Simple route to NdYAG transparent ceramics

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Cite this: J. Mater. Chem. C, 2015, 3, 861
However, these oligouorene functionalized oligomers may suﬀer from the unwanted long wavelength emission under long-term device operation, similar to polyuorene-based macromolecules.34–36
Received 26th September 2014 Accepted 17th November 2014 DOI: 10.1039/c4tc02173h /MaterialsC
Starburst 4,40,400-tris(carbazol-9-yl)triphenylamine-based deep-blue ﬂuorescent emitters with tunable oligophenyl length for solution-processed undoped organic lightemitting diodes†
Introduction
Since 1987, organic light-emitting diodes (OLEDs) have attracted tremendous attention due to their potential applications in at-panel displays and solid-state lightings.1–10 To achieve fullcolor displays, three primary RGB luminescent materials with excellent stability, eﬃciency and color purity are required. With respect to green and red counterparts, it seems to be a big challenge to develop blue emitters, especially deep-blue ones that have a Commission Internationale de l'Eclairage (CIE) y coordinate value of <0.10, because the intrinsic wide bandgap would inevitably result in ineﬃcient charge injection to an emitting layer (EML).11 Therefore, great eﬀorts should be paid to the design of deep-blue emitters to push forward the commercialization of full-color OLEDs.

日立金属公司奈米晶软磁合金材料

For safety and the proper usage, you are requested to approve our product specifications or to transact the approval sheet for product specifications before ordering.This catalog and its contents are subject to change without notice.Saturation flux density B s (T)1031041051060.50.0 1.0 1.5 2.02.5R e l a t i v e p e r m e a b i l i t y µrThe limit of the conventional special material21) Satisfy both high saturation magnetic flux density and high permeabilityHigh saturation magnetic flux density comparable toFe -based amorphous metal. High permeability com-parable to Co-based amorphous metal.2) Low core loss1/5th the core loss of Fe based amorphous metal andapproximately the same core loss as Co-based amor-phous metal.3) Low magnetostrictionLess affected by mechanical stress. Very low audio noise emission.4) Excellent temperature characteristics and small aging effectsS mall permeability variation (less than ±10%) at atemperature range of -50°C~150°C. Unlike Co-based amorphous metals, aging effects are very small.5) Excellent high frequency characteristicsHigh permeability and low core loss over wide fre-quency range, which is equivalent to Co-based amor-phous metal.6) Flexibility to control magnetic properties“B-H curve shape”during annealingThree types of B-H curve squareness, high, middleand low remanence ratio, corresponding to various applications.Fe based amorphousCo based amorphousPermalloyf=1 kHzSi-steelExamples of DC B-H curveRelationship between relative permeability andsaturation flux density of various soft magnetic materialsHB(T)M Type(FT-3M)H max =800 A/mH max =8 A/m1.0HB(T)L Type(FT-3L)H max =800 A/m H max =8 A/m1.0B(T)HH max =800 A/m H max =8 A/m1.0H Type(FT-3H)Fe-Al-SiMn-Zn ferriteWhat is FINEMET ® ?FINEMET®Nanocrystalline Fe-based Soft Magnetic Material with High Saturation Flux Density and Low Core LossFINEMET ® is the product ofThe best solution for energy saving, electromagnetic noise reduction and size reduction.Superior to Conventional MaterialFeaturesB-H Curve Control for FINEMET ®FINEMET ® core ’s magnetic properties, “B-H curve ” can be controlled by applying a magnetic field during anneal-ing. There are three types of B-H curves. 1) H type: a magnetic field is applied in a circumferential direction during annealing. 2) M type: no magnetic field is applied during annealing. 3) L type: a magnetic field is applied vertically to the core plane during annealing.H, M or L implies B-H squarenessThe precursor of FINEMET ® is amorphous ribbon (non-crystalline) obtained by rapid quenching at one million °C/second from the molten metal con-sisting of Fe, S i, B and small amounts of Cu and Nb. These crystallized alloys have grains which are extremely uniform and small, “about ten nanome-ters in size ”. Amorphous metals which contain cer-tain alloy elements show superior soft magneticproperties through crystallization. It was commonly known that the characteristics of soft magnetic ma-terials are “larger crystal grains yield better soft magnetic properties ”. Contrary to this common be-lief, soft magnetic material consisting of a small, “nano-order ”, crystal grains have excellent soft magnetic properties.FINEMET ®For safety and the proper usage, you are requested to approve our product specifications or to transact the approval sheet for product specifications before ordering.This catalog and its contents are subject to change without notice.Hitachi Metals Ltd. produces various types of soft magnetic materials, such as Permalloy, soft ferrite, amorphous metal, and FINEMET ®, and we use these materials in our product’s applications. We continually improve our material technology and develop new applications by taking advantage of the unique characteristics these materials provide. FINEMET ® is a good example. It is our hope, FINEMET ® will be the best solution for your application.3Excellent temperature characteristicsHigh permeability High squarenessLow core lossHigh saturation flux densityLow magnetstrictionEnergy saving Volume reduction High performance Noise reduction High frequency useEMI filtersCommon mode chokes Magnetic shielding sheets Electromagnetic wave absorbersCurrent sensors Magnetic sensorsMagnetic amplifier Pulsed power cores Surge absorbersHigh voltage pulse transformers High frequency power transformersActive filters Smoothing choke coils Accelerator cavityRapid quenchingNano structurecontrolAnnealing MeasurementElectromagnetic circuit designing Electromagnetic and electro circuit designingAdvantages of FINEMET ®Picture of FINEMET ® through a transmission electron microscopeFeatures of FINEMET ®TechnologyFeatures and typical applications of FINEMET ®For safety and the proper usage, you are requested to approve our product specifications or to transact the approval sheet for product specifications before ordering.This catalog and its contents are subject to change without notice.41.231.200.500.482.52.73,5007.3X10Common Mode Chokes for *EMI filtersSaturation flux density B s (T)Squareness ratio B r /B s Coercive force H c (A/m)Pulse permeability µrp Core loss P cv (J/m 3)Curie temperature T c (ºC)Saturation magnetostriction Electrical resisitivity (µΩ•m)Density d (kg/m 3)*: DC magnetic properties at 800A/m **: Pulse width 0.1 µs, operating magnetic flux density B=0.2TFT-3MMaterialCo-based amorphous0.600.530.800.780.300.294,5007.7X10Ni-Zn ferrite0.380.290.710.6030205005.2X10*EMI: Electro Magnetic InterferenceVolume reduction with high permeabilityHigh voltage surge suppression with high saturation flux densityMajor Application of FINEMET®FINEMET ® has higher impedance permeabili-ty (µrz ) and much smaller temperature de-pendence of permeability over a wider fre-quency range than Mn-Zn ferrite.Consequently, the volume of FINEMET ® core can be reduced to 1/2 the size of a Mn-Zn fer-rite core while maintaining the same perfor-mance at operating temperature of 0°C~100°C. Also, it has approximately three times higher saturation flux density than Mn-Zn ferrite and as a result it is hardly saturated by pulse noise.FINEMET ® Beads are made of FINEM ET ® FT -3M material. As below table describes, the saturation magnetic flux density is twice as high as that of Co-based amorphous metal and Ni-Zn ferrite, and the pulse permeability and the core loss are comparable to Co-based amorphous metal. Because of the high curie temperature (570ºC), FINEM high temperature. These cores are suitable for suppression of reverse recovery current from the diode and ringing or surge current from switching circuit.Comparison of magnetic and physical properties among FT-3M and conventional materialsFINEMET ® BeadsThe followings are examples of FINEMET ® application by taking advantage of high20ºC 100ºC 20ºC 100ºC 20ºC 100ºC*******10410510101102103104Frequency(kHz)102p e r m e a b i l i t y µr z140ºC 100ºC -40CFINEMETFor safety and the proper usage, you are requested to approve our product specifications or to transact the approval sheet for product specifications before ordering.This catalog and its contents are subject to change without notice.510-310-210-110010110-210-1100Flux density B m (T)C o r e l o s s P c m (W /k g )=0.05mm)6.5% Si-Steel(t=0.05mm)(FT-3M)The core loss of FINEMET ® (FT -3M) cut core has less than 1/5th the core loss of Fe based amorphous metal and Mn-Zn ferrite, and less than 1/10th the core loss of silicon steel at 10k Hz, Bm=0.2T. FINEMET ® has significant-ly lower core loss and thus makes it possible to reduce the size of the core for high fre-quency power transformer. Also, the magne-tostriction of FT -3M is 10-7order and, as a re-sult, cores made from this material will make very little audible noise when compared to cut cores made from Fe based amorphous metal and silicon steel.High Frequency Power TransformerComparison of core materials applied in saturable cores for magnetic pulse compression circuitPulsed Power CoresPET film 2.04 1680 ~– 1.3 40 0.74 1.75PET film 0.78 180 ~– 1 –0.65 70 ~– 3 ~– 1 8 1 1Size reduction with low core lossSize reduction and lower core lossFINEMET ® pulsed power cores use a thin ceramic insulation which has a high break down voltage. FINEMET ® pulsed power cores are suitable for saturable cores and step-up pulse transformer cores that are used in high voltage pulsed power supplies for Excimer lasers and accelerators, and for cavity cores used in induction linacs and RF accelerators.InsulationEffective induction swing K Half-cycle core loss Pc (J/m Relative permeability at saturation range µr (sat )Reset magnetizing force H (reset ) (A/m)Volume ratio of saturable cores Total core loss ratio of saturable coresCore materialFe-basedamorphous metalCo-basedamorphous metalNi-Zn ferriteFINEMET ®FT-3H Pulse duration compression ratio: 5.0 (input pulse duration 0.5µs, output pulse duration0.1µs)K: Packing factor B m : Maximum operation flux densityFor safety and the proper usage, you are requested to approve our product specifications or to transact the approval sheet for product specifications before ordering.This catalog and its contents are subject to change without notice.6Manufacturing Process and Microstructure of FINEMET ®Cu-rich area (Cu cluster)Amorphousfcc Cu bcc Fe-(Si)Remaining amorphous phase (Nb, B-rich area)CrystallizationFINEMET ® after proper annealingThickness: ~18 µmgrain size: ~10nmRapidly quenched amorphous phase Amorphous metal ribbonRibbon winding (Configuration)Nanocrystallizationtfcc Cu bcc Fe-(Si)Amorphous phase (Nb, B-rich area)(High T x )AmorphousManufacturing Process of FINEMET ®Crystallization Process of FINEMET ®Overview of manufacturing process, crystallization process and annealing conditionsAmorphous metal as a starting point, Amorphous Cu-rich area the nucleation of bcc Fe from Cu bcc Fe(-Si) shows the crystallization process. At the final stage of this crystallization process, the grain growth is suppressed by the stabilized remaining amorphous phase at the grain boundaries. This stabilization occurs because the crystallization temperature of the remainingamorphous phase rises and it becomes more stable through the enrichment of Nb and B. Synergistic ef-fects of Cu ad d ition, “which causes the nucleation of bcc Fe ” and Nb addition, “which suppresses the grain growth ” creates a uniform and very fine nanocrystalline microstructure.A below diagram shows the process for the creation of amorphous ribbon for FINEMET ® and a typical FI-NEME T ® core. The amorphous ribbon is the precursor material of FINEME T ®. This ribbon, “which is about 18 µm in thickness ”, is cast by rapid quenching, called“single roll method ”, then the amorphous ribbon is wound into a toroidal core. Finally, the heat treatment is applied to the core for crystallization in ord er to obtain excellent soft magnetic properties of FINEME T ®.CoreFINEMET ® coreApply rapid quenching to high temperature melt con-sists of Fe, as a main phase, Si, B, Cu and Nb.The early stage ofannealingThe early stage of crystallizationCastingRapidquenchingSingle roll methodAnnealingFor safety and the proper usage, you are requested to approve our product specifications or to transact the approval sheet for product specifications before ordering.This catalog and its contents are subject to change without notice.720nmExample of annealing for M typeAnnealing Conditions500~570°CAir cooling or furnance cooling1~2h0.5~3hHeat treatment in inert gas atmosphere (N 2 or Ar)TimeRoomtemperatureT e m p e r a t u r e100~200°CThe diagram shows the typical annealing conditions for M type.This process requires proper heat treatment conditions according to the desired magnetic properties.Microstructure of FINEMET ®A below picture shows the microstructure of FINEMET ® through a transmission electron microscope.FINEMET ® consists of ultra fine crystal grains of 10nm order. Main phase is bcc Fe(-Si) and remaining amorphous phase around the crystal grains.Microstructure of FINEMET ®FINEMETbrochure No. HL-FM10-CPrinted in April 2005(T-FT 3)Soft Magnetic Materials Company Head Office 2-1 Shibaura 1-chome, Seavans North Bldg.Minato-ku, Tokyo 105-8614, JapanTel:+81-3-5765-4041 Fax: +81-3-5765-8313Kansai Sales Office5-29 Kitahama 3-chome, Nissei Yodoyabashi buildingChuo-ku, Osaka 541-0041, JapanTel:+81-6-6203-9751 Fax:+81-6-6222-3414Chubu-Tokai Sales Office13-19 Nishiki 2-chome, Takisada building, Naka-kuNagoya-shi, Aichi, 460-0003, JapanTel:+81-52-220-7470 FAX:+81-52-220-7486Room 1107, 10F., West WingTsim Sha Tsui Centre66 Mody Road, Tsimshatsui EastKowloon, Hong KongTel:+852-2722-7680 Fax:+852-2722-7660Hong KongSouth-East Asia12 Gul Avenue, Singapore 629656Tel:+65-6861-7711 Fax:+65-6861-9554North America440 Allied Drive Conway, SC 29526, U.S.A.Tel:+1-843-349-7319 Fax:+1-843-349-6815NOTICE OF DISCLAIMEREuropeImmermannstrasse 14-16, 40210 Dusseldorf, Germany Tel:+49-211-16009-18 Fax:+49-211-16009-60Information in this brochure does not grant patent right, copyright or intellectual property rights of Hitachi Metals or that of third parties. Hitachi Metals disclaims all liability arising out using information in this brochure for any case of patent right, copyright or intellectual property rights of third parties.Do not duplicate in part or in its entirety this brochure without written permission from Hitachi Metals Ltd.This brochure and its contents are subject to change without notice; specific technical charac-teristics are subject to consultation and agreement.Please inquire about our handling manual for specific applications of FINEMET ®, these man-uals detail the exact guaranteed characteristics of FINEMET ® for a specific application.Above contact addresses are as of April 2005. The addresses are subject to change without notice.If you find difficulty contacting Hitachi Metals, please contact below: Hitachi Metals Ltd. Corporate Communication Group .Tel : +81-3-5765-4076 Fax : +81-3-5765-8312 E-mail : hmcc@hitachi-metals.co.jp••。

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Zhang_et_al-2013-Journal_of_the_American_Ceramic_Society

Enhanced 2.0l m Emission and Lowered Upconversion Emission in Fluorogermanate Glass-Ceramic Containing LaF 3:Ho 3+/Yb 3+byCodoping Ce 3+IonsJia-Peng Zhang,Wei-Juan Zhang,Jian Yuan,Qi Qian,and Qin-Yuan Zhang †State Key Laboratory of Luminescence Materials and Devices,Institute of Optical Communication Materials,South ChinaUniversity of Technology,Guangzhou 510641,China Intense 2.0l m emission of Ho 3+has been achieved through Yb 3+sensitization in ﬂuorogermanate glass-ceramic (GC)con-taining LaF 3pumped with 980nm laser diode (LD).The observation of concurrent emissions at 538,650,and 1192nm points to the additional deexcitation routes based on infrared-to-visible upconversion processes and Ho 3+:5I 6?5I 8radiative parative investigations of photoluminescent spectra and decay curves have indicated the eﬀective role of Ce 3+ions in enhancing the 2.0l m ﬂuorescence along with suppressing the occurrence of these concurrent emissions.This would oﬀer a promising approach to develop compact and eﬃ-cient 2.0-l m laser systems.I.IntroductionRECENTLY ,ﬁber lasers operating at ~2.0l m have beenthe subjects of intense research,due to their potential applications in the ﬁeld of military,laser medical surgery,and atmospheric pollution monitoring.1–3In this respect,tri-valent rare-earth (RE)ions,Tm 3+,and Ho 3+are commonly doped as activators for their corresponding radiative transi-tions,i.e.,Tm 3+:3F 4?3H 6and Ho 3+:5I 7?5I 8lying in the neighborhood of 2.0l m.4,5Compared with Tm 3+ions,Ho 3+ions are characteristics of a broad emission band,large stimulated emission cross section,and long-lived laser upper level.6However,Ho 3+ions cannot be directly excited by commercially available high-power AlGaAs (800nm)or InGaAs (980nm)LD,due to the absence of well-matched absorption bands.To solve this problem,Tm 3+,Yb 3+,Er 3+,and Bi ions are generally codoped as promising sensi-tizers,which could initially absorb the excitation energy and further transfer it to Ho 3+ions.7–10Yb 3+ion is known as an eﬃcient sensitizer for its broad absorption band exactly lying in the emission range of InGaAs LD.Furthermore,the simple energy level diagram with only one excited state (2F 5/2)lying at about 10000cmÀ1above the ground state (2F 7/2)would reduce the incidence of multiphonon relaxation,excited-state absorption,and direct Yb 3+–Ho 3+back transfer.11So far,oxyﬂuoride glass-ceramic (GC)has been considered as a prospective host matrix for RE ions not only for the low phonon energy environment provided by ﬂuoride nanocrystals but also for the high chemical and mechanical stabilities remained in oxide glass.12,13Based on this fact,RE-doped transparent oxyﬂuoride GC ﬁnd potential applica-tions in numerous photonic devices such as upconversionlasers,color display,sensors,and optical data storage.14It is well accepted that the low phonon energy environment can promote luminescence eﬃciency by reducing nonradiatively relaxation rates.Hence,the probability of upconversion in Yb 3+/Ho 3+couple can be enhanced at the same time,which may compete with 2.0-l m radiative transition.With two manifolds separated by the energy gap of about 2000cm À1,15Ce 3+ion is generally used as an eﬀective deactivator dopant to improve the performance of Er 3+ 1.5l m emission by reducing the upconversion emission.16Basically,there exists an phonon-assisted energy-transfer process of 4I 11/2(Er 3+)+2F 5/2(Ce 3+)?4I 13/2(Er 3+)+2F 7/2(Ce 3+),which favors the population accumulation of Er 3+1.5l m emission level 4I 13/2.To some extent,the energy level diagram for Ho 3+is akin to that of Er 3+only with diﬀerent energy gap between adjacent levels.In view of the comparably small energy mismatch between Ho 3+:5I 6–5I 7(~3400cm À1)and Ce 3+:2F 7/2–2F 5/2(~2000cm À1)energy gaps,the possibility of adding Ce 3+as an energy acceptor has been further explored by Tian et al.17and Tao et al.18It is conﬁrmed that the incorporation of Ce 3+not only facilitate Yb 3+?Ho 3+energy transfer but also enhance the Ho 3+2.0l m emission in ﬂuorophosphate glass and tellurite glass,respectively.17,18In this article,Ho 3+/Yb 3+and Ho 3+/Yb 3+/Ce 3+cod-oped ﬂuorogermanate glass and GC containing LaF 3nano-crystals have been prepared.Eﬀects of Ce 3+codoping on the spectral properties of Ho 3+/Yb 3+-codoped GC have been investigated and the possible energy-transfer mechanisms involved have been systematically analyzed and discussed.II.Experimental ProcedureThe oxyﬂuoride precursor glasses (denoted as PG x ,x =0,0.25,0.5, 1.0,and 2.0)were prepared according to the nominal molar composition of 50GeO 2–20Al 2O 3–15LaF 3–15LiF –0.25Ho 2O 3–2Yb 2O 3–x CeF 3.The starting materials are high-purity (99.99%)GeO 2,LaF 3,Ho 2O 3,Yb 2O 3,CeF 3,and analytical reagent-grade Al 2O 3and LiF.Accurately weighed batches of 15g raw materials were mixed and then melted in covered corundum crucibles at 1350°C for 1h in ambient atmosphere.The melts were then quenched on a preheated stainless steel plate and annealed at 520°C for 2h to remove residual stress.To obtain transparent GC,the precursor glass samples were cut into several pieces of the same size and sub-jected to thermal treatment at 570°C for 4h,570°C for 6h,570°C for 12h,and 580°C for 2h,respectively.Correspond-ingly,the GC samples were labeled as GC x _5704h,GC x _5706h,GC x _57012h,and GC x _5802h (x =0and 0.5).To check the composition of the glass samples,energy dis-persive spectra (EDS)were taken with a Philips XL-30FEG (Philips Electron Optics,Eindhoven,Holland)scanning elec-tron microscope equipped with an EDAX DX4i EDS (EDAX Inc.,Mahwah,NJ).The results reveal that a very limited Al 2O 3incorporation and a loss due to evaporation ofB.Dunn—contributing editorManuscript No.32868.Received March 10,2013;approved August 6,2013.†Author to whom correspondence should be addressed.e-mail:qyzhang@3836J.Am.Ceram.Soc.,96[12]3836–3841(2013)DOI:10.1111/jace.12599©2013The American Ceramic SocietyJ ournalﬂuorine while melting,which might be due to the low glass-melting temperature at 1350°C for 1h with the controlled prepared condition (covered corundum crucibles and a small amount of NH 4HF 2additive were used).To follow the thermal behavior of the as-prepared glass,diﬀerential scanning calorimetry (DSC)experiment was car-ried out on the glass powder in nitrogen atmosphere at a heating rate of 10K/min.According to the DSC curve shown in Fig.1,the glass-transition (T g )and crystallization (T c )temperatures are determined to be 565°C and 667°C,respectively.To characterize the GC in terms of phase identi-ﬁcation and microstructures observation,X-ray powder dif-fractometer (XRD)and transmission electron microscope (TEM)measurements were performed using XRD (Philips PW1830,Cu K a )and TEM (JEM-2010,Tokyo,Japan).The Raman spectra were recorded by a Raman spectrometer (HORIBA Jobin-Yvon Inc.,Paris,France)in the region 100–1250cm À1.The glass sample was excited with an argon ion laser at 532nm.The absorption spectra were measured on a Perkin-Elmer Lambada 900UV/VIS/NIR spectropho-tometer (Waltham,MA)in the spectral range 320–3000nm with the resolution of 1nm.Emission spectra were taken on a computer-controlled Triaxial 320spectroﬂourimeter (Jobin-Yvon Inc.)upon excitation with 980nm LD,and the signal was detected with a R928photomultiplier tube (Products for research Inc.,Danvers,MA)for visible emission,InGaAs (800–1650nm)detector for 1.2l m emission and PbSe detec-tor assembled with a Standford SR 510lock-in ampliﬁer (Stanford Research Systems,Sunnyvale,CA)for 2.0l m emission.The decay curves of 1.2l m emission (Ho 3+:5I 6level)were recorded on a high-resolution spectrophotometer (Edinburgh FLSP920;Edinburgh instrument Ltd,Livingston,UK)equipped with a microsecond pulse Xenon (Xe)lamp as the excitation source.While,the decay curves of 2.0l m emission (Ho 3+:5I 7level)were measured by recording the output of the InSb detector with an oscilloscope modulating the 980nm LD excitation sources.All the measurements were performed at room temperature.III.Results and DiscussionFigure 2(a)shows the XRD patterns of PG0and GC0_5802h samples.As can be seen from the ﬁgure,the pre-cursor glass is completely amorphous without any sharp peaks in the pattern,while after heat treatment at 580°C for 2h,the XRD pattern exhibits several intense diﬀraction peaks indexed to the hexagonal LaF 3phase (JCPDS card no.01-076-0510),indicating the successful precipitation of LaF 3nanocrystals among glass matrix.As exhibited in the inset of Fig.2(a),the obtained GC samples keep good transparency.TEM bright ﬁeld image along with the selected-area electron-diﬀraction pattern shown in Fig.2(b)reveals the composite structure of GC with irregular 10-to 20-nm-sized nanocrys-tals distributing in the glassy matrix.The high-resolutionTEM image in Fig.2(c)shows the detailed lattice structure of an individual LaF 3nanocrystal.It can be seen that single particle exhibits crystalline nature with the d-spacing value of3.24 A,in good agreement with the parameter of LaF 3crys-tals in [101]direction.Figure 3shows the absorption spectra of PG0,PG0.5,and GC0samples in the wavelength region 320–3000nm.The absorption bands corresponding to transitions from Yb 3+:2F 7/2ground state to 2F 5/2state and from Ho 3+:5I 8ground state to the respective excited states:5I 7,5I 6,5F 5,(5F 4,5S 2),5F 3,(5F 1,5G 6),and 5G 5were labeled in Fig.3.It is noted that all the absorption transitions exhibit little diﬀer-ence between PG0and GC0samples,except the red shift of ultraviolet (UV)absorption edge for GC0caused bytheFig.1.DSC curve of the blank glass with the composition of 50GeO 2–20Al 2O 3–15LaF 3–15LiF.(a)(b)(c)Fig.2.(a)XRD patterns of the PG0and GC0_5802h samples.The inset shows the optical images of PG0and GC0samples over a printed paper sheet.(b)A typical transmission electron microscope (TEM)bright ﬁeld image of GC0_5802h.The inset shows the corresponding selected-area electron-diﬀraction pattern of the GC0_5802h.(c)High-resolution TEM image of a LaF 3nanocrystal.Fig.3.Absorption spectra of PG0,GC0samples doped with 0.25mol%Ho 2O 3,2mol%Yb 2O 3and PG0.5doped with 0.25mol %Ho 2O 3,2mol%Yb 2O 3and 0.5mol%CeF 3.The inset is the transmission spectra.December 2013Fluorogermanate Glass-Ceramic3837Rayleigh scattering.19,20In comparison with the PG0sample,the red shift of UV-side absorption edge shown in PG0.5sample is associated with the interconﬁgurational transition of Ce 3+ions,i.e.,4f 1:2F 5/2?4f 0,5d 1.21As shown in the inset of Fig.3,the GC samples keep high transmittance in the 2.0l m region,which is important for the application of 2.0l m lasers.Figure 4compares ﬂuorescence spectra of Ho 3+ions in PG0,GC0_5704h,GC0_5706h,and GC0_57012h samples upon the excitation of 980nm LD.As shown in Fig.4,the spectra are characterized by two emission bands at 1.2and 2.0l m,corresponding to the Ho 3+:5I 6?5I 8and 5I 7?5I 8transitions,respectively.As Ho 3+ions have no absorption band at around 980nm,the presence of 1.2and 2.0l m ﬂuo-rescence signals demonstrate the occurrence of energy trans-fer from Yb 3+to Ho 3+.The possible energy-transfer mechanism for Ho 3+/Yb 3+-codoped samples has been depicted in the simpliﬁed energy level diagram (Fig.5).Upon excitation of 980nm LD,Yb 3+ions are initially excited from the ground state (2F 7/2)to the excited state (2F 5/2).Then,Yb 3+ions in the 2F 5/2level transfer their energy to the adjacent Ho 3+ions by a phonon-assisted energy-transfer process (ET1),exciting Ho 3+from the 5I 8ground state to 5I 6excited state.22Ho 3+ions on the 5I 6level will decay radi-atively to the ground state by emitting 1.2l m photons or decay nonradiatively to the 5I 7level where energy is releasedin forms of 2.0l m ﬂuorescence.It is worthwhile to mention that the emission intensity at 1.2and 2.0l m both increases with the increasing heat-treatment time.This may be closely associated with the gradual precipitation of LaF 3nanocrys-tals in glass with the prolongation of heat-treated time.As for the volume fraction of crystalline phase in glass-ceramic,one can roughly evaluate the value from the ratio of the inte-grated area of diﬀraction peaks over the total area under the XRD pattern.9Thus,the volume fraction of crystalline in GC0_5704h,GC0_5706h,and GC0_57012h was estimated to be about 6.26%,9.15%,and 15.88%,respectively.This means that there is an increasing possibility for RE ions to be incorporated into LaF 3nanocrystals with the increase in heat-treatment time.The observed luminescence intensiﬁca-tion could be associated with the reduced nonradiative loss of RE ions within such crystal-like environment with low phonon energy.For a rigorous investigation,the Raman spectra and 1.2l m (Ho 3+:5I 6)decay curves of precursor glass and glass-ceramics were measured.As shown in Fig.6(a),there exist two broad bands in the region 100–1250cm À1,similar to other oxyﬂuoride glass system.23Interestingly,there arise on the broad band (200–700cm À1)one sharp peak at 459cm À1and three weak shoulders centered around 224,285,361cm À1for GC samples.The bands around 224,285,361,and 459cm À1can be ascribed to the lattice vibration of LaF 3.24,25Therefore,the precipitation of LaF 3crystallites is further conﬁrmed by Raman spectroscopy.Moreover,we can recognize that the maximum phonon energy of PG and GC samples is about 884and 842cm À1,respectively.It should be noted that the phonon energy of the area where the crystallites participated should be much lower than 842cm À1.Figure 6(b)exemplarily shows the decay curve of Ho 3+:5I 6level in PG0monitoring at 1192nm,which can be well ﬁtted to double exponential function:I ¼A 1exp ðÀt =s 1ÞþA 2exp =ðÀt =s 2Þ(1)where I is the luminescence intensity monitored at the maxi-mum emission wavelength,A 1and A 2are constants,t is the time,s 1and s 2are rapid and slow lifetimes for exponential ing these parameters,the average decay time s can be determined by the formula:s ¼A 1s 12þA 2s 22ÀÁ=A 1s 1þA 2s 2ðÞ(2)It should be mentioned that 1.2l m emission in the corre-sponding GC samples also exhibit a double exponential decay and the ﬁtting ﬁnally gives the average decay times depicted in the inset of Fig.6(b).Obviously,the lifetime of(a)(b)Fig.4.Emission spectra of the investigated PG0and GC0samples doped with 0.25mol%Ho 2O 3,2mol%Yb 2O 3in the (a)1.2l m and (b)2.0l m region excited with 980nm laserdiode.Fig.5.The Ho 3+–Yb 3+–Ce 3+ions energy level diagram and energy-transfer processes excited by the 980nm laser diode.(a)(b)Fig.6.(a)The Raman spectra of PG0and GC0samples,(b)the decay curve monitored at 1192nm and the double exponential ﬁtting curve.The inset of (b)shows the dependence of Ho 3+:5I 6lifetime on the heat-treated time.3838Journal of the American Ceramic Society—Zhang et al.Vol.96,No.125I 6state shows a monotonous increase with the prolongation of heat-treatment time.Generally,the decay rate for an excited state derived from the measured decay lifetime s m is composed of two terms:the intrinsic radiative decay rate (s R )and the nonradiative decay rate (s NR ),primarily due to mul-tiphonon deexcitation of the excited state.In the absence of concentration quenching eﬀects,they are related according tothe formula:1s m ¼1s Rþ1s NR .26As the multiphonon relaxation rate exhibits a great dependence on the phonon energy of the host matrix,the prolonged lifetime of 1.2l m emission could be related to the reduced multiphonon relaxation rates as a result of the incorporation of RE ions into the low phonon energy environment provided by LaF 3nanocrystals in GC samples.27It should be pointed out that the decay time of 5I 7state obtained after ﬁtting 2l m luminescence decay curve to a single exponential function is relatively less sensitive to the heat-treatment time.There is a slight increase in the lifetime from 6.22ms up to 7.26ms after prolonging the heat-treat-ment time of PG0sample even up till 12h.This could be attributed to the fact that the energy gap between 5I 7and 5I 8(~5000cm À1)is much larger than the counterpart (~3500cm À1)between 5I 6and 5I 7.Furthermore,the upconversion luminescence of Yb 3+/Ho 3+couple in the PG and GC0_5704h samples were pared with the PG sample,the emission inten-sity in GC0_5704h increases greatly and for further analysis,the upconversion luminescence were normalized at 650nm (Fig.7).As illustrated in Fig.7,three upconversion emission bands centered at 538,650,and 745nm were detected upon 980nm excitation,corresponding to Ho 3+:5S 2,5F 4?5I 8,5F 5?5I 8,and 5S 2,5F 4?5I 7radiative transitions,respec-tively.28Moreover,there appears a 478nm (Ho 3+:5F 2,3?5I 8)blue upconversion emission band in GC0_5704h which cannot be observed in the PG sample.In addition,as clearly seen in the Fig.7,the ratio of I 538nm /I 650nm and I 745nm /I 650nm in GC0_5704h is greater than the counterpart of PG sam-ple.The relevant possible upconversion emission mechanism can be proposed with the help of energy level schemes shown in Fig.5.22,29As aforementioned,the successive energy trans-fer from Yb 3+to Ho 3+ions can populate the 5I 6and 5I 7level of Ho 3+ions.One part of Ho 3+ions on 5I 6level can be further excited to 5S 2,5F 4level by way of energy transfer (ET1)and excited state absorption (ESA)processes.Ions on 5S 2,5F 4level will decay nonradiatively to 5F 5level or decay radiatively by generating 538nm green emission and 745nm emission.Moreover,ions on 5S 2/5F 4level can be excited to the 3H 5,6level by ESA process followed by nonradiative decay to 5F 2,3level,where electrons can experience radiative transition to the ground state,yielding 478nm photons.Sim-ilarly,the ET1and ESA processes can promote the Ho 3+ions from the 5I 7level to the 5F 5level where the 650nm red upconversion emission was produced.The upconversion mechanism indicates that the 538and 745nm emission inten-sity relies on the population of 5S 2,5F 4state,whereas the 650nm emission is sensitive to the population of 5F 5state.In GC samples,a part of RE ions are readily coupled into LaF 3nanocrystals with phonon energy much lower than the O –Ge and O –Al bands,12,30resulting in the lowed nonradia-tive decay rate through multiphonon relaxation and the strong upconversion emission in GC samples.Moreover,the lowed nonradiative decay rate means that the nonradiative processes 5S 2,5F 4?5F 5,and 5I 6?5I 7were suppressed.After ET1and ESA energy-transfer process,more electrons are populated on the 5S 2,5F 4state rather than on 5F 5state,which accounts for the result that the ratio of I 538nm /I 650nm and I 745nm /I 650nm in GC0_5704h is greater than the counter-part of PG sample.In addition,the appearance of 478nm in GC can also be ascribed to the lowed nonradiative decay rate.To some extent,however,the reduced nonradiative rate leads to the depopulation of 5I 7level,which prohibits further enhancement of 2.0l m emission.Hence,Ce 3+was intro-duced in the following with the expectation to suppress the energy loss processes.Figure 8illustrates the emission spectra of GC0_5704h and GC0.5_5704h in the 1.2l m [Fig.8(a)]and 2.0l m [Fig.8(b)]region upon 980nm excitation.It is found that the introduc-tion of Ce 3+ions induces an obvious enhancement in 2.0l m emission and reduction in the 1.2l m emission.As there is an approximation in energy between Ho 3+:5I 6?5I 7and Ce 3+:2F 5/2?2F 7/2transitions,the ET2process of 2F 5/2(Ce3+)+5I 6(Ho 3+)?2F 7/2(Ce 3+)+5I 7(Ho 3+)(Fig.5)can take place via phonon-assisted energy-transfer process.16,31It is worth noting that the ET2process can transfer populations from the 5I 6state to 5I 7state,thus promoting the 2.0l m emission at the cost of 1.2l m ﬂuorescence.Based on the pho-non sideband theory minutely discussed in Refs.[11,17],the energy-transfer coeﬃcients from Yb 3+to Ho 3+in GC0_5704h and GC0.5_5704h were calculated and listed in Table I.It is noted that the energy transfer between Yb 3+and Ho 3+is phonon-assisted process.After the addition of Ce 3+ions,the calculated energy-transfer coeﬃcient C Yb –Ho increases from 1.58910À40to 3.62910À40cm 6/s,which indicates the more eﬃcient energy transfer of Yb 3+?Ho 3+in Yb 3+/Ho 3+/Ce 3+triply doped systems.This is similar to the result reported in Ref.[17].Figure 9shows the decay curves of the 1.2l m (Ho 3+:5I 6)and 2.0l m (Ho 3+:5I 7)emission in PG samples.For 1.2l m emission,the decay curves can be well ﬁtted to adoubleFig.7.Upconversion spectra of PG0and GC0_5704h samples doped with 0.25mol%Ho 2O 3,2mol%Yb 2O 3.(a)(b)parison of emission spectra of GC0_5704h and GC0.5_5704h in the (a) 1.2l m and (b) 2.0l m region excited by 980nm laser diode.December 2013Fluorogermanate Glass-Ceramic 3839exponential function.The average decay time s estimated using Eq.(2)is illustrated in the inset of Fig.9as a function of Ce 3+concentration.While the decay curves of 2.0l m emission ﬁt well to a single exponential function.As shown in the inset of Fig.9,there is a drastic decrease in 5I 6lifetime with the addition of Ce 3+ions at low doping level,whereas the 5I 7lifetime experiences very little change.Further increase in Ce 3+concentration over 1mol%causes a signiﬁ-cant decrease in lifetimes of both 5I 6and 5I 7levels.It is found that the introduction of Ce 3+ions induces an obvi-ous enhancement in 2.0l m emission and reduction in the 1.2l m emission.As there is an approximation in energy between Ho 3+:5I 6?5I 7and Ce 3+:2F 5/2?2F 7/2transi-tions,the ET2process of 2F 5/2(Ce 3+)+5I 6(Ho 3+)?2F 7/2(Ce3+)+5I 7(Ho 3+)can take place via phonon-assisted energy-transfer process as shown in Fig.5.It is worth noting that the ET2process can transfer populations from the 5I 6state to 5I 7state,thus promoting the 2.0l m emission at the cost of 1.2l m ﬂuorescence.Table II presents the emission cross section (Ho 3+:5I 7?5I 8)calculated using Fuchtbauer –Ladenburg equation,32the calculated spontaneous radiative transition probabilities A rad (Ho 3+:5I 7)and the measured lifetime s m (Ho 3+:5I 7)of the PG samples with diﬀerent Ce 3+concentration.As can be seen from the table,the r emis and A rad increase slightly with the increase in Ce 3+concentration.The A rad of this glass system is larger than that of ﬂuorophosphates glass (80.56s À1)17but is smaller than that of tellurite glass (136.00s À1).18It’s worth noting that the quantum eﬃciency g (s m 9A rad )is compara-ble to the ﬂuorophosphate (FP)glass.17The inﬂuence of Ce 3+on upconversion emissions of Ho 3+in PG x (x =0,0.25,0.5, 1.0,and 2.0)samples is exhibited in Fig.10.The upconversion emissions decrease with the increase ini Ce 3+concentration.As shown in the inset of Fig.10,the intensity ratio I 538nm /I 650nm almost fol-lows a liner decrease with the increment of Ce 3+concentra-tion.The variation in I 538nm /I 650nm is closely related totheFig.9.The decay curves and the corresponding ﬁtting curves of 1.2l m (Ho 3+:5I 6)and 2.0l m (Ho 3+:5I 7)emission for PG samples.The inset shows the dependence of lifetime on the Ce 3+concentration.Table I.Calculated Microscopic Parameters of the ET Processes in GC0_5704h and GC0.5_5704hEnergy transfer Samples N (N phonons-assist process)C D –A 10À40(cm 6/s)C D –D 10À40(cm 6/s)012Yb ?Yb (2F 5/2,2F 7/2?2F 7/2,2F 5/2)GC0_5704h 95.89% 4.11%––62.54GC0.5_5704h 97.29% 2.71%––59.74Yb ?Ho (2F 5/2?5I 6)GC0_5704h 081.19%18.81% 1.58–GC0.5_5704h 061.87%38.13% 3.62–Table II.r emis ,A rad ,s m ,g of Ho 3+:5I 7in Various Glass SystemSamplesr emis 910À21(cm 2)A rad (s À1)s m (ms)g (%)ReferencesPG0 4.75103.84 6.2264.59Present workPG0.25 4.80105.64 6.0964.34PG0.5 4.94109.02 5.8964.21PG1.0 5.03111.89 4.9755.61PG2.0 5.06114.12 4.2848.84FPC0 4.6673.540.948 6.9717FPC10 4.7680.560.9127.3517FP 7.9090.42 5.6050.6417Silicate 7.0061.650.32 1.9717Fluoride 5.3058.0726.70155.0017Germanate –111.58––33TNZ glass –136.00%1.60%21.7618Fig.10.Upconversion spectra of PG x (x =0,0.25,0.5,1.0,2.0)under 980nm laser diode excitation.The inset shows the intensity ratio of I 538nm /I 650nm as a function of Ce 3+ions.3840Journal of the American Ceramic Society—Zhang et al.Vol.96,No.12phonon-assisted ET2process between Ho3+and Ce3+.As discussed beforehand,the phonon-assisted ET2process can transfer population from the intermediate green-emitting state(5I6)to the intermediate red-emitting state(5I7).In that way,there will be more electrons accumulated on5F5state rather than5S2,5F4state,directly leading to the red (650nm)emission intensiﬁcation at the cost of green (538nm)emission.IV.ConclusionIn summary,eﬃcient1.2and2.0l m infrared emissions as well as typical upconversionﬂuorescence of Ho3+at538and 650nm have been achieved inﬂuorogermanate glass and GC through Yb3+sensitization.The enhanced luminescence and lengthened lifetime for5I6state after crystallization of the precursor glass can be ascribed to the reduced nonradiative rate beneﬁted from the low phonon energy environment for some RE ions incorporated into LaF3nanocrystals.To impede the energy loss processes such as upconversion lumi-nescence and/or1.2l m emission,Ce3+was introduced and veriﬁed to be eﬀective in enhancing the2.0l mﬂuorescence and suppressing the concurrent emissions.AcknowledgmentsThis work was supported by the National Science Foundation of China(grant nos.51125005and U0934001)and the Chinese Ministry of Education(grant no.20100172110012).References1S.W.Henderson, C.P.Hale,J.R.Magee,M.J.Kavaya,and A.V.Huﬀaker,“Eye-Safe Coherent Laser Radar System at2.1l m Using Tm, Ho:YAG Lasers,”Opt.Lett.,16[10]773–5(1991).2B.Richards,S.Shen,A.Jha,Y.Tsang,and D.Binks,“Infrared Emission and Energy Transfer in Tm3+,Tm3+-Ho3+and Tm3+-Yb3+-Doped Tellurite Fibre,”Opt.Express,15[11]6546–51(2007).3Q.Wang,J.Geng,T.Luo,and S.Jiang,“Mode-Locked2l m Laser with Highly Thulium-Doped Silicate Fiber,”Opt.Lett.,34[23]3616–8(2009).4V.A.Mikhailov,Y.D.Zavartsev,A.I.Zagumennyi,V.G.Ostroumov, P.A.Studenikin,E.Heumann,G.Huber,and I.A.Shcherbakov,“Tm3+: GdVO4-a New Eﬃcient Medium for Diode-Pumped2-l m Lasers,”Quantum Electron.,27[1]13–4(1997).5K.Driesen,V.K.Tikhomirov,C.G€o rller-Walrand,V.D.Rodriguez,and A.B.Seddon,“Transparent Ho3+-Doped Nano-Glass-Ceramics for Eﬃcient Infrared Emission,”Appl.Phys.Lett.,88[7]73111–3(2006).6C.J.Lee,G.Han,and N.P.Barnes,“Ho:Tm Lasers.II:Experiments,”IEEE J.Quantum Electron.,32[1]104–11(1996).7S.D.Jackson,A.Sabella,A.Hemming,S.Bennetts,and ncaster,“High-Power83W Holmium-Doped Silica Fiber Laser Operating with High Beam Quality,”Opt.Lett.,32[3]241–3(2007).8Y.Tsang, B.Richards, D.Binks,J.Lousteau,and A.Jha,“A Yb3+/ Tm3+/Ho3+Triply-Doped Tellurite Fibre Laser,”Opt.Express,16[14] 10690–5(2008).9Q.J.Chen,W.J.Zhang,Q.Qian,Z.M.Yang,and Q.Y.Zhang,“Spec-troscopic Investigation of2.02l m Emission in Ho3+/Tm3+Codoped Trans-parent Glass Ceramic Containing CaF2Nanocrystals,”J.Appl.Phys.,107[9] 93511–5(2010).10Q.C.Sheng,X.L.Wang,and D.P.Chen,“Enhanced Broadband2.0l m Emission and Energy Transfer Mechanism in Ho-Bi Co-Doped Borophosphate Glass,”J.Am.Ceram.Soc.,95[10]3019–21(2012).11W.J.Zhang,Q.J.Chen,Q.Qian,and Q.Y.Zhang,“The1.2and2.0l m Emission from Ho3+in Glass Ceramics Containing BaF2Nanocrystals,”J.Am.Ceram.Soc.,95[2]663–9(2012).12Y.Wang and J.Ohwaki,“New Transparent Vitroceramics Codoped with Er3+and Yb3+for Eﬃcient Frequency Upconversion,”Appl.Phys.Lett.,63 [24]3268–70(1993).13D.Q.Chen,Y.S.Wang,F.Bao,and Y.L.Yu,“Broadband Near-Infra-red Emission from Tm3+/Er3+Co-Doped Nanostructured Glass Ceramics,”J.Appl.Phys.,101[11]113511–6(2007).14M.Mortier,“Between Glass and Crystal:Glass–Ceramics,a New Way for Optical Materials,”Philos.Mag.B,82[6]745–53(2002).15N.C.Chang,J.B.Gruber,R.P.Leavitt,and C.A.Morrison,“Optical Spectra,Energy Levels,and Crystal Field Analysis of Tripositive Rare Earth Ions in Y2O3.I.Kramers Ions in C2Sites,”J.Chem.Phys.,76[8]3877–89 (1982).16G.Dantelle,M.Mortier,D.Vivien,and G.Patriarche,“Eﬀect of CeF3 Addition on the Nucleation and Up-Conversion Luminescence in Transparent Oxyﬂuoride Glass-Ceramics,”Chem.Mater.,17[8]2216–22(2005).17Y.Tian,R.R.Xu,L.Y.Zhang,L.L.Hu,and J.J.Zhang,“Enhanced Eﬀect of Ce3+Ions on2l m Emission and Energy Transfer Properties in Yb3+/Ho3+ Doped Fluorophosphate Glasses,”J.Appl.Phys.,109[8]083535–40(2011).18L.L.Tao,Y.H.Tsang,B.Zhou,B.Richards,and A.Jha,“Enhanced 2.0l m Emission and Energy Transfer in Yb3+/Ho3+/Ce3+Triply Doped Tel-lurite Glass,”J.Non-Cryst.Solids,358[14]1644–8(2012).19C.L.Yu,J.J.Zhang,L.Wen,and Z.H.Jiang,“New Transparent Er3+-Doped Oxyﬂuoride Tellurite Glass Ceramic with Improved Near Infrared and up-Conversion Fluorescence Properties,”Mater.Lett.,61[17]3644–6(2007). 20Z.Pan,A.Ueda,M.Hays,R.Mu,and S.H.Morgan,“Studies of Er3+ Doped Germanate-Oxyﬂuoride and Tellurium-Germanate-Oxyﬂuoride Trans-parent Glass-Ceramics,”J.Non-Cryst.Solids,352[8]801–6(2006).21X.C.Yu,F.Song,W.T.Wang,L.J.Luo,C.G.Ming,Z.Z.Cheng, L.Han,T.Q.Sun,H.Yu,and J.G.Tian,“Eﬀects of Ce3+on the Spectro-scopic Properties of Transparent Phosphate Glass Ceramics Co-Doped With Er3+/Yb3+,”mun.,282[10]2045–8(2009).22L.Feng,J.Wang,Q.Tang,L.F.Liang,H.B.Liang,and Q.Su,“Optical Properties of Ho3+-Doped Novel Oxyﬂuoride Glasses,”J.Lumin.,124[2] 187–94(2007).23L. A.Bueno,Y.Messaddeq, F. A.Dias Filho,and S.J.L.Ribeiro,“Study of Fluorine Losses in Oxyﬂuoride Glasses,”J.Non-Cryst.Solids,351 [52]3804–8(2012).24H.H.Caspers,R.A.Buchanan,and H.R.Marlin,“Lattice Vibrations of LaF3,”J.Chem.Phys.,41[1]94–9(1964).25R.P.Bauman and S.Porto,“Lattice Vibrations and Structure of Rare-Earth Fluorides,”Phys.Rev.,161[3]842–7(1967).26R.Chen,Y.Q.Shen,F.Xiao,B.Liu,G.G.Gurzadyan,Z.L.Dong, X.W.Sun,and H.D.Sun,“Surface Eu-Treated ZnO Nanowires with Eﬃ-cient Red Emission,”J.Phys.Chem.C,114[42]18081–4(2010).27T.Miyakawa and D.L.Dexter,“Phonon Sidebands,Multiphonon Relax-ation of Excited States,and Phonon-Assisted Energy Transfer Between Ions in Solids,”Phys.Rev.B,1[7]2961–9(1970).28L.Q.An,J.Zhang,M.Liu,and S.W.Wang,“Preparation and Upcon-version Properties of Yb3+,Ho3+:Lu2O3Nanocrystalline Powders,”J.Am. Ceram.Soc.,88[4]1010–2(2005).29Y.M.Yang,M.X.Zhang,Z.P.Yang,and Z.L.Fu,“Violet and Visible Up-Conversion Emission in Yb3+-Ho3+Co-Doped Germanium-Borate Glasses,”J.Lumin.,130[10]1711–6(2010).30A.S.Gouveia-Neto,L.A.Bueno,A.C.M.Afonso,J.F.Nascimento, E.B.Costa,Y.Messaddeq,and S.J.L.Ribeiro,“Upconversion Lumines-cence in Ho3+/Yb3+and Tb3+/Yb3+-Codoped Fluorogermanate Glass and Glass Ceramic,”J.Non-Cryst.Solids,354[2–9]509–14(2008).31G.Y.Chen,H.C.Liu,G.Somesfalean,H.J.Liang,and Z.G.Zhang,“Upconversion Emission Tuning from Green to Red in Yb3+-Ho3+-Codoped NaYF4Nanocrystals by Tridoping with Ce3+Ions,”Nanotechnology,20[38] 385704–10(2009).32T.Schweizer,D.W.Hewak,B.N.Samson,and D.N.Payne,“Spectro-scopic Data of the1.8-,2.9-,and4.3-l m Transitions in Dysprosium-Doped Gallium Lanthanum Sulﬁde Glass,”Opt.Lett.,21[19]1594–6(1996).33W.J.Zhang,D.C.Yu,J.P.Zhang,Q.Qian,S.H.Xu,Z.M.Yang,and Q.Y.Zhang,“Near-Infrared Quantum Splitting in Ho3+:LaF3Nanocrystals Embedded Germanate Glass Ceramic,”Opt.Mater.Express,2[5]636–43 (2012).hDecember2013Fluorogermanate Glass-Ceramic3841。

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Simple route to Nd:YAG transparent ceramics Yu. A. Barnakov*, I. Veal, Z. Kabato, G. Zhu, M. Bahoura, M. A. Noginov Center for Materials Research, Norfolk State University, 700 Park Avenue, Norfolk, 23504 VA

We report on the fabrication and spectroscopic characterization of transparent Nd3+:YAG ceramic, a prospective material for future laser applications.

Keywords: Transparent laser ceramics, Nd:YAG, solid-state laser materials

INTRODUCTION Neodymium doped Yttrium Aluminum Garnet (Nd:YAG) has proven to be one of the best solid-state laser materials in the history of quantum electronics. Its indisputable dominance in a broad variety of laser applications is determined by a combination of high emission cross section with long spontaneous emission life-time, high damage threshold, mechanical strengths, high thermal conductivity and consequently low thermal distortion of the laser beam, etc. The fact that the Czochralski crystal growth of Nd:YAG is a matured, highly reproducible and relatively easy technological procedure adds significantly to the value of this material. One of the few drawbacks of Nd:YAG is its relatively low growth rate, ~1 mm/hour, making the production of large laser rods and slabs, with the linear size comparable to 10 inches or more, which are needed for high-power and high-energy laser applications, prohibitively expensive.

The later disadvantage stimulated tremendous efforts for alternative synthesis methods. The pioneering research of several groups in Japan in the last decade [1-4] has led to the development of the unique technique allowing one to synthesize highly transparent polycrystalline ceramics of YAG and several other laser materials [5].

Large ceramic laser elements can be produced at relatively low cost, they are free of internal stress or intrinsic birefringence, and allow relatively large doping levels or optimized custom-designed doping profiles. This makes ceramic laser elements particularly important for high-energy laser applications. Thus, 1.46 kW Nd:YAG ceramic laser has been demonstrated [6]. These ceramics are commercially produced by Konoshima Chemical Co. Ltd. in Japan. At the same time, several research groups in the US and Europe, working on the technology of the same material [7-11], were not able to produce laser ceramics of comparable quality.

CERAMIC FABRICATION The research program undertaken in the Center for Materials Research at Norfolk State University is aimed at understanding the fundamental principles underlying fabrication of transparent ceramics. We study the relationship between chemical synthesis, processing, microstructure, and optical properties of the ceramics as well as optimize each step of the processes: the synthesis of nanoparticles, the compaction of a green body, and the vacuum sintering. At the present time, we report our recent breakthrough from translucency to transparency in Nd doped YAG ceramics.

Commercially available powders of nominally 2 at.% doped Nd:YAG nanoparticles were used in the experiments. Various additives, including traditional alkylsilanes (TEOS, APTMS) and polymers (PVA, PVB), taken in concentrations 1-5 wt.%, were employed to modify particles’ surface and facilitate the compaction. Green body compaction was performed in several different ways with the use of a uniaxial press (22 MPa), cold isostatic press (CIP, up to 330 MPa), and traditional slip casting approach. In the latter method, the powders were re-dispersed in methanol at the presence of additives and then sedimentated naturally in a plastic vial.

*ybarnakov@nsu.edu. In different particular experiments, the green body density varied in the range 0.2-0.6 of its maximal value (4.56 g/cm3) characteristic of grown single-crystal YAG [12]. The highest value 56% was obtained for a green body formed via precipitation followed by air-drying. The vacuum sintering of compacted pellets was performed in several steps characterized by different durations and temperatures. The objectives of different particular stages were (i) the removal of impurities, (ii) the reduction of pores, and (iii) the grain growth. At the latter stage, the ceramic was processed at 1700-1800oC for few hours at the vacuum better than 10–6 torr (10-3 Pa).

CHARACTERIZATION OF OPTICAL PROPERTIES The logo of Norfolk State University can be clearly seen through the sample of fabricated Nd:YAG ceramic (thickness ~0.3 mm), Figure 1. The Scanning Electron Microscope (SEM) image of the same sample shows granules with the average size 3-5 µm, Figure 2.