Optical spectroscopy of Eu3+ ions doped in KLu(WO4)2 single crystals

Author’s Accepted Manuscript Optical spectroscopy of Eu3+ions doped in KLu(WO4)2single crystals

T. Koubaa, M. Dammak, M.C. Pujol, M. Aguiló, F. Díaz www.elsevier.com/locate/jlumin

PII: DOI: Reference:

S0022-2313(15)00397-X http://dx.doi.org/10.1016/j.jlumin.2015.07.015 LUMIN13465

To appear in: Journal of Luminescence Received date: 13 March 2015 Revised date: 6 July 2015 Accepted date: 14 July 2015 Cite this article as: T. Koubaa, M. Dammak, M.C. Pujol, M. Aguiló and F. Díaz, Optical spectroscopy of Eu3+ions doped in KLu(WO4)2single crystals, Journal of Luminescence, http://dx.doi.org/10.1016/j.jlumin.2015.07.015 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.

Optical spectroscopy of Eu3+ ions doped in KLu(WO4)2 single crystals T. Koubaa1, M. Dammak1*, M. C. Pujol2, M. Aguiló2, F. Díaz2 1

.Université de Sfax, Faculté des Sciences de Sfax, Département de Physique,

Laboratoire de physique appliquée, groupe de physique des matériaux luminescent, Sfax, Tunisie 2

.FísicaiCristal·lografia de Materials i Nanomaterials (FiCMA-FiCNA)-EMaS. UniversitatRoviraiVirgili (URV), Campus Sesceladesc/ Marcel·lí Domingo, 1, E-43007Tarragona, Spain

Abstract Europium single doped potassium lutetium tungstate Eu3+:KLu(WO4)2 single crystals have been grown with the top seeded solution growth slow cooling method. Their absorption spectra are studied in detail for principal light polarizations, E || Np, Nm and Ng at room and low temperatures. The absorption oscillator strengths parameters are calculated by means of the theory of f–f transition intensities for systems with anomalously strong configuration interactionand by Judd–Ofelttheory. The Ωt (t = 2, 4, 6)intensity parameters, and the {Odk, Ock, Δd, Δc1 and Δc2} (k = 1, 2, 3) ASCI parameters are calculated. The radiative transition rates AR, radiative lifetimes τR, and fluorescent branching ratios βR associated with 5

D0 -7FJ transitions of Eu3+ were determined. The calculated decay times are discussed and compared with

experimental values.

Key Words: Optical spectroscopy, Eu3+ : KLu(WO4)2 , Judd-Ofelt, anomalously strong configuration interaction (ASCI)

*

Corresponding author, E-mail: [email protected]

1

1.

Introduction

The monoclinic Potassium rare-earth double tungstates KRE(WO4)2 (KREW, being RE=Y, Gd and Lu) hosts stand out because they exhibit high absorption and emission cross-sections when doped with active lanthanide ions, partly due to the strong anisotropy of these biaxial crystals [1-10]. They can also be doped with high concentrations of the active ions without substantial fluorescence quenching [1]. The KREW compounds are well-known as solid laser hosts [2- 3]. In particular, the KLu(WO4)2 (KLuW) crystal is very suitable host for Yb and Tm ions [4]. Indeed Yb- and Tm-doped double tungstates (DTs), KRE(WO4)2 proved to be more attractive for intermediate power levels and laser action has been demonstrated in various active ions like Yb: KLuW [5-7] and Tm: KLuW [8-10] using a commercially available diode laser. The excellent results obtained for ytterbium and thulium doped in KLuW lead to study the optical spectroscopy of other rare earth ions in this host, especially europium ion. Further investigations of spectroscopic and laser properties of Eu : KREW is rather interesting. Indeed, Europium ion has been used as a probe ion for studying the chemical surrounding because of its simple energy level structure and because neither the 7F0 ground state nor the 5D0 main emitting state, are degenerated [11, 12]. Furthermore, luminescent materials based on europium ion are very efficient red phosphors which make it an interesting doping ion for materials used in fluorescent lamps, color lighting and optoelectronic devices [13]. Recently, we have reported the optical absorption and emission cross section of Europium doped potassium lutetium tungstate Eu3+:KLuW single crystals [14], however, there is no a complete interpretation of these absorption and emission spectra in order to calculate the Judd-Ofelt parameters. In the present work, we report on Judd-Ofelt (J - O) and anomalously strong configuration interaction (ASCI) theories to investigate the optical properties of Europium doped in KLuW single crystals using the absorption spectra. The different radiative parameters were calculated. These parameters are used to estimate the spontaneous transition probabilities (AR), luminescence branching ratio lifetime

and radiative

.

2. The experimental procedure For the crystal preparation, the precursor oxides K2CO3 (Fluka, 99.9%), WO3 (Fluka, 99.9%), Lu2O3 (Aldrich, 99.9%) and Eu2O3 (Aldrich, 99.9%) were weighted for the desired stoichiometric portions and mixed in a Pt crucible. The solution weight was around 200 g. The Pt crucible was placed inside a vertical tubular furnace at a selected position to create a thermal axial gradient of 0.15 K/mm inside the solution. The solution was homogenized for several hours at around 50 K higher than the expected saturation temperature. The growth occurred as a result of supersaturation when the solution was cooled below the 2

saturation temperature on a parallelipedic seed that was cut parallel to the b crystallographic direction. The optimum cooling rate was 0.1 K/h. The resulting crystals were removed slowly from the solution and cooled slightly above the surface at a rate of 15–25 K/h. The crystal growth temperature and growth rate are similar to those reported in our previous work [14].

3. Optical absorption spectra KLuW belongs to the monoclinic system and space group C2/c, which has the unit cell parameters a=10.576(7)Å ,b=10.214(7)Å , c=7.487(2)Å, =130.68(4)º, Z=4

[15]. KLuW is characterized by

profound anisotropy in its optical properties that makes possible to obtain (Nm, Np and Ng) polarized absorption (and emission) cross sections. Eu3+: KLuW crystal belongs to anisotropy uniaxial crystals. The Eu3+ions are located in C2 symmetry site (substitution of Lu3+) corresponding to only one center for Eu3+ which is verified by the presence of a peak from 7F0→5D0 when light is E//Np [14]. Polarized optical absorption was measured using a Cary Varian 500 spectrophotometer with a resolution of 0.025 nm in the UV–vis region and of 0.2 nm in the NIR region. For low temperature measurements at 6 K, we used an Oxford Instruments Ltd. cryostat (SU 12 model) with helium-gas close-cycle flow. A parallelepipedic prism with dimensions and with faces parallel to a principal optical plane (Ng–Nm plane, Ng–Np plane and Nm–Np plane) was cut and polished from the single crystal, in order to take the polarized measurements. Optical absorption (OA) was measured with polarized light parallel to the three principal optical axes of the KLuW crystal. A detailed description of the crystal structure and of the experiment set up used in this work was reported in our previous work [14]. Optical absorption (OA) was been measured with light polarized parallel to the three principal optical axes Np, Nm and Ng of the KLuW crystal. The detailed structure of polarized optical absorption in KLu0.985Eu0.015(WO4)2 at RT is presented in figure 1. In the UV (350–620 nm) spectral range, the absorption bands are related to transitions from lower-lying 7F0-1 states to 5D0-4, 5L6-7and 5G2-6excited states. The Characteristic bands of Eu3+ ion in the near-IR spanning across 1600–2900nm range are related with transitions to lower-lying 7F5 and 7F6 excited states. The attribution of the different bands (figure 2) is similar to that presented in our previous article with some modification [1]. Indeed, we have reexamined the absorption spectra attribution basing on recently published articles for Eudoped in KY(WO4)2 [16], KGd(WO4)2 crystal [17] and Y3Ga5O12[18]. The absorption spectra are characterized by profound anisotropy that appears both in the absorption peaks intensity, and also in their positions and multiplicities. Indeed, the 7F1 →5D1 absorption bands have a relative intensity at λpeak = 534:3 nm(σabs(m):σabs(p):σabs(g) = 7.1:1.8:0.7 respectively), and it consists of three peaks (centered at 534.3, 539.3 and 540.3 nm) for E // Np, while for E // Nm and Ng the second 3

peak is missing. The different absorption bands for the three polarizations are reported and attributed in table 1.

4. Emission spectra Fig 3 presents the emission spectra at room temperature of Eu : KLuW in the 400 nm – 750 nm spectral range obtained with 298 nm excitation for different Eu3+ concentrations. The spectra consist of three main emissions: first, the weak emission in the vicinity of 590–600 nm is due to the magnetic dipole (MD) transition 5D0→7F1; second, the intense red emission around 610–630 nm is due to the hypersensitive electric dipole (ED) transition 5D0→7F2; and third, another weak emission around 704 nm is due to the 5D0→7F4 transition. The 5D0→7F1 allowed magnetic dipole transition is insensitive to the environment. In the other hand, the 5

D0→7F2 allowed electric dipole transition is very sensitive to the crystal fields around the rare ion. The

ratio (1) of these two transition intensities is given by:

The ratio (1) is a good measure for the Eu3+symmetry site and is related to the Ω2 Judd-Ofelt parameter [19]. When ratio (1) becomes greater, the electric dipole transition is enhanced and quickly increases the crystal field strength. This increase could be related to the covalence or the distortion of the bonds surrounding the active ion. Thus, the ratio (1) serves as a good measure for the symmetry of the Eu3+ site [20, 21]. When the Eu3+ ions occupy low symmetry site with non-inversion centre, the intensity of 5D0→7F2 transition is more prominent than the 5D0→7F1 transition and the ratio (1) intensity is higher than unity. In the case of Eu3+ doped in KLuW host, the ratios (1) intensity determined from the PL spectra excited at 298 nm are equal to 4.36, 2.88 and 1.67 for 1.5, 3 and 5 Europium concentrations respectively. A comparative ratio was reported for the case Eu3+ ion doped in KYbW crystal [22]. The diminution of the I ratio parameter with Europium concentration increasing can be explained by an energy transfer between the Eu3+ ions for high concentrations, because the 5D0→7F2 DE transition is hypersensitive to the crystal field changes.

4

5. Judd-ofelt and ASCI analysis From the experimental measurements of the optical absorption spectroscopy at room temperature, we integrated absorption cross section of the transition from ΦJ initial state to the ΦJ′

can calculate the

final state for each polarization (ΦJ being the 7F0and 7F1 levels) using the following equation:

∑

Where:

∫ The sum is extended to all the peaks included in the absorption band of ΦJ→ ΦJ′ transition and

represents the integrated absorption cross section limited by the ith peak centered at Ei energy. We can also extract the mean energy of each absorption bands (or bands in the case of overlapping Stark manifolds) by :

∑ ∑

(table 1).

The experimental line strengths, of the ΦJ → ΦJ′ transition associated with each polarization is obtained from the experimental spectra by:

′

̅

(

)

Where p relates to Np, Nm or Ng Polarization spectrum, and np is the refractive index 14]. The

meanvalues are averaged over three principal light polarizations:

(

Corresponding theoretical line strength

)

of electric dipole transition between two multiplets is

calculated by the Judd–Ofelt (J-O) theory [23, 24] and by the theory of f–f transition intensities for systems with anomalously strong configuration interaction (ASCI) [25, 26] :

′

∑ Ω |⟨Φ ||

||Φ ′⟩|

5

′

∑ |⟨Φ ||

||Φ ′⟩|

((

Where|⟨Φ ||

|

(

)

)

(

)

)|

||Φ ′⟩| is the square of the reduced matrix elements of the unite matrix U(k),

which is considered to be independent of host matrix and has been calculated by Carnallet al. [27], EJ and EJ’ are the energies of J and J’multiplets, {Ω2, Ω4 and Ω6} are J–O parameters; while {Odk, Ock, Δd, Δc1 and Δc2} refer to ASCI theory (parameter Odk and energy Δd correspond to excited configuration of opposite parity 4fN-15d, while Ock and energies Δc correspond to covalent effects of excited configurations with charge transfer).

In this work, all the absorption bands shown in Fig. 1 and 2 were used to fit the parameters associated with each theory. The root-mean-square deviation between experiment and calculation line strengths is defined by the following equation :

√∑(

) ⁄

Where ‘q’ is the number of transitions used in our analysis and ‘m’ is the number of the parameter for each theory.

The experimental and calculated line strengths Sexp and SJ-O, SACSI respectively, and the energies E(cm-1) of the various absorption bands are listed in Table 2. The root-mean-square deviations (rms) between Sexp and Scal and the relative errors are also listed in this Table 2. The rms values indicate that the fitting results are in good agreement with the experiments. ASCI approximation allows us to obtain lower root-mean-square (rms = 0.3) deviation between experimental and calculated line strengths values then that obtained for judd-ofelt theory (rms = 0.7). Although the rms values are close, we can conclude that ASCI theory used for the Eu: KLuW gives more consistent results than the Judd-Ofelt theory. The set of corresponding modeling parameters, namely {Ω2, Ω4 and Ω6} for J–O theory and {Odk, Ock, Δd, Δc1 and Δc2} for ASCI theory, is summarized in this table 3. The calculated values of the ASCI parameters are in good agreement with those obtained for Eu3+ ions in KYW [16] and KGdW [17] crystals.

6

Furthermore, the calculated Ω2 and Ω4 J-O parameters are in agreement with those calculated for Eu3+: Gd2WO6 and Eu3+: Gd2(WO4)3nanophosphors (table 4) [28]. Judd–Ofelt intensity parameters reflect local structure and bonding in the vicinity of RE ions. In particular, Ω2 exhibits the dependence on the covalence between RE ions and ligand anions and gives information

about the asymmetry of the local environment of Eu3+ site [29]. The host system presenting larger Ω2 values (Ω2> Ω4), which is the case of KLuW: Eu, induces a more polarizable chemical environment and has stronger covalent character of the metal-donor interactions. This result has been proved for the case of Tm3+ ions doped in TeO2-WO3 glass [30].

6. Radiative life time and experimental life time Fig 4 presents the luminescence decay of the 5D0→7F2 transition for different Eu3+concentrations. We note that for low Europium concentrations (1 at. % and 1.5at. %), the decay time can be fitted with a simple exponential decay; however for higher Eu3+ concentrations the simple decay cannot fit correctly the curves. Indeed, when there is no interaction between rare earth ions, the decay curve is usually a single exponential function. This result confirms the presence of an energy transfer between Eu3+ ions for high Europium concentrations. The observed lifetime of 5D0 multiplet can be approximately regarded as the radiative lifetime assuming that the nonradiative multi-phonon transition rate from 5D0 is negligibly small. It is reasonable since the large energy gap (17200 cm-1) between 5D0 and its next low-lying 7F0 requires the participation of at least 18 lattice phonons to bridge it (the highest phonon energy in the crystal structure is around 900 cm-1) [14]. The spontaneous emission probabilities A (J,J’) from an excited manifold J ’to a lower manifold J can be calculated by: ′

′

′

Where Aed and Amd are the electric-dipolar and magnetic-dipolar contributions, respectively.

′

′

̅

′

̅

′

7

Where J=0 represents the total angular momentum of

5

D0, n the mean refractive index

(n= [(np2+nm2+ng2)/3]1/2) [14] of the host and Sed and Smd are the electric and magnetic dipole line strengths respectively. Similarly, absorption line strengths Sed were also determined for excited-state absorption channels from metastable 5D0 state (see Table 2).The magnetic-dipolar transition length strength Smd is given by the standard formula:

′

||Φ′ ′ ⟩|

|⟨Φ ||

For 5D0→7F1, J′=J+1, the magnetic-dipole Smd can be expressed as :

′

h

*

+

Where, m is the electron mass and c is the light velocity [31]. The fluorescence branching ratio of each of the transitions and the radiative lifetime of 5D0 can be determined from the spontaneous transition probability according to these equations ′

′ ∑′ ∑′

′ ′

The calculated spontaneous transition probabilities of electric-dipole transition Aed, the magnetic-dipole transition Amd, the total spontaneous transition probabilities AR, the fluorescence branching ratios βR as well as the radiative lifetimes τR are determined using the Judd-Ofeltand ASCI are reported in Table 5. The 5D0→7F2 (590–600 nm) emission gives by far the most intense band, in qualitative agreement with the results of the J–O analysis and ASCI theory which are presented in Table 2. The results (βR >85%) show that the emission transition of Eu3+:KLuW crystal is very intensive and will hopefully realize light output. The fluorescence lifetime of the 5D0 manifold can be estimated to be 0.67 ms for 1.5 at. % Eu doped in KLuW, and the radiative lifetime τR of the same level is calculated to be 0.99 ms (ASCI), the difference

8

between the experimental and the calculated values can be due to non-radiative decay from the 5D0 state of Eu3+. So the luminescent quantum efficiency of the 5D0 level ηQE =

=

is 67.7% (ASCI).

The high value of quantum efficiency of the 5D0 level confirming that the multiphonon relaxation is inefficient [32], as expected in our previous work [14] and the contribution of other non-radiative phenomena is low, which promotes the KLuW crystal as a good material for optoelectronic applications.

Conclusions Absorption, luminescence and decay time of Europium doped in potassium lutetium double tungstate Eu3+:KLu(WO4)2 single crystals have analyzed at room temperature. Absorption spectra are determined for this crystal with respect to principal light polarizations, E||Np, Nm and Ng. Spectroscopic properties of Eu:KLuW are modeled within conventional Judd–Ofelt theory, in addition to theory of f–f transition intensities for systems with anomalously strong configuration interaction (ASCI), yielding absorption oscillator strengths, luminescence branching ratios and radiative lifetime of 5D0 metastable state.The comparison between the calculated and the experimental decay times of the 5D0multiplet shows the contribution of a non radiative processes and an energy transfer between the Eu3+ions. The 5D0 luminescence decay curve exhibited single exponential with a decay time of 0.67 ms. The emission quantum efficiency of the 5D0 level of Eu3+ ion in KLuW is 67.7 % under 298 nm excitation. On the basis of these radiative parameters characteristic, it is suggested that the Eu3+:KLuW is a potential host material for optical applications.

Acknowledgments This work was supported by the Spanish Government under project MAT2013-47395-C4-4-R and by the Generalitat de Catalunya under project 2014SGR1358. F.D. acknowledges additional support through the ICREA academia award for excellence in research.

9

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[21]A. Patra, E. Sominska, S. Ramesh, Y. Koltypin, Z. Zhong, H. Minti, R. Reisfeld,A. Gedanken, J. Phys. Chem. B. 103 (1999) 3361. [22] M.H. Bartl, K. Gatterer, E. Cavalli, A. Speghini, M. Bettinelli, Spectrochim. Acta, Part A. 57 (2001) 1981. [23]B.R. Judd, Phys. Rev. 127 (1963) 750. [24] G.S. Ofelt, J. Chem. Phys. 37 (1962) 511. [25] E. B. Dunina, A. A. Kornienko, L.A. Fomicheva, Cent. Eur. J. Phys. 6 (2008) 407. [26] P.A. Loiko, A.S. Yasukevich, A.E. Gulevich, M.P. Demesh, M.B. Kosmyna, B.P. Nazarenko, V.M. Puzikov, A.N. Shekhovtsov, A.A. Kornienko, E.B. Dunina, N.V. Kuleshov, K.V. Yumashev, J. Lumin. 137 (2013) 252. [27] W.T. Carnall, J. Chem. Phys. 49 (1968) 4424. [28] Q. Zhang, Qi. Meng, Y. Tian, X. Feng, J. Sun, S. LÜ, Journal of Rare Earths. 29(9) (2011) 815. [29] C. K. Jorgensen, R. Reisfeld, J. Less-Common Met. 93 (1983) 107. [30] G. Özen, A. Aydinli, S. Cenk, A. Sennarglu, J. Lumin. 101 (2003) 293. [31]W. T. Carnall, P. R. Fields, B.G. Wybourne, J. Chem. Phys. 42 (1965),3797. [32] Y.Wei, C. Tu, H.Wang, F.Yang, G. Jia, Z.You, X.Lu, J.Li, Z.Zhu, Y.Wang, J.Alloys and Compounds.438 (2007) 310.

11

Transition

Np

E (cm-1)

Ei -1

(cm ) 7

7

F1→7F5 F0→7F5

3514

F1→7F6

4608

7

F0→5F6

4888

7

F1→5D0

7

F0→5D0

17205

7

F1→5D1

18633

F0→5D1

18953

F0→5D2

21463

7

7

7

F1→5D3

3511,3

10

3885,3

14

F0→5D3

4606

6.8

4883

12.4

F1→5L6

6.8 12.4

Ei -1

(cm )

Ng

Γi (cm2) Γ (cm2)

3518

4.6

3892,7

14.2

3939.7

7.65

4019

3.8

4610

10

4876

90

5174

5

16945

0.6

18508

6.3

18716

12.3

4.6

Ei -1

(cm )

Γi (cm2) Γ (cm2)

3515.5

12

4862

10

95

18716

1.4

18535

6.54

18717

3.56

18940

1.06

18939

1.22

18940

1.18

18976

0.48

18976

0.62

18976

0.7

21426

1.76

21426

27.1

21426

4.4

21457

24.37

21491

35

21492

4.03

23842

2.65

23878

3.6

24014

5.2

24078

9.6

24089

2.43

24314

0.8

24337

0.5

24806

3.3

24806

3.3

24874

9.58

24971

2.4

24968

4

24998

1.08

25056

2.15

25115

2.17

25106

2

23990 5.7

24323 4.18

24962

22.24 25043

18.06

10

0.6

0.44 10.1

12

10

17205

24837

7

10

14

24058 7

Γi (cm2) Γ (cm2)

3925

7

Nm

18.6

20.68

1.4

9.9

Table 1:

12

Table 1 continued

7

F0→5L6

25311 25313

88.6

25321 125.2

25871 19.27

25868 11.54 25909

7

F1→5L7

26024 26016

4.37

25293 71.8

2.4

45.08 26042 16.46 49.64

26135 21.44

26121

9.28

26175

9.96

26219 14.48 7

F0→5G2-6

26441

5.7

26445 26461 18.56 25.56 26491

10.1

26733 7

F0 –5L8 27507

7

7

F0 –5D4

27539

27582

6

2

26662

3

26709

2.2

27253

9.18

26228

4

35.48 26491

4

8

27498 15.76 8

27525

12.4

27586

5.5

27618

6.9

40.56

27572

4

4

Table 1: The energy values of the electronic transitions corresponding to the absorption bands of Eu : KLuW and their integrated absorption cross sections, obtained from room temperature absorption spectra (fig 1 and 2).

13

Transition

Energy (cm-1)

Sexp (10-22 cm2)

SJ-O (10-22 cm2)

Sacsi (10-22 cm2)

7

F1→7F5

3514

4.09

4.09

4.09

7

F0→7F6

4888

4.29

4.60

4.37

7

F1→5D1

18633

1.14

1.28

1.13

7

F0→5D2

21463

0.72

0.39

0.64

7

F1→5D3

23990

0.55

0.22

0.65

7

F1→5L6

24962

0.93

0.29

0.89

7

F0→5L6

25311

1.71

0.48

1.50

7

F1→5L7

26024

1.67

0.58

1.66

F0→5G2-6

26445

0.35

0.43

0.48

F0→5D4

27539

0.25

0.02

0.10

0.7

0.3

7

7

rms (10-22 cm2)

Table 2: experimental and calculated oscillator strength calculated by Judd-Ofelt and ASCI theories obtained for the different absorption bands of Eu: KLuW.

14

Eu3+:KLu(WO4)2

Od2(1)

Od4(1)

Od6(1)

Oc2(1)

Oc4(1)

Oc6(1)

Δd(2)

Δc1(2)

Δc2(2)

Ref

1.75

0.426

0.51

0.093

0.002

0.003

38979

18892

26207

This work

3+

Eu :KY(WO4)2

3.2

3.0

1.7

-0.06

37,000

18,600

26,500

[15]

Eu3+:KGd(WO4)2

2.6

2.3

0.76

-0.014 -0.024 -0.015 42 360

18 790

26 590

[16]

(1)

[10-10 cm2]

(2)

[cm-1]

0.08

-0.08

Table 3: Calculated {Odk, Ock, Δd, Δc1 and Δc2} ASCI parameters obtained for Eu : KLuW in comparison with those obtained for KGdW and KYW crystals.

15

Compounds

[Eu](mol %)

Ω2 (10-20cm2)

Ω4 (10-20cm2)

Ω6 (10-20cm2)

Ref.

Eu: Gd2(WO4)3

1-5

5.47-5.86

0.22-0.21

-

[28]

Eu: Gd2WO6

1-5

4.27-4.32

0.19-0.20

-

[28]

Eu: KLu(WO4)2

1.5

4.9

0.2

0.32

This work

Table 4: calculated Ω2 and Ω4 parameters calculated for different hosts containing WO-n fragment ions.

16

 (nm)

Aed -1

(s )

Amd

AR

-1

-1

(s )

(s )

BR

τR (ms)

Aed

AR

-1

-1

(s )

(s )

Judd-Ofelt D0→ F4

705

8.34

0

D0→ F2

618

441.35

0

D0→7F1

595

0

68.4

5 5

7

5

7

BR

τR

τexp

(ms)

(ms)

ASCI 8.34

0.016

16.7

16.7

0.017

441.35 0.852 1.93 925.3 925.3 0.916 0.99 68.4

0.132

-

-

0.67

0.068

Table 5: The calculated Aed, Amd, AR, βR and τR parameters using Judd-Ofelt and ASCI theories.

17

Figure captions

Fig. 1. Room temperature optical absorption of 1.5 at.% Eu: KLuW. Fig. 2. Absorption spectrum of 1.5 at % Eu : KLuW crystal (light polarization is E|| Nm). Fig.3. Room temperature emission spectra of KLuW doped with different Europium concentrations. Fig. 4. Room temperature decay curves of KLuW single crystals doped with different Europium concentrations.

18

0,8

3 7 7

2

F1

7

F5

7

1

cross section 10

-20

cm

2

0

3,5

7

F0

7

F0

F6

0,6

F5 4,5

5,0

5,5

D1 7

0,0 18,0 2,0

6

1,5

F0

5

D2

5

F1

D1

18,5

7

F0

5

19,0

19,5

28,0

28,5

D4

1,0 0,5

2

0,0 22,0 27,0

0 21,0

21,5

1,0 7

0,8

F0

E//Ng E//Nm E//Np

0,2

8

4

5

0,4

4,0

7

7

F1

5

7

L7

F0

5

10 7

G2-6

8

0,6

6

0,4

4

0,2

2

0,0 25,5

26,0

26,5

27,5

27,0

0

7

F1

24,8

5

F0

5

L6

L6

25,0

25,2

25,4

0,2 0,6

7

F1

5

7

D3

0,4

F0

5

D0

0,1

0,2 0,0

0,0 23,6

23,8

24,0

24,2

16,5 3

17,0

17,5

-1

Energy [10 cm ]

Fig. 1.

19

100

E//Nm 7

F0

5

7

D2

F0

5

L6

7

5

7

5

7

5

(1) F1

2

cross section  [x10 cm ]

80

(2) F1

60

-21

7

F0

7

L7

F6

G2-6

(3) F0

L8

20 7 7 7

10

7

F0,1

7

F5 7

F1

5

F0,1

5

D1

F1

5

L6

F1

5

D4

2 1

D0

3

0 7

2

4

6

F0,1

20

5

D3 25

3

30

-1

Energie [10 cm ]

Fig. 2.

20

F2

D0

5

5

D0

5

7

D0

F3

7

7

F0

F4

5

D0

5

D0

7

F1

7

Intensity [arb.units]

1.5 % at. Eu:KLuW 3% at. Eu:KLuW 5% at. Eu:KLuW

500

550

600

650

700

750

wavelength [nm] Fig. 3.

21

0,004

at1.5.Eu

at1.Eu

0,006

0,004 0,002

0,002 0,001

0,000

0,000

0

2 0

4 4

0

8

at3.Eu

0,005

Intensity [arb.units]

Intensity [arb.units]

0,003

0,004

0,003

0,003

0,002

0,002

0,001

0,001

0,000

0,000

4

0,004

0,005

0,004

0

2

0,000

8

at5.Eu

0

time [ms]

4 0,008

4

8

time [ms]

Fig. 4.

22

Highlights 

Absorption spectra of Eu: KLuW are investigated with respect to principal light polarizations, E||Np, Nm and Ng.



Spectroscopic properties of Eu:KLuW are modeled within conventional Judd–Ofelt theory and with anomalously strong configuration interaction (ASCI).



the 5D0 multiplet shows the contribution of a non radiative processes and an energy transfer between the Eu3+ ions.



It is suggested that the Eu3+ : KLuW is a potential host material for optical applications.

23