The luminescence properties of the high-density phosphor Lu1−xNdxTaO4

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The luminescence properties of High-density phosphor Lu1-xNdxTaO4 Yiping Zhao, Qingli Zhang, Changxin Guo, Chaoshu Shi, Fang Peng, Huajun Yang, Dunlu Sun, Jianqiao Luo, Wenpeng Liu

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S0022-2313(14)00301-9 http://dx.doi.org/10.1016/j.jlumin.2014.05.018 LUMIN12703

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Cite this article as: Yiping Zhao, Qingli Zhang, Changxin Guo, Chaoshu Shi, Fang Peng, Huajun Yang, Dunlu Sun, Jianqiao Luo, Wenpeng Liu, The luminescence properties of High-density phosphor Lu1-xNdxTaO4, Journal of Luminescence, http://dx.doi.org/10.1016/j.jlumin.2014.05.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The luminescence properties of high-density phosphor Lu1-xNdxTaO4 Yiping Zhao1, Qingli Zhang1,*, Changxin Guo2, Chaoshu Shi2, Fang Peng1,3, Huajun Yang1,3, Dunlu Sun1, Jianqiao Luo1, Wenpeng Liu1 (1 The Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031 PR China) (2 Department of Physics, University of Science and Technology of China, Hefei 230026, China) (3 University of Chinese Academy of Sciences, Beijing, 100049 PR China)

Abstract A promising new type inorganic scintillation material M′-type Lu1-xNdxTaO4 was successfully synthesized by solid reaction method. Its structure was determined by Rietveld refinement to the X-ray diffraction data. The calculated density of Lu1-xNdxTaO4 is 9.53-9.67g cm-3, which is the greatest among current inorganic scintillators. Upon light excitation at 355nm, the dominated emissions of Nd3+ were 4D3/2→4I13/2 and 4D3/2→4I15/2. The concentration dependences of the fluorescence intensity and fluorescence lifetime of 4

D3/2→4I13/2 emission in Lu1-xNdxTaO4 were presented. It was inferred that the optimal doping

concentration of Nd3+ was about 5.4% and the fluorescence lifetime of 4D3/2→4I13/2 emission in the zero concentration limit was about 263.2ns. It is suggested to be a potential heavy scintillator due to its high density and fast luminescence decay. Keywords: Nd:LuTaO4; crystal structure; luminescence; concentration quenching 1. Introduction Inorganic scintillation crystals have been used in many fields, from high energy physics to nuclear medical imaging [1, 2]. Scintillation is luminescence caused by ionizing radiation *

Corresponding author. Tel./fax: +86-551-5591039, E-mail address: [email protected]

(X-rays, α, β, γ-rays, etc.)[3]. High density and stopping power (i.e., large effective atomic number) are important for reducing the amount of scintillator material needed because they can enhance the absorbing of ionizing radiation. In the past several decades, some important inorganic scintillation crystals have been developed, such as[4,5] NaI:Tl (3.67g cm-3), CsI:Tl (4.51g cm-3), BaF2 (4.88g cm-3), Bi4Ge3O12 (7.1g cm-3), PbWO4 (8.28g cm-3), YAlO3:Ce (5.6g cm-3), LuAlO3:Ce (8.34g cm-3), Y3Al5O12:Ce (4.56g cm-3), Lu3Al5O12:Ce (6.67g cm-3), Gd2SiO5:Ce (6.7g cm-3), Lu2SiO5:Ce (7.4g cm-3), LaBr3:Ce (5.3g cm-3). However, the densities of all the materials are less than 9g cm-3. Lutetium tantalate (LuTaO4) is an efficient luminescence host material, especially if excitation occurs by ionizing radiation [6]. LuTaO4 also has outstandingly high density (9.81g cm-3). It may be an excellent scintillator when doped with proper active ions. Ce3+ and Pr3+ are most commonly used active ions in scintillators because their fast 4fn-15d-4f n emission, but no[6, 7] or only very weak[8] 4fn-15d-4f n emission was found in Ce3+ or Pr3+ doped tantalates. It maybe owe to the 4fn-15d energy levels of Ce3+ and Pr3+ are located in or near the conduction band of tantalate[7]. The 4fn-4fn emissions of some rare earth elements activated tantalates were also studied, Pr3+, Eu3+, Tb3+ doped LuTaO4 showed efficient luminescence[9-13], while the luminescence of

Sm3+, Dy3+, Tm3+ doped LuTaO4

was weak[13]. But the fluorescence lifetime of these emissions has been investigated little. In previous work of our lab [14], the fluorescence lifetimes of 613nm emission corresponding to Eu3+ 5D0→7F2 transition in Lu0.96Eu0.04TaO4 and 547nm emission corresponding to Tb3+ 5D4→7F5 transition in Lu0.96Tb0.04TaO4 were determined as 1.51ms and 1.04ms, respectively. These lifetimes were too long for scintillators. In this work, Nd3+ was used as activator. M′-type Lu1-xNdxTaO4 was synthesized by solid reaction method. Its structure, photoluminescence, decay time and concentration quenching properties were studied in details, which were not reported so far to our knowledge. It was found that its fluorescence lifetime of 418.5nm emission corresponding to Nd3+ 4D3/2→4I13/2 transition was about 263.2ns. LuTaO4 activated by Nd3+ may be a promising inorganic scintillation material with high density and short lifetime.

2. Experiment Lu1-xNdxTaO4 (x=0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.10) were prepared by solid-state reaction method using Lu2O3 (99.99%), Ta2O5 (99.99%), Nd2O3 (99.999%) as starting materials. Firstly, the raw materials were weighted accurately according to appropriate stoichiometric ratio and then mixed and ground in a mortar. Secondly, the mixed powders were heated up to 1500°C with heat rate about 2.3°C/min and calcined at 1500°C for 24h. Lastly, the calcined samples were slowly cooled to room temperature and followed by careful grinding. The structure of obtained polycrystalline powders were examined by Philips X′pert PRO X-ray diffractometer with Cu Kα radiation (λ= 0.15406 nm) operated at 40 kV and 40mA. A scan step of 0.02° was applied to record the patterns in the 2θ range 15°-80°. Room temperature excitation, emission spectra and the fluorescence decay curves were measured using Edingburger FLS-920 spectrometer. Low temperature excitation, emission spectra were measured using JY Fluorolog-3-Tou spectrometer. The excitation lamp used in excitation, emission spectra measuring is a continuous Xenon arc lamp. The excitation lamp used in decay curves measuring is an nF920 nanosecond flash lamp, the rise time of which is about 2 ns and the cut off time of which is about 4 ns. The detectors are photomultipliers whose dark count rate is less than 5 counts per second. 3. Results and discussion 3.1. Crystal structure LuTaO4 usually exhibits two crystal structures, one belonging to I2/a (M-type), the other P2/a (M′-type). The XRD patterns of our Lu1-xNdxTaO4 samples, as shown in Fig. 1, indicate all samples have translated into single M′-type LuTaO4 phase (ICDD cards #24-1263) through solid-state reaction. The Rietveld refinements of powder XRD data were carried out with GSAS program [15]. Fig. 2 shows the Rietveld refinement plot of Lu0.95Nd0.05TaO4 (wRp=0.0722, Rp=0.0559). The refined lattice parameters and the refined atomic fractional coordinates of Lu1-xNdxTaO4 are given in Table 1, Table 2 respectively. As can be seen, the

lattice parameters (a, b, c) and cell volume increase with the increase of doping concentration of Nd3+ because the radius of Nd3+ (1.00 Å) is larger than that of Lu3+ (0.85 Å), the density decreases with the increase of doping concentration of Nd3+ because the cell volume increases and the atomic weight of Nd (144.24) is less than that of Lu (174.967). 3.2. Luminescence properties Fig. 3 shows the excitation and emission spectra of Lu0.95Nd0.05TaO4.The excitation spectrum (λem = 418.5 nm) was recorded from 250 nm to 380nm. There are three excitation bands which are due to 4I9/2→4D1/2+4D5/2+4D3/2, 4I9/2→2I11/2+4D7/2+2I13/2+2L15/2, 4I9/2→2D3/2 [16, 17]. The emission spectrum (λex = 355 nm) was recorded from 400 nm to 600nm. Upon excitation at 355nm (4I9/2→4D5/2), emissions from 4D3/2→4I13/2, 4D3/2→4I15/2, 2P3/2→4I15/2 transitions were observed [16, 17]. Among them, the emission at 418.5nm corresponding to 4

D3/2→4I13/2 transition is the most intensive. Fig 4 shows the excitation and emission fine

structure of Lu0.95Nd0.05TaO4, which were measured with a scan step of 0.1 nm at 8K and room temperature. At 8K, only transitions from ground Stark level of one manifold to Stark levels of another manifold are observed. Twenty-one stark levels of 4I13/2, 4I15/2, 4D3/2, 4D5/2 and 4

D1/2 can be identified through 8K spectra, which are given in Table 3. At 300K, transitions

from excited Stark levels such as Z2, Z3 and P2 are also observed. Additionally, there is a shift to lower energy (longer wavelength) observed in comparing the 300 K spectra to the 8 K spectra. 3.3. Luminescence decay There are both fast component and slow component in experimental decay curve of 418.5 nm emission. In order to distinguish where the two components are from, the decay curves of different emission wavelength centered 406.5nm, 420.0nm and 434.5nm (Δλ=10nm) were measured, which were shown in Fig. 5. The decay curve of 420.0nm emission can be fitted by a fast component and a slow component, while the decay curves of 406.5nm emission and 434.5nm emission can be fitted only by one fast component. These decay curves were measured under the same exposure time. The total counts of fast component are 6780 of

406.5nm, 5437 of 420.0nm, 4166 of 434.5nm, respectively, which agree well with the intensity of the baseline in emission spectra. Moreover, the lifetime of all the fast components is close to that of exciting light. It was concerned that 4D3/2→4I13/2 emission locates at 418.5nm, which is included in the decay curve of emission centered 420nm. So it can be deduced that the fast component was due to the scattering of exciting light, the slow component was due to 4D3/2→4I13/2 emission of Nd3+. Additionally, we investigated the luminescence of many other materials upon excitation at 355nm, such as MgO powder, Y2O3 powder, Nd:YAG (Y3Al5O12) crystal and Nd:GGG (Gd3Ga5O12) crystal. A fast component similar to that of Lu1-xNdxTaO4 powder was observed in all the powder samples including nonluminous materials but not observed in crystal samples. It confirmed that the fast component was due to the scattering of exciting light on powder samples. In order to get more accurate lifetime of 4D3/2→4I13/2 emission, we set the measuring range of emission wavelength to 418nm-419nm. After deconvolution, the decay curves were well fitted using two exponential function. The logarithm scaled luminescence decay curves of Lu1-xNdxTaO4 were shown in Fig.6. The fast component was removed from the graph because it has not physical meaning in this paper. Additionally, the decay curves were translated in order to easily compare their slope. 3.4. Concentration quenching properties The lifetime of 4D3/2→4I13/2 emission obtained by fitting decreases with the increase of doping concentration because of self-quenching. Based on the Dexter model for dipole-dipole interactions [18], the self-quenching was well described by [19, 20]

τ=

τ0 1 + β x2

(1) Where τ is lifetime observed, τ0 is lifetime in the zero concentration limit, x is the concentration of Nd3+, β is a constant represents the intensity of self-quenching. Fig. 7 shows the concentration dependence of fluorescence lifetime values. The theoretical curve (solid

curve) was performed using Eq. (1) with τ0 and β as adjustable parameters. It indicates that the lifetime in the zero concentration limit is about 263.2ns. When exciting light reached the surface of powder samples, diffuse reflection and abosorption occurred at the same time. The basis of the diffuse reflectance theory used to quantify the concentration of an absorbing material in a nonabsorbing matrix was Kubelka-Munk equation [21, 22].

F ( R)

(1 − R ) = 2R

2

=

K S

(2)

where R is the absolute diffuse reflectance of the sample at infinite depth. K is the absorption coefficient, which is approximately proportional to the concentration (x) of absorbing material in low concentration. S is the scattering coefficient, which is approximately a constant in low concentration. So F(R) is proportional to the concentration.

F ( R) ∝ x

(3)

Olinger and Griffiths [23] proposed that the best linear representation of an absorbing material concentration is given by log (1/R) (absorbance) in the case of strongly absorbing matrices.

⎛1⎞ log ⎜ ⎟ ∝ x ⎝R⎠

(4)

Considering the self-quenching of Nd3+, the fluorescence intensity can be described by

I = Ia ×

(1 − R ) 1 + β x2

(5)

Where Ia is the ideal fluorescence intensity when the absorbance is infinity and there is no self-quenching. In this work, we find Eq. (4) agrees better with experiment than Eq. (3) through the fitting of experiment data used Eq. (5) substituting Eq. (4) or Eq. (3) for R. So the

concentration dependence of the fluorescence intensity as shown in fig.8 can be described by

I=

(

I a 1 − e −α x 1+ β x

)

2

(6)

Where α is the ratio of absorbance to Nd3+ concentration. When the maximum fluorescence intensity is reached, the percentage of doping concentration is about 5.4. It can be regarded as the optimal doping concentration. 4. Conclusions Lu1-xNdxTaO4 with single M′-type phase was successfully synthesized by solid reaction method. Upon excitation at 355nm, the dominated emissions of Nd3+ from 400nm to 600nm are 4D3/2→4I13/2 and 4D3/2→4I15/2. The fluorescence lifetime of 4D3/2→4I13/2 emission in the zero concentration limit is about 263.2ns and the optimal doping concentration of Nd3+ is about 5.4%. The density of Lu1-xNdxTaO4 calculated using the refined lattice parameters is more than 9.5 g cm-3, which is the greatest among current inorganic scintillators. Results show that LuTaO4 doped with Nd3+ is a potential scintillator with high density and short lifetime. Acknowledgement This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 51172236 and 91122021). Reference [1] S K Kim, H J Kim and Y D Kim. New Journal of Physics 12 (2010) 075003. [2] Rainer Novotny. Nuclear Instruments and Methods in Physics Research A 537 (2005) 1-5. [3] M.J. Weber. Nuclear Instruments and Methods in Physics Research A 527 (2004) 9-14. [4] L.A. Andryushchenko, B.V. Grinev, and V.A. Tarasov. Instruments and Experimental Techniques, 54 (2011)603-631. [5] Martin Nikl. Meas. Sci. Technol. 17 (2006) R37-R54. [6] G. Blasse, G.J. Dirksen, L.H. Brixner, M.K. Crawford. Journal of Alloys and Compounds, 209 (1994) 1-6. [7] W.J. Schipper, M.F. Hoogendorp, and G. Blasse. Journal of Alloys and Compounds, 202 (1993) 283-287. [8] M.J. Weber, S.E. Derenzo, C. Dujardin, W.W. Moses. Presented at SCINT ‘95, Delft, The

Netherlands, LBL-37789. [9] I.D. Arellano, M.V. Nazarov, J.A. Corte, Ahmad Fauzi M.N.. Journal of Luminescence 132 (2012) 2479–2483. [10] Bo Liua, Kun Han, Xiaolin Liu, Mu Gu, Shiming Huang, Chen Ni, Zeming Qi, Guobin Zhang. Solid State Communications 144 (2007) 484-487. [11] Xiaolin Liu, Kun Han, Mu Gu, Shiming Huang, Bo Liu, Chen Ni. Applied Surface Science 255 (2009) 4680-4683. [12] Kun Han, Mu Gu, Xiaolin Liu, Chen Ni, Shiming Huang, Bo Liu. Proceedings of SPIE Vol. 6984(2008)69841E. [13] Bo Li, Zhennan Gu, Jianhua Lin, Mian-Zeng Su. Materials Research Bulletin 35 (2000) 1921-1931. [14] Wenpeng Liu, Qingli Zhang, Lihua Ding, Dunlu Sun, Jianqiao Luo, Shaotang Yin. Journal of Alloys and Compounds 474 (2009) 226-228. [15] A.C. Larson and R.B. Von Dreele. Los Alamos National Laboratory Report LAUR 86-748 (2004). [16] John B. Gruber, Marian E. Hills, Toomas H. Allik, et al. Phys. Rev. B 41(12): 7999-8012(1990). [17] Janne-Mieke Meijer, Linda Aarts, Bryan M. van der Ende, Thijs J. H. Vlugt, and Andries Meijerink. Phys. Rev. B 81, 035107 (2010). [18] C. Jacinto, T. Catunda, D. Jaque, and J. G. Sole. Phys. Rev. B 72, 235111(2005). [19] A. S. de Camargo, C. Jacinto, L. A. Nunes, T. Catunda, D. Garcia et al. Journal of applied physics 101, 053111 (2007). [20] C. Jacinto, S. L. Oliveira, L. A. O. Nunes, J. D. Myers, M. J. Myers, and T. Catunda. Phys. Rev. B 73, 125107 (2006). [21] P. Kubelka, F. Munk. Z. Tech. Phys., 12, 593(1931). [22] P. Kubelka. J. Opt. Soc. Am., 38, 448(1948). [23] V. A. Matyshak, O. V. Krylov. Catal. Today, 25, 1-87(1995).

Table 1. The refined lattice parameters of M′-Lu1-xNdxTaO4 obtained by Rietveld refinement. samples

a(Å)

b(Å)

c(Å)

α(°)

β(°)

γ(°)

V(Å3)

Density (g cm-3)

Lu0.99 Nd0.01TaO4

5.2523

5.4397

5.0728

90

96.092

90

144.117

9.670

Lu0.98 Nd0.02TaO4

5.2532

5.4411

5.0736

90

96.095

90

144.200

9.657

Lu0.97 Nd0.03TaO4

5.2551

5.4428

5.0752

90

96.105

90

144.339

9.641

Lu0.96 Nd0.04TaO4

5.2571

5.4452

5.0768

90

96.109

90

144.503

9.623

Lu0.95 Nd0.05TaO4

5.2587

5.4475

5.0783

90

96.112

90

144.649

9.606

Lu0.94 Nd0.06TaO4

5.2599

5.4484

5.0793

90

96.122

90

144.733

9.593

Lu0.92 Nd0.08TaO4

5.2631

5.4520

5.0819

90

96.131

90

144.989

9.562

Lu0.90 Nd0.10TaO4

5.2665

5.4561

5.0849

90

96.142

90

145.273

9.530

Table 2. The refined atomic fractional coordinates of M ′-Lu1-xNdxTaO4 obtained by Rietveld refinement. samples

lattice site

x/a

y/b

z/c

Lu0.99 Nd0.01TaO4

Ta1 Lu1/Nd1 O1 O2

0.250000 0.250000 0.511895 0.379482

0.303923 0.768977 0.598639 0.068000

0.000000 0.500000 0.244656 0.272604

Lu0.98 Nd0.02TaO4

Ta1 Lu1/Nd1 O1 O2

0.250000 0.250000 0.507503 0.388519

0.304211 0.769372 0.585704 0.074229

0.000000 0.500000 0.250211 0.268358

Lu0.97 Nd0.03TaO4

Ta1 Lu1/Nd1 O1 O2

0.250000 0.250000 0.508357 0.382697

0.303916 0.769613 0.590737 0.073020

0.000000 0.500000 0.247074 0.270182

Lu0.96 Nd0.04TaO4

Ta1 Lu1/Nd1 O1 O2

0.250000 0.250000 0.507208 0.381257

0.304049 0.769933 0.588007 0.070080

0.000000 0.500000 0.248083 0.268620

Lu0.95 Nd0.05TaO4

Ta1 Lu1/Nd1 O1 O2

0.250000 0.250000 0.508520 0.387108

0.304531 0.769577 0.590022 0.075557

0.000000 0.500000 0.249126 0.271484

Lu0.94 Nd0.06TaO4

Ta1 Lu1/Nd1 O1 O2

0.250000 0.250000 0.509779 0.385407

0.304176 0.770790 0.586702 0.079396

0.000000 0.500000 0.244462 0.272948

Lu0.92 Nd0.08TaO4

Ta1 Lu1/Nd1 O1 O2

0.250000 0.250000 0.509089 0.383590

0.304995 0.769392 0.593326 0.068613

0.000000 0.500000 0.249537 0.265783

Lu0.90 Nd0.10TaO4

Ta1 Lu1/Nd1 O1

0.250000 0.250000 0.504206

0.304466 0.770530 0.582983

0.000000 0.500000 0.242778

O2

0.388667

0.079202

0.267152

Table 3. Energy levels of Nd3+ in LuTaO4 2S+1

E(cm-1)

LJ

4

I13/2

4

I15/2

X1 X2 X3 X4 X5 X6 X7 W1 W2 W3 W4

3583 3606 3628 3714 3900 3945 4028 5518 5532 5566 5653

2S+1

E(cm-1)

LJ

4

D3/2

4

D5/2

4

D1/2

Fig. 1. The powder XRD profile of Lu1-x NdxTaO4.

W5 W6 W7 W8 P1 P2 Q1 Q2 Q3 Q4

5829 5862 5918 5956 27563 27663 27886 28043 28233 28345

Lu0.90Nd0.10TaO4 Lu0.92Nd0.08TaO4

Intensity(a.u.)

Lu0.94Nd0.06TaO4

Lu0.95Nd0.05TaO4 Lu0.96Nd0.04TaO4

Lu0.97Nd0.03TaO4

Lu0.98Nd0.02TaO4

Lu0.99Nd0.01TaO4 15

30

45

2θ(degree)

60

75

Fig. 2. Rietveld refinement of the powder XRD profile of Lu0.95 Nd0.05TaO4. The observed data, calculated data, background and difference profiles are displayed.

Intensity(a.u.)

obs. background calc. diff.

15

20

25

30

35

40

45

50

2θ(degree)

55

60

65

70

75

80

Fig. 3. Excitation spectrum (λem = 418.5 nm) and emission spectrum (λex = 355 nm) of Lu0.95Nd0.05TaO4. The peaks marked with “*” were caused by stray light.

1000000 4

4

D3/2 I13/2

4

4

D1/2+ D5/2

800000

4

Intensity(a.u.)

+ D3/2 600000 2

I11/2+

4

D7/2+

2

I13/2+

400000

4

4

D3/2 I15/2

2

L15/2

2

* D3/2 2

200000

* 0 250

4

P3/2 I15/2

300

350

400

**

450

Wavelength(nm)

* ** 500

550

600

350 355 Z1

Z1 Q3 354.9

Q4 353.3

360

(d)

365 415 (e)

420

Wavelength(nm) 425 450 455

P1 W5 460.1 P1 W6 460.8 P1 W7 462.0 P1 W8 462.8

P1 W1 453.6 P1 W2 453.9 P1 W3 454.6 P1 W4 456.4

P1 X5 422.6 P1 X6 423.4 P1 X7 424.9

P1 X1 417.0 P1 X2 417.4 P1 X3 417.8 P1 X4 419.3

Z1 P2 361.5 P1 362.8

(b)

P2 W1 451.9 P2 W2 452.2 P2 W3 452.9 P1 W1 454.2 W2 454.6 P1 P1 W3 455.2 P1 W4 457.0 P2 W7 459.0 P2 W8 460.1 P1 W5 460.7 P1 W6 461.2 P1 W7 462.4 P1 W8 463.2

Q2 356.6

Q1 358.6

Z1

Z1

Z1

Z1 Q4 352.8 Z1 Q3 354.2

(a)

P2 X2 416.0 P2 X3 416.6 P1 X1 417.9 P1 X2 418.3 P1 X3 418.7 P1 X4 420.3 P2 X6 422.5 P1 X5 423.6 P1 X6 424.5 P1 X7 426.0

Q2 357.0 Z1 Q1 359.0 Z2 Q1 360.6 Z1 P2 362.0 Z1 P1 363.2 Z2 P2 363.6 Z2 P1 364.7 Z3 P2 365.2 Z3 P1 366.9

Z1

Intensity(a.u.)

Fig. 4 The excitation and emission fine structure of Lu0.95Nd0.05TaO4. (a)8K λem = 418.5 nm (b)8K λex = 355 nm (c) 8K λex = 355 nm (d)300K λem = 418.5 nm (e)300K λex = 355 nm (f)

300K λex = 355 nm

(c)

(f)

460

Fig. 5. The logarithm scaled luminescence decay curves of different range of emission wavelength in Lu0.95Nd0.05TaO4 excited by 350nm-360nm light of a nanosecond pulsed hydrogen discharge flashlamp. The inset figure is the emission spectra of Lu0.95Nd0.05TaO4.

Lu0.95Nd0.05TaO4

1000

Intensity(a.u.)

405.5nm 420.0nm 434.5nm exciting light

400

410 420 430 Wavelength(nm)

440

Counts

100

10

1 0

200

400

600

Time(ns)

800

1000

Fig. 6. The logarithm scaled luminescence decay curves of Lu1-xNdxTaO4.

experiment data

fitting curve

Counts

100

Lu0.99Nd0.01TaO4 Lu0.98Nd0.02TaO4 Lu0.97Nd0.03TaO4 Lu0.96Nd0.04TaO4 Lu0.95Nd0.05TaO4 Lu0.94Nd0.06TaO4 Lu0.92Nd0.08TaO4 Lu0.90Nd0.10TaO4

10 100

200

300

Time(ns)

400

500

Fig. 7. The concentration dependence of fluorescence lifetime of 4D3/2→4I13/2 emission.

280

τ0=263.2± 2.3ns -43

260

6

β=(3.00± 0.18)*10 cm

Lifetime(ns)

240

220

200

180

160 0

2

4

6

8 20

10 -3

Concentration(10 cm )

12

14

Fig. 8. The concentration dependence of fluorescence intensity of 4D3/2→4I13/2 emission.

8

Intensity(a.u.)

6

4

Ia=9.68± 0.21

2

-21

3

α=(2.87± 0.17)*10 cm -43

6

β=3.00*10 cm

0 0

2

4

6

8 20

10

12

14

-3

Concentration(10 cm )

Abstract A promising new type inorganic scintillation material M′-type Lu1-xNdxTaO4 was

successfully synthesized by solid reaction method. Its structure was determined by Rietveld refinement to the X-ray diffraction data. The calculated density of Lu1-xNdxTaO4 is 9.53-9.67g cm-3, which is the greatest among current inorganic scintillators. Upon light excitation at 355nm, the dominated emissions of Nd3+ were 4

D3/2→4I13/2 and 4D3/2→4I15/2. The concentration dependences of the fluorescence

intensity and fluorescence lifetime of 4D3/2→4I13/2 emission in Lu1-xNdxTaO4 were presented. It was inferred that the optimal doping concentration of Nd3+ was about 5.4% and the fluorescence lifetime of 4D3/2→4I13/2 emission in the zero concentration limit was about 263.1ns. It is suggested to be a potential heavy scintillator due to its high density and fast luminescence decay.

Highlights > M′-type Lu1-xNdxTaO4 was synthesized by solid reaction method. > The dominated emissions of Nd3+ are 4D3/2→4I13/2 and 4I15/2. > The fluorescence lifetime of 4D3/2→4I13/2 emission is about 263.2ns. > The optimal doping concentration of Nd3+ is about 5.4%.