Fabrication and Luminescent Properties of Nd31-Doped Lu2O3

Transparent Ceramics by Pressureless Sintering

Ding Zhou, Ying Shi,w Jianjun Xie, Yuying Ren, and Ping Yun

School of Material Science and Engineering, Shanghai University, Shanghai 20072, China

The fabrication of transparent Nd31

ion-doped Lu2O3 ceramicsis investigated by pressureless sintering under a flowing H2 at-mosphere. The starting Nd-doped Lu2O3 nanocrystalline pow-der is synthesized by a modified coprecipitant processing using aNH4OH1NH4HCO3 mixed solution as the precipitant. Thethermal decomposition behavior of the precipitate precursor isstudied by thermogravimetric analysis and differential thermalanalysis. After calcination at 10001C for 2 h, monodispersedNd31:Lu2O3 powder is obtained with a primary particle size ofabout 40 nm and a specific surface area of 13.7 m

2/g. Green

compacts, free of additives, are formed from the as-synthesizedpowder by dry pressing followed by cold isostatic pressing.Highly transparent Nd31:Lu2O3 ceramics are obtained afterbeing sintered under a dry H2 atmosphere at 18801C for 8 h. Thelinear optical transmittance of the polished transparent sampleswith a 1.4 mm thickness reaches 75.5% at the wavelength of1080 nm. High-resolution transmission electron microscopy ob-servations demonstrate a ‘‘clear’’ grain boundary between adja-cent grains. The luminescent spectra showed that the absorptioncoefficient of the 3 at.% Nd-doped Lu2O3 ceramic at 807 nmreached 14 cm�1, while the emission cross section at 1079 nmwas 6.5� 10

�20cm

2.

I. Introduction

SINCE the 1950s, when Coble fabricated the first translucentalumina ceramic,1 many kinds of translucent and transpar-

ent ceramics have been developed, including Al2O3,1 Y2O3,

2–4

Sc2O3,5 Lu2O3,

6,7 Y3Al5O12 (YAG),8–10 MgAl2O4,11 and

AlON,12 etc. These materials are promising candidates for op-tical applications, such as luminous pipes for high-intensity dis-charge lamps, heat-resistant windows, and polycrystallinescintillators for radiation detection. Moreover, transparent ce-ramic has aroused great interest on the aspect of a solid-statelaser since Ikesue and colleagues reported the fabrication of atransparent Nd:YAG laser ceramic via vacuum sintering.8,10

Compared with single-crystal ceramics, transparent ceramicshave many advantages, such as better chemical homogeneity,lower fabrication temperatures, the feasibility of larger sizes,and, especially, a higher doping concentration of the activateions, which leads to the high possibility of a higher power laseroutput.13,14 Ichiro Shoji et al.15 reported a laser output by usinga 3.4 at.% Nd:YAG ceramic, which operates at an outputpower 2.3 times higher than that of a 0.9 at.% Nd-doped coun-terpart. In the Nd:YAG ceramics system, the emission quantumefficiency (Zq) decreases with the Nd concentration (CNd), withan unfavorable effect on the emission threshold. However, thisdecrease is not strong enough to annihilate the effect of the in-

creasing pump absorption efficiency at high Nd-doping concen-trations, and the product ZqCNd could be taken as a figure ofmerit for the laser potential of these materials, reaching themaximum at around 3 at.% Nd-doping in the YAG system,16

which stimulates us to fabricate the Nd:Lu2O3 transparent ce-ramics with a high doping concentration.

Lutetia (Lu2O3) is one of the attractive sesquioxides withan isotropic cubic crystal structure (Th7 space group), ex-tremely high density (9.42 g/cm3), high thermal conductivity(12.5 W/mK), and a wide band gap (B6.4 eV), which favor itsapplications not only as scintillators for radiation detection butalso as a promising host material for laser gain media.17,18 Withthe advantages of ceramic powder processing and sintering tech-nologies, transparent Lu2O3 ceramics have been fabricated viacombustion synthesis combined with vacuum sintering.7 In2002, Lu and colleagues reported a 0.15 at.% Nd:Lu2O3 laserceramic,18 where the starting powders were synthesized by ho-mogeneous precipitation from urea and the densification wascarried out by vacuum sintering. In 2005, Takaichi et al.19 re-ported a highly efficient laser output using Yb31:Lu2O3 ceramic,but there was no detailed description on the optical propertiesand microstructure of transparent Lu2O3 ceramics.

In this paper, we report the fabrication of the Nd31-dopedLu2O3 transparent ceramics using nanocrystalline Nd31:Lu2O3

powder by pressureless sintering under a reducing atmosphere.The characteristics of the as-prepared precursor, synthesized by amodified coprecipitation processing method, are evaluatedby thermogravimetric analysis and differential thermal analysisequipped with mass spectroscopy (TG-DTA-MS) and Fouriertransform infrared (FTIR) spectra determinations. Highly trans-parent Nd31:Lu2O3 ceramics are fabricated by pressurelesssintering at 18801C for 8 h under a flowing H2 atmosphere with-out any additives. The optical properties and microstructure ofthe as-sintered transparent samples are characterized in detail.The absorption and emission cross sections of as-fabricated sam-ple are calculated based on the measured luminescent spectrum.

II. Experimental Procedure

The starting raw materials used were commercial Lu2O3 andNd2O3 powders (purity 499.99%, Xiyuan International,Shanghai, China). An aqueous solution of Lu(NO3)3 andNd(NO3)3 was prepared by dissolving the oxide powders intoan analytical reagent HNO3 solution according to the formulaNd0.06Lu1.94O3. The precursor for nanosized Nd:Lu2O3 powderwas prepared by adding a NH4OH1NH4HCO3 mixed precip-itant (molar ratio 1:4) to a 0.1M lutetium nitrate solution at arate of 3 mL/min. The ultimate pH value of the suspension waskept in the range of 8–9, making sure that all the rare earthcations (Lu31, Nd31) had been deposited into precipitate pre-cursors. After being aged for 24 h, the amorphous precursor wasfiltered using a suction filter, washed four to five times withdeionized water and twice with alcohol, and then dried at 801Cfor 24 h in air. After being crushed and sieved to 120 meshes, theprecursor was calcined and transformed into crystalline nano-powders in a muffle furnace at 10001C with a heating rate of21C/min.

G. Wei—contributing editor

This work was financially supported by the Natural Science Foundation of China (No.50572115) and the Basic Research Key Project of Shanghai Municipal (06JC14029).Shanghai Leading Academic Disciplines (S30107).

wAuthor to whom correspondence should be addressed. e-mail: yshi@shu.edu.cn

Manuscript No. 25226. Received September 16, 2008; approved May 4, 2009.

Journal

J. Am. Ceram. Soc., 92 [10] 2182–2187 (2009)

DOI: 10.1111/j.1551-2916.2009.03190.x

r 2009 The American Ceramic Society

2182

Nd31:Lu2O3 green compacts were formed by dry pressingunder a pressure of 30 MPa in a stainless-steel die and cold iso-statically consolidated under a pressure of 200 MPa. The ther-mal shrinking behavior was investigated by a thermal expansionanalyzer (DIL402C NETZSCH, Selb, Germany) from roomtemperature to 14001C (101C/min). The density of the compactswas determined from the initial bulk density and the measuredlinear shrinkage from room temperature to 14001C in air by thefollowing equation:5

r ¼ r0=ð1� DL=L0Þ3 (1)

where r is the density of the square columnar compact of spe-cific temperatures, r0 (4.7 g/cm3) is the initial density ofthe green compact after cold isostatic pressing, and DL/L0 isthe linear shrinkage rate under different temperatures. Densifi-cation of the green compact was performed in a furnace (ModelFDB-14-19, NEMS Co., Tokyo, Japan) equipped with a tung-sten-mesh heater by pressureless sintering under a flowing, dryH2 atmosphere at 18801C for 8 h. The bulk density of the sin-tered specimens was determined by the Archimedes method.

The thermal decomposition behaviors of the precursor werecharacterized on a TG-DTA-MS apparatus (STA 449C, NET-ZSCH). FTIR spectroscopy spectra were recorded by an infra-red spectrometer (1725X, Perkin Elmer, Waltham, MA) on KBrpellets in the region of 4000–400 cm�1 with 4 cm�1 resolutionunder ambient conditions. Phase composition identification wasperformed with an X-ray diffractometer (D/max-2550, Rigaku,Tokyo, Japan) equipped with graphite monochromatized CuKaradiation (l5 1.5406 A, 40 kV/200 mA) in the range of 2y5101–701. The specific surface area of nanosized Nd31:Lu2O3

powder was measured on a multipoint Brunauer–Emmett–Teller (Tristar 3000, Micromeritics, Atlanta, GA). The micro-structure of the Nd31:Lu2O3 powder and the sintered transpar-ent ceramics were observed by field emission scanning electronmicroscopy (SEM, JSM-6700F, JEOL, Tokyo, Japan) andhigh-resolution transmission electron microscopy (HRTEM,JEM2010F, JEOL, Tokyo, Japan). The linear optical transmit-tance of transparent Lu2O3 ceramics was measured over thewavelength region of 190–1100 nm on a UV/Vis/NIR spectro-photometer (Lambda 2, Perkin Elmer, Waltham, MA). Theemission spectrum of the specimen pumped by the 808 nm LDwas recorded by a spectrofluorometer (Fluorolog-3, JobinYvon, Edision, Longjumeau, France) equipped with a Hama-matsu (Shizuoka, Japan) R928 photomultiplier tube at roomtemperature.

III. Results and Discussion

Figure 1 shows the TG-DTA-MS curves of the precursor ob-tained from complex precipitation processing. The precursor

reveals a continuous thermal decomposition from room tem-perature until 7001C, with a total weight loss of about 34.65%.Combined with the analysis of MS curves inset, it is deducedthat the exothermal peak at around 951C corresponds to therelease of hydration water and OH�. In addition, the MS curveinset (m/z5 44) indicates that the exothermic peak at about6561C resulted from the decomposition of the carbonate,6 whichconfirms that the precipitate precursor derived from theNH4OH1NH4HCO3 precipitant is composed of basic lutetiumcarbonate.

The FTIR spectra of the resultant precursor and its calcinatedproducts (10001C/2 h) are illustrated in Fig. 2. The broad ab-sorption band at 3430 cm�1 is attributed to the coupled effectsof molecular water and free hydroxyl groups.5 The two intensepeaks at 1522 and 1402 cm�1 are assigned to the asymmetricstretch of the C–O bond in CO3

2�, while the peaks at 1090 and846 cm�1 are due to the symmetric stretch of C–O and thedeformation vibration of C–O in CO3

2�, respectively.6 Theseabsorption peaks indicate the presence of carbonate groups inthe resultant precursor, which coincides with the results of MSdetermination. Furthermore, the new absorption band near 578cm�1 is attributed to the characteristic stretching of the Lu–Obond, resulting from the crystallization of Lu2O3 from the pre-cursor.20 The characteristics of amorphous precursors are ingood agreement with the results we have obtained in theEu:Lu2O3 system

6.

Fig. 1. TG-DTA-MS curves of the Nd31:Lu2O3 precursors pre-pared with a mixture of NH4OH1NH4HCO3 (molar ratio 1:4) as theprecipitant.

Fig. 2. Fourier transformed infrared spectra of the precipitate precur-sor and the 3 at.% Nd31:Lu2O3 powder calcined at 10001C for 2 h.

Fig. 3. X-ray diffraction patterns of the as-prepared powders calcinedat various temperatures.

October 2009 Fabrication and Luminescent Properties of Nd31-Doped Lu2O3 2183

X-ray diffraction (XRD) patterns of the precursor powderscalcined at various temperatures are shown in Fig. 3. After beingcalcined at 7001C for 2 h, the precursor has transformed into acubic crystalline Lu2O3 phase (JCPDS65-3172), and no othercrystalline phase is detected. From the profiles of XRD patternsobtained from different conditions, it is indicated that the powderexhibits improved crystallinity as the calcination temperature in-creases from 8001 to 10501C, owing to crystalline particle growth.

Figure 4 presents the dependence of the specific surfacearea (SBET) and the corresponding particle size (dBET) of theNd31:Lu2O3 powder on the calcination temperatures from 8501to 11001C. Accompanied with the raising of the calcinationtemperature from 8501 to 11001C, SBET reveals a sharp decreasefrom 22 to 9 m2/g, corresponding to the increase of the meanparticle size from 25 to 75 nm.

Figure 5 shows the SEM micrograph and TEM micrographof the Lu2O3 powder calcined at 10001C. Both SEM and TEMobservations demonstrate a monodispersed morphology withthe spherical particle shape and a primary particle size of about40 nm. The bright spots shown in Fig. 5(b) are likely caused byirradiation damage during TEM observation. It is suggestedthat the introduction of CO3

2� is essential to obtain nanosizedLu2O3 powders with a satisfied dispersion state, which arisesfrom the release of CO2 around 7001C during the decompositionof the carbonate, preventing the adjacent particles from severeagglomeration, to some extent.

In order to evaluate the sinterability of the Nd31:Lu2O3-nanosized powder, the densification behavior is investigated bydetermining the thermal linear shrinkage curve from room tem-perature to 14001C in air. After dry press forming and coldisostatic pressing, the density of the green compact is about

4.7 g/cm3. It is shown in Fig. 6 that the compact shows no re-markable change in linear shrinkage and bulk density when thetemperature is below 9001C. Once the heating temperature ex-ceeds 9001C, the compact exhibits rapid densification. At a tem-perature of 14001C, the linear thermal shrinkage reached amaximum value of 17%. In the meantime, the relative densityof the compact attained 89% theoretical density of Lu2O3. Con-sidering the high melting point of Lu2O3 (24501C), it is suggestedthat the nanocrystalline powder from the complex precipitantexhibited quite good sinterability, which is likely to be fullydensified by pressureless sintering.

Figure 7(a) presents the appearance of the 3 at.%Nd31:Lu2O3 transparent ceramic, which has been mechanicallypolished on both sides. The sintered specimen has a diameter of14 mm and a thickness of 1.4 mm, with a relative density of99.7% theoretical density measured by the Archimedes method.Figure 7(b) shows the optical linear transmittance of the ceramicon the wavelength range from 200 to 1100 nm. The transmit-tance of a pure Lu2O3 polycrystalline ceramic, fabricated by thesame route, is given as a contrast, which indicates that all theabsorption bands are caused by Nd-ions in the measured wave-length. From the 3 at.% Nd31:Lu2O3 curve, it can be seen thatthe optical transmittance enhanced rapidly as the wavelengthincreased from 300 to 500 nm. In the wavelength range of 600–800 nm, the linear transmittances of the specimen can achieve ahigh level of approximately 65%–70%. As the wavelength goesbeyond 1000 nm, the polished specimen (1.4 mm in thickness)exhibits a linear optical transmittance value of 75.5% (theoret-

Fig. 4. Dependences of the specific surface area (SBET) and the corre-sponding particle size (dBET) of Nd31:Lu2O3 powders on the calcinationtemperatures.

Fig. 5. (a) Scanning electron micrograph and (b) transmission electron micrograph microstructure of the as-prepared Lu2O3 powder calcined at10001C for 2 h.

Fig. 6. Dependence of relative density of the Nd31:Lu2O3 compact ontemperatures, under a heating rate of 101C/min (inset: linear thermalshrinkage from room temperature to 14001C).

2184 Journal of the American Ceramic Society—Zhou et al. Vol. 92, No. 10

ical transmittance of Lu2O3 is 81.7%). According to the follow-ing equation, the linear optical transmittances (T) are dependenton the optical attenuation coefficient (a) of transparent ceramicsand the thickness (t):

T ¼ I=I0 ¼ ð1� RÞ2 expð�atÞ (2)

where R5 (n�1)2/(n11)2, in which n5 1.9 is the refraction in-dex for Lu2O3 ceramics. From the linear optical transmittanceof 75.5% of the specimen at 1079 nm, it can be calculated thatthe optical attenuation coefficient for the as-preparedNd31:Lu2O3 transparent ceramic is 0.056 mm�1.

Figure 8 presents the SEM micrograph of the polished andfractured surfaces of the Nd31:Lu2O3 transparent ceramic. Itcan be demonstrated from Fig. 8(a) that the crystalline size ofthe transparent Nd31:Lu2O3 ceramic is about 50 mm, and noabnormal grain growth is observed. The morphology inFig. 8(b) proves that the fracture mode of Nd31:Lu2O3 trans-parent ceramics is mainly transgranular. Micropores still can berandomly observed in Fig. 8, which might lead to the degrada-tion of optical transmittance in the visible wavelength.

It is well recognized that the residual pores and impurities atgrain boundaries play an important role in influencing the op-tical transmittances of transparent ceramics. The TEM micro-graphs shown in Figs. 9(a) and (b) present the typicalmicrostructure morphology of Nd31:Lu2O3 transparent ceram-ics, demonstrating that there is no secondary impuritiessegregation at grain boundaries or triple junctions. The high-resolution micrograph in Fig. 9(c) reveals the lattice image ofadjacent Lu2O3 grains clearly, which further confirms that noresidual impurity and interphase existed at the grain boundary.

The interplanar spacings of upper grain, as shown in Fig. 9(c),are 0.42 and 0.33 nm, respectively, corresponding to the inter-planar spacings of the ð1�1�2Þand ð01�3Þ crystal planes, while thelower grain shows the lattice image of the (113) crystal plane.The width of the grain boundary is estimated to be as thin as 0.5nm. It is believed that the microstructural features of ourNd31:Lu2O3 transparent ceramics are quite favorable for reduc-ing scattering losses arising from inhomogeneity in polycrystal-line ceramics.

Figure 10 shows the absorption and fluorescence spectra ofthe as-fabricated 3 at.% Nd-doped Lu2O3 ceramic pumped atthe 808 nm wavelength. From Fig. 10(a), the absorption band at807 nm has a full-width at half-maximum of 4 nm, which is amuch wider bandwidth compared with a typical Nd:YAG ce-ramic, with a sharp absorption line (o1 nm). Based on the flu-orescence spectrum pumped by the 808 nm LD, the emissioncross section (sem), as shown in Fig. 11, is calculated by theFuchtbauer–Ladenburgas equation,

semðlÞ ¼l5bJJ0IðlÞ

8pn2ctrRIðlÞldl (3)

where b is the fluorescence branch ratio, I(l) is the intensity ofthe emission spectrum, trad is the fluorescence lifetime of theupper level, and n5 1.9 is the refractive index of the Lu2O3 ma-terial. The main emission peak is located at a wavelength of 1079nm, corresponding to a maximum emission cross section (sem)of 6.5� 10�20 cm2, which is quite close to the value of 9� 10�20

cm2 reported by Lu.18 In order to implement laser oscillation inthe future, the optical polishing and necessary coating are un-derway for 3 at.% Nd31-doped Lu2O3 transparent ceramics.

Fig. 7. (a) Transparent sample of the Nd31:Lu2O3 transparent ceramic (1.4 mm thick); (b) inline optical transmittance curves of the transparent sample.

Fig. 8. (a) Scanning electron micrograph image of the polished and thermally etched surface; (b) fracture surface of the Nd31:Lu2O3 transparentceramic sintered at 18801C for 8 h.

October 2009 Fabrication and Luminescent Properties of Nd31-Doped Lu2O3 2185

IV. Conclusions

Highly sinterable, monodispersed 3 at.% Nd:Lu2O3 powderswith a primary particle size of 40 nm have been preparedvia a modified coprecipitant processing method using aNH4OH1NH4HCO3 mixed solution as precipitant. After be-ing formed by dry pressing and cold isostatic pressing, the greencompacts have been fully densified at 18801C for 8 h under a

flowing H2 atmosphere. The mechanically polished Nd31:Lu2O3

ceramic (1.4 mm thickness) achieves 75.5% transmittance at awavelength of 1080 nm. The transparent sample with a crystallitesize of about 50 mm shows an intercrystalline fracture. A ‘‘clean’’grain boundary without impurity phases is observed byHRTEM, which is beneficial to the improvement of optical trans-mittance of the Lu2O3 ceramic. According to the luminescent

Fig. 9. Microstructures of transparent Nd31:Lu2O3 ceramics: (a) transmission electron micrograph (TEM) image of the grain boundary between twoLu2O3 grains; (b) TEM image of the triple junction; (c) HRTEM lattice image of the grain boundary.

Fig. 10. (a) Room temperature absorption spectrum of the 3 at.% Nd:Lu2O3 ceramic; (b) fluorescence spectrum of the specimen pumped by the808nm LD.

2186 Journal of the American Ceramic Society—Zhou et al. Vol. 92, No. 10

spectra of the 3 at.% Nd-doped Lu2O3 specimen, the emissioncross section at 1079 nm is 6.5� 10�20 cm2.

Acknowledgements

The authors gratefully acknowledge the Analysis and Testing Center of Shang-hai University for technical support and Ms. M. L. Ruan from Shanghai Instituteof Ceramics, Chinese Academy of Science, for high-resolution TEMmeasurement.

References

1R. L. Coble, ‘‘Transparent Alumina and Method of Preparation’’; U.S. Patent,No. 3026210, March 20, 1962.

2C. Greskovich and J. P. Chernoch, ‘‘Polycrystalline Ceramic Laser,’’ J. Appl.Phys., 44, 4599–606 (1973).

3C. Greskovich and J. P. Chernoch, ‘‘Improved Polycrystalline Ceramic La-sers,’’ Appl. Phys., 45 [10] 4495–502 (1974).

4Z. G. Huang, X. D. Sun, Z. M. Xiu, S. W. Chen, and C. T. Tsai, ‘‘PrecipitationSynthesis and Sintering of Yttria Nanopowders,’’Mater. Lett., 58, 2137–42 (2004).

5J. G. Li, T. Ikegami, and T. Mori, ‘‘Fabrication of Translucent, Sintered Sc2O3

Ceramics,’’ J. Am. Ceram. Soc., 88 [4] 817–21 (2005).6Q. W. Chen, Y. Shi, L. Q. An, S. W.Wang, J. Y. Chen, and J. L. Shi, ‘‘A Novel

Co-Precipitation Synthesis of a New Phosphor Lu2O3:Eu3,’’ J. Eur. Ceram. Soc.,

27, 191–7 (2007).7E. Zych, D. Hreniak, W. Strek, L. Kepinski, and K. Domagala, ‘‘Sintering

Properties of Urea-Derived Lu2O3-Based Phosphors,’’ J. Alloys. Compd., 341,391–4 (2002).

8A. Ikesue, I. Furusato, and K. Kamata, ‘‘Polycrystalline Transparent YAGCreamics by a Solid-State Reaction Method,’’ J. Am. Ceram. Soc., 78 [1] 225–8(1995).

9J. G. Li, T. Ikegami, J. H. Lee, and T.Mori, ‘‘Low-Temperature Fabrication ofTransparent Yttrium Aluminum Garnet (YAG) Ceramics Without Additives,’’ J.Am. Ceram. Soc., 83 [4] 961–3 (2000).

10A. Ikesue, Y. L. Kang, T. Taira, T. Kamimura, and K. Yoshida, ‘‘Progress InCeramic Lasers,’’ Annu. Rev. Mater. Res., 36, 397–429 (2006).

11J. G. Li, T. Ikegami, J.-H. Lee, and T. Mori, ‘‘Fabrication of TranslucentMagnesium Aluminum Spinel Ceramics,’’ J. Am. Ceram. Soc., 83 [11] 2866–8(2000).

12J. Cheng, D. Agrawal, Y. Zhang, and R. Roy, ‘‘Microwave Reactive Sinteringto Fully Transparent Aluminum Oxynitride (AlON) Ceramics,’’ J. Mater. Sci.Lett., 20, 77–9 (2001).

13A. Ikesue, T. Kinoshita, K. Kamata, and K. Yoshida, ‘‘Fabrication and Op-tical Properties of High-Performance Polycrystalline Nd:YAG Ceramics for SolidState Lasers,’’ J. Am. Ceram. Soc., 78 [4] 1033–40 (1995).

14A. Ikesue, K. Kamata, and K. Yoshida, ‘‘Effects of Neodymium Concentra-tion on Optical Characteristics of polycrystalline Nd:YAG Laser Ceramics,’’ J.Am. Ceram. Soc., 79 [7] 1921–6 (1996).

15I. Shoji, S. Kurimura, Y. Sato, T. Taira, A. Ikesue, and K. Yoshida, ‘‘OpticalProperties and Laser Characteristics of Highly Nd31-Doped Y3Al5O12 Ceramics,’’Appl. Phys. Lett., 77 [7] 939–41 (2000).

16V. Lupei, A. Lupei, and N. Pavel, ‘‘Laser Emission Under Resonant Pump inthe Emitting Level of Concentrated Nd:YAG Ceramics,’’ Appl. Phys. Lett., 79 [5]590–2 (2001).

17U. Griebner and V. Petrov, ‘‘Passively Mode-Locked Yb:Lu2O3 Laser,’’ Opt.Express, 12 [14] 3125–30 (2004).

18J. Lu, K. Takaichi, T. Uematsu, A. Shirakawa, M. Musha, and K. Ueda,‘‘Promising Ceramic Laser Material: Highly Transparent Nd31:Lu2O3 Ceramic,’’Appl. Phys. Lett., 81 [23] 4324–6 (2002).

19K. Takaichi, H. Yagi, A. Shirakawa, K. Ueda, S. Hosokawa, T. Yanagitani,and A. Kaminskii, ‘‘Lu2O3:Yb31 Ceramics—a Novel Gain Material for High-Power Solid-State Lasers,’’ Phys. Stat. Sol. (a), 202 [1] R1–3 (2005).

20N. T. McDevitt and W. L. Baun, ‘‘Infrared Absorption Study of Metal Oxidesin the Low Frequency Region (700-240 cm�1),’’ Spectrochim. Acta, 20 [5] 799–808(1964). &

Fig. 11. Emission cross section of the 3 at.% Nd:Lu2O3 transparentceramic.

October 2009 Fabrication and Luminescent Properties of Nd31-Doped Lu2O3 2187