically investigated the effects ofof 11reathigh La3 + content on the microstructure, optical properties, andemission behavior of these potential mid-infrared laser materials.2 Experimental Procedure 2.1 Material Preparation Figure 1 shows a schematic of the experimental procedure.High-purity yttrium nitrate hexahydrate, lanthanum nitrate hex-ahydrate, and erbium chloride hexahydrate were used as startingmaterials and dissolved in deionized water according to thestoichiometric ratio of (Er0.05 Y0.95- x Lax )2 O3 ( x = 0, 0.05, 0.1,0.2). Analytical-grade ammonium bicarbonate was used as theprecipitant and diluted with deionized water. The precipitantsolution was dripped into the mixed metal ion solution understirring. After precipitation, the solution was continuously stirredand aged for approximately 12 h. The precursor was collected bycentrifugation, washed several times with deionized water, anddried. Finally, the precursor was calcined at 1200◦C for 2 h in air.After sieving, the powder was subjected to SPS (LABOX-325,Sinter Land, Japan) under vacuum. The temperature was moni-tored using a pyrometer. The sintering temperature, heating rate,and holding time were 1300◦C, 5◦C/min, and 1 h, respectively.An applied pressure of 80 MPa was preloaded and maintainedconstantly until completion of the sintering process. After SPS,the sintered ceramics were annealed in air, and both surfaceswere polished for characterization. Three sets of HIP treatmentsfor SPSed samples were conducted using a HIP furnace (O2 -Dr.HIP, Kobe Steel, Japan) under Ar pressure of 180 MPa at 1200◦C,1300◦C, and 1400◦C for 2 h, respectively. 2.2 Characterization For material characterization, the phase compositions of thepowders and sintered ceramics were measured using an X-raydiffractometer (Ultima IV, Rigaku Co., Japan). To evaluate thephonon energies of the host materials, Raman shift spectra wererecorded using a Raman microscope (inVia Reflex, Renishaw Co.,UK) with a 785 nm laser for undoped Y2 O3 and (Y0.8 La0.2 )2 O3 calcinated powders to avoid absorption owing to Er3 + ions. The in-line optical transmittance of the ceramics was measured using aUV-VIS-NIR spectrometer (UV-3600i Plus, Shimadzu Co., Japan).The morphologies of the powders and the microstructures of thesintered ceramics were observed using a field-emission scanningelectron microscope (S-4800, Hitachi Co., Japan). To examine themicrostructure of the sintered ceramics, the polished surfaceswere thermally etched at 900◦C for 1 h. 2.3 Luminescence Properties The luminescence spectra and decay curves were obtained usinga 976 nm laser diode as the excitation source. Mid-infraredluminescence spectra and temporal decay curves were measuredusing an optical spectrum analyzer (OSA205C, Thorlabs Co.,USA) and an InAsSb detector, respectively. Journal of the American Ceramic Society, 2026ive Commons LicenseFIGURE 1 Experimental procedure for fabricating (Er0.05 Y0.95- x Lax )2 O3 transparent ceramics. FIGURE 2 FE-SEM images of the as-calcined powder for various La3 + concentrations: (a) x = 0, (b) x = 0.05, (c) x = 0.1, and (d) x = 0.2. 3F  d  a  p  t  T  w  f           J 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applica Results and Discussion igure 2 shows FE-SEM micrographs of calcined powders withifferent La3 + doping concentrations. All the samples exhibited loosely aggregated morphology composed of submicron-sizedarticles. The particles displayed irregular polyhedral shapes,ypical of nanoscale powders produced via wet chemical methods.here was no evident change in morphology or powder dispersionith respect to La3 + concentration; all the powders remained uni-ormly dispersed with particle diameters of approximately 80 nm.ournal of the American Ceramic Society, 2026Figures 3 and 4 show the x-ray diffraction (XRD) patterns of thecalcined powders and the sintered ceramics after SPS, respec-tively. All the diffraction peaks of both the powders and ceramicsmatched well with the Y2 O3 phase (No. 86–1326) [ 39 ], indicatingthat the powders and ceramics have a cubic structure withoutany secondary phases. The XRD peak positions shifted slightlywith increasing La3 + content owing to changes in the latticeconstant. Additionally, the full width at half maximum (FWHM)of the characteristic peak of the powder with 20 at.% La3 + showed significant broadening, as Figure 3b shows, reflecting3 of 11ble Creative Commons LicenseFIGURE 3 (a) X-ray diffraction patterns of the calcined (Er0.05 Y0.95- x Lax )2 O3 powder for various La3 + concentrations; (b) magnified image of (222) peak. FIGURE 4 (a) X-ray diffraction patterns of the as-sintered (Er0.05 Y0.95- x Lax )2 O3 ceramics for various La3 + concentrations; (b) magnified image of (222) peak. i  bU  p       4 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativnternal lattice disorder that may contribute to increased emissionandwidth [ 39 ]. sing the Miller index (ℎ𝑘𝑙 ) model and Bragg’s law, the latticearameter ( 𝑎) of the cubic crystal can be calculated as follows: 𝑑ℎ𝑘𝑙 =𝑎 √ℎ2 + 𝑘2 + 𝑙2 (1)of 112 𝑑ℎ𝑘𝑙 sin 𝜃 = 𝜆 (2)where 𝑑ℎ𝑘𝑙 is the interplanar spacing, 𝜃 is the diffraction angle,𝜆 is the X-ray wavelength, and (ℎ𝑘𝑙 ) are the Miller indices of thediffraction plane. The lattice parameters of powders and ceramicsare plotted as a function of La3 + content in Figure 5 , revealinga linear increase with La3 + concentration, signifying successfulJournal of the American Ceramic Society, 2026e Commons LicenseFIGURE 5 Lattice constants as a function of the La3 + concentration for (Er0.05 Y0.95- x Lax )2 O3. FIGURE 6 Raman spectra of the undoped Y2 O3 and (Y0.8 La0.2 )2 O3 powders. i  oR  a  w  s  T p  L  mF  s  n  f  t                                                J 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatincorporation of La3 + ions into the Y2 O3 lattice and the formationf a single-phase solid solution. aman spectra of the calcined Y2 O3 and (Y0.8 La0.2 )2 O3 powdersre shown in Figure 6 . The spectra of both samples matchedell with the typical nature of cubic sesquioxides, but thepectrum of (Y0.8 La0.2 )2 O3 broadened and was slightly red shifted.he maximum phonon energies of the Y2 O3 and (Y0.8 La0.2 )2 O3owders were 593 and 579 cm− 1 , indicating that incorporation ofa3 + ions likely reduces non-radiative relaxation in the ceramicaterials. igure 7a,b shows the sample images and in-line transmittancepectra of the (Er0.05 Y0.95- x Lax )2 O3 ceramics after SPS with a thick-ess of 1.2 mm. The in-line transmittance ( T ) can be expressed as aunction of sample thickness and internal scattering and absorp-ion losses, namely, 𝑇 = 𝑇0 exp [− (𝛼 + 𝜎) 𝑑 ] , where 𝛼 denotes theournal of the American Ceramic Society, 2026absorption coefficient, 𝜎 denotes the scattering coefficient, and 𝑑denotes the sample thickness. The theoretical transmittance ( T0 )can be obtained from the Fresnel reflectance ( R ) as follows: 𝑇0 = ( 1 − 𝑅 ) 2 (3)𝑅 = ( 1 − 𝑛 ) 2 ( 1 + 𝑛 ) 2 (4)where 𝑛 denotes the refractive index dispersion of the undopedY2 O3 material [ 22, 40 ]. The in-line transmittance of the Er:Y2 O3 ( x = 0) ceramic was82.1% at 2720 nm, which is comparable to the theoretical value of82.6%. This corresponds to a loss coefficient of 0.05 cm− 1 , which iscloser to the laser quality requirements. The transmittance of theother three ceramics showed a decreasing trend with increasingLa3 + content, and the ceramic with x = 0.2 exhibited a minimumtransmittance of 80.8% with a corresponding loss coefficient of0.18 cm− 1 . Moreover, the transmittance of the ceramics decreasedmore significantly with La3 + content in the wavelength rangebelow 1500 nm, notably at the excitation wavelength of 976 nm,mainly owing to residual pores within the ceramics. The microstructural images of the polished ceramic surfaces areshown in Figure 8 . No secondary phases were observed for anyLa3 + content, which corresponded to the XRD results shown inFigure 4 . In Figure 8a , the sintered ceramic with 0 at.% La3 +concentration consists of extremely fine crystal grains. However,as shown in Figure 8b–d , the number of residual pores increasedwith increasing La3 + concentration. The average grain size ofthe ceramics decreased from 298 nm for Er:Y2 O3 ceramic to 247,187, and 131 nm for those containing 5, 10, and 20 at.% La3 +concentrations, respectively. This indicates that the decrease inaverage grain size may be attributed to La3 + ion acting as asintering inhibitor [ 25, 41 ], leading to suppressed grain growthand an increased number of residual pores. One approach tofurther improve optical transmittance is to optimize the SPSsintering conditions, such as sintering temperature or appliedpressure. The SPSed samples were subjected to subsequent HIP processingat different temperatures to improve optical quality by removingresidual pores. Figure 9 presents in-line transmittance spectra andcorresponding photographs of the (Er0.05 Y0.95- x Lax )2 O3 ceramicsafter different HIP treatments. Compared with SPSed ceramics,post-HIP ceramics exhibited improved optical transparency. Inthe visible to near-infrared range, the in-line transmittancegenerally increased with increasing HIP temperature for x = 0,0.05, and 0.1, attributed to the effective removal of residual pores.By contrast, the optical transmittance of the sample with x = 0.2improved after HIP processing at 1200◦C, while further increasesin HIP temperature led to reduced optical transmittance. Notably,the transmittance of the sample treated by HIP at 1400◦Cdecreased dramatically and became almost opaque. Figure 10 illustrates the phase composition of x = 0.2 samples aftervarying HIP treatments. In Figure 10a , the SPSed sample treatedat 1200◦C remained a single cubic phase. However, increasingthe HIP temperature introduced several new diffraction peaks5 of 11ve Commons LicenseFIGURE 7 (a) Sample images and (b) in-line transmittance spectra of the (Er0.05 Y0.95- x Lax )2 O3 ceramics for various La3 + concentrations after SPS. FIGURE 8 FE-SEM images of the polished (Er0.05 Y0.95- x Lax )2 O3 ceramic surfaces for various La3 + concentrations: (a) x = 0, (b) x = 0.05, (c) x = 0.1, and (d) x = 0.2. 6 of 11 Journal of the American Ceramic Society, 2026 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseFIGURE 9 In-line transmittance spectra of the (Er0.05 Y0.95- x Lax )2 O3 ceramics with corresponding photographs after different HIP treatments for various La3 + concentrations: (a) x = 0, (b) x = 0.05, (c) x = 0.1, and (d) x = 0.2. i  p  m7 p  p  m  i  cT  f  a  f  o  s  b  i  4  e  a  s  t  c  S  a               J 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatin the XRD patterns. As shown in Figure 10b , these diffractioneaks were located at intermediate position between those ofonoclinic Y2 O3 phase (No. 90–4438) and La2 O3 phase (No. 76–413), suggesting the possible formation of a monoclinic (Y,La)2 O3hase during high-temperature HIP treatment. This secondaryhase acts as a scattering center, leading to reduced optical trans-ittance. These results suggest that low-temperature sinterings essential for fabricating transparent ceramics with high La3 +oncentrations. he measured luminescence spectra in the mid-infrared rangeor the SPSed (Er0.05 Y0.95- x Lax )2 O3 ceramics before HIP treatmentre shown in Figure 11a . The broad luminescence spectra spanrom 2580 to 3000 nm, corresponding to the 4 I11/2 →4 I13/2 transitionf Er3 + ions. With increasing La3 + content, the luminescencepectra became less structured and exhibited inhomogeneousroadening. Generally, two possible lasing modes were observedn the mid-infrared spectral region at 2710 nm and 2850 nm [ 22,2 ]. For the most intense peak centered at around 2720 nm, themission bandwidth (FWHM) of the sample with x = 0.2 reachedpproximately 17 nm compared with approximately 4 nm for theample with x = 0. The incorporation of larger La3 + ions intohe Y2 O3 lattice induces local lattice distortion and modifies therystal-field environment around the Er3 + ions. Consequently, thetark splitting of the 4 I11/2 manifolds at 2720 nm may vary slightlymong different Er3 + centers. The overlap of emissions resultingournal of the American Ceramic Society, 2026from these local crystal-field perturbations leads to enhancedinhomogeneous broadening of the mid-infrared luminescenceband. For another intense peak band in the range of 2820–2880 nm shown in Figure 11b , the FWHM of the Er:(Y0.8 La0.2 )2 O3 ceramics broadened to approximately 18 nm. These results con-firm that high La3 + incorporation effectively enhances spectralbroadening of the mid-infrared emission, which is advantageousfor developing ultrashort pulse lasers. The luminescence decay curves from the 4 I11/2 →4 I13/2 transitionof Er3 + in the different samples are shown in Figure 12 . Thesewere fitted using the following function to evaluate the averagelifetime: 𝐼 ( 𝑡) = 𝐴1 exp ( − 𝑡 𝜏1 ) + 𝐴2 exp ( − 𝑡 𝜏2 ) (5)𝜏ave =𝐴1 ( 𝜏1 ) 2 + 𝐴2 ( 𝜏2 ) 2 𝐴1 𝜏1 + 𝐴2 𝜏2 (6)where 𝐴1 + 𝐴2 ≈ 1 and 𝜏ave denotes the average luminescencelifetime. The average luminescence lifetimes were 3.3, 3.4, 3.6, and 3.8 msfor ceramics with x = 0, 0.05, 0.1, and 0.2, respectively. Interest-7 of 11ve Commons LicenseFIGURE 10 (a) XRD patterns for the (Er0.05 Y0.75 La0.2 )2 O3 samples after HIP treatment at 1200◦C, 1300◦C, and 1400◦C, respectively. (b) Magnified image of the XRD patterns for the sample treated at 1400◦C. FIGURE 11 Luminescence spectra of the (Er0.05 Y0.95- x Lax )2 O3 ceramics for various La3 + concentrations: (a) full spectra; (b) a close look at the 2800–2880 nm wavelength range. 8 of 11 Journal of the American Ceramic Society, 2026 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseFIGURE 12 Mid-infrared luminescence decay curves of the (Er0.05 Y0.95- x Lax )2 O3 ceramics for various La3 + concentrations. i  W  c  q  t  l  1  t  c  c  H  h  f  t  W  r  e4T  i  (  0  p  L  c  c  c  o  e  w  i  2  f  i  a  e  r                    J 15512916, 2026, 7, Downloaded from https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.71031 by National Institute For, Wiley Online Library on [21/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatngly, the average lifetime increased with increasing La3 + content.e attribute this to the reduction in maximum phonon energy oferamics, which suppresses multi-phonon relaxation and conse-uently enhances radiative efficiency at this wavelength. Notably,he (Er0.05 Y0.75 La0.2 )2 O3 ceramics exhibited a long luminescenceifetime of 3.8 ms and a broad emission bandwidth exceeding7 nm, signifying higher luminescence emission capability thanhe other samples. These results suggest that increasing the La3 +oncentration to 20 at.% can enhance the potential of theseeramics for ultrashort pulse mid-infrared laser applications.owever, achieving the suppression of secondary phases atigher La3 + concentrations requires careful optimization of theabrication process, including suitable powder synthesis, low-emperature SPS processing, and subsequent HIP treatment.e believe that further improvements in transmittance can beealized by optimizing these conditions, ultimately facilitatingfficient laser operation.  Conclusions he combination of the co-precipitation method and SPSs an effective strategy for fabricating highly transparentEr0.05 Y0.95- x Lax )2 O3 ceramics with x values of 0, 0.05, 0.1, and.2. SPS is currently the only practical method available forroducing transparent ceramics with high La3 + concentrations.a3 + ions were incorporated into the Y2 O3 lattice during theo-precipitation process, resulting in intrinsic disorder of therystal field and a decrease in maximum phonon energy, whichontributed to broadening of the emission spectra and extensionf the luminescence lifetime. For the sample with x = 0.2, themission spectral width at 2720 nm broadened to around 17 nm,hile the luminescence lifetime of the 4 I11/2 →4 I13/2 transitionncreased to 3.8 ms. However, the in-line transmittance at720 nm for the x = 0.2 sample decreased to 80.8% owing toormation of residual pores. Ultimately, further improvementn optical transmittance at the pump source wavelength waschieved by appropriate HIP treatment, which is significant forxploring more efficient ultrashort lasers in the mid-infraredegion. ournal of the American Ceramic Society, 2026Acknowledgments This study was supported by the JST FOREST Program (JPMJFR203S). Conflicts of Interest The authors declare no conflicts of interest. Data Availability Statement The data that support the findings of this study are available from thecorresponding author upon reasonable request. References 1 . J. S. Liu, J. J. Liu, and Y. Tang, “Performance of a Diode End-PumpedCr, Er: YSGG Laser at 2.79 µm,” Laser Physics 18, no. 10 (2008): 1124–1127,https://doi.org/10.1134/S1054660X08100022 . 2 . Z. D. Fleischman and T. Sanamyan, “Spectroscopic Analysis ofEr3 + :Y2 O3 Relevant to 2.7 µm Mid-IR Laser,” Optical Materials Express6, no. 10 (2016): 3109–3118, https://doi.org/10.1364/ome.6.003109 . 3 . C. Kränkel, A. Uvarova, C. 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See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttps://doi.org/10.1109/JSTQE.2014.2346618https://doi.org/10.1143/JJAP.7.404https://doi.org/10.1016/j.jeurceramsoc.2014.07.016https://doi.org/10.1016/j.optmat.2023.113542 Transparent Er:(Y,La)2O3 Ceramics With High La3+ Concentration for Mid-Infrared Laser Applications 1 | Introduction 2 | Experimental Procedure 2.1 | Material Preparation 2.2 | Characterization 2.3 | Luminescence Properties 3 | Results and Discussion 4 | Conclusions Acknowledgments Conflicts of Interest Data Availability Statement References