Growth and spectroscopic characterization of Tm3+:Ca10Li(VO4)7 crystal-a potential crystalline medium for 2 µm lasers

Journal of Crystal Growth 520 (2019) 62–67

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Growth and spectroscopic characterization of Tm3+:Ca10Li(VO4)7 crystal-a potential crystalline medium for 2 µm lasers Guojiao Liua,b, Zhiyong Baia,b, Feifei Yuana, Yisheng Huanga, Lizhen Zhanga, Zhoubin Lina,

T

⁎

a Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China b University of Chinese Academy of Science, Beijing 100049, China

A R T I C LE I N FO

A B S T R A C T

Communicated by Satoshi Uda

The single crystal Tm3+:Ca10Li(VO4)7 with dimensions of Ø 23 × 25 mm3 was grown by Czochralski method. It’s thermal and spectroscopic properties were investigated. The thermal expansion coefficient αa is 1.671 × 10−5 K−1 and αc is 1.462 × 10−5 K−1. The absorption cross-sections at 794 nm are 2.43 × 10−20 cm2 and 1.04 × 10−20 cm2 for π- and σ- polarization, respectively. The largest stimulated emission cross-section corresponding to the 3F4 → 3H6 transition of Tm3+ ions, is 1.92 × 10−20 cm2 at 1883 nm for π- polarization and 1.69 × 10−20 cm2 at 1917 nm for σ- polarization. The fluorescence lifetime is 1.05 ms. The broad and smooth gain profile from 1750 nm to 2010 nm means that Tm3+:Ca10Li(VO4)7 is a potential laser crystal for tunable and ultrashort pulse lasers near 2 µm.

Keywords: A1. Characterization A2. Single crystal growth A2. Czochralski method B3. Solid state laser

1. Introduction There has been continuous interest in developing solid-state 2 μm lasers, for their applications in plenty of fields: surgery, laser radar, remote sensing, atmosphere monitoring and so on, due to their eye-safe emission at about 2 µm matches the absorption of water molecules in bio-tissues, and several absorption lines of chemical compounds (H2O, CO2, etc.) present in the atmosphere. Among the most promising laser materials in 2 μm spectral region, Tm3+-doped laser crystals reveal a number of attractive advantages, such as the availability of commercial AlGaAs laser diode (LD) pumping (3H6 → 3H4 transition ∼800 nm), the high quantum efficiency associated with the cross relaxation process, and wide laser wavelength tuning around 2 μm. So far, many Tm3+doped oxide laser crystals, e.g. Y3Al5O12 [1], YVO4 [2], GdVO4 [3], LuVO4 [4], and Ca3(VO4)2 [5] etc. have been investigated, and laser operation at about 2 μm have been realized. Vanadate crystals usually have good physicochemical properties, and are ideal candidate materials for laser matrix, a well-known example is the family of REVO4 (RE = Y, Gd or Lu) crystals [6]. In order to obtain high efficient 2 μm laser output, a host with low phonon energy is more appreciated, which is helpful to reduce nonradiation relaxation. Vanadates have a lower phonon energy of all oxide materials, this gives them an advantage in the choice of Tm3+-doped host materials. Recently, the trigonal vanadates with formula Ca9X(VO4)7 (where X ⁎

is La, Y, Gd, Lu, and Bi) have captured the attention of researchers, for their nonlinear properties for second-harmonic generation, such as Ca9Bi(VO4) [4], Ca9Y(VO4)7 [5] and Ca9La(VO4)7 [6]. Due to their partially disordered whitlockite-related structure, easy to grow the single crystals, they are also being studied as potential laser crystals. Many of the Ln3+ ions doped Ca9X(VO4)7 crystals were grown, and their spectroscopic properties were studied thoroughly [6–11]. However, as there exist scattering centers in the crystals, which are difficult to be eliminated by annealing, there are no reports of laser output from these crystals so far. To solve the aforementioned problem, an interesting attempt of modifying these whitlockite-type vanadates is entering Li or K ions, which leads to the formation of Ca10(Li/K)(VO4)7 crystals, Li or K ions’ substitution will fill the vacant crystallographic positions, and result in the absence of scattering centers or markedly reducing their concentration in the crystals [12]. Up to now, Yb3+ or Nd3+-doped Ca10(Li/K)(VO4)7 crystals with high quality were grown successfully, their spectroscopic and thermal properties were investigated [13,14], especially, the laser oscillations of Nd3+-doped Ca10Li(VO4)7 crystal was demonstrated under flash lamp pumping, the experimental results are satisfaction [13,14]. Here, we report the crystal growth, thermal and spectroscopic study of Tm:Ca10Li(VO4)7 crystal.

Corresponding author. E-mail address: [email protected] (Z. Lin).

https://doi.org/10.1016/j.jcrysgro.2019.05.025 Received 9 April 2019; Received in revised form 15 May 2019; Accepted 20 May 2019 Available online 21 May 2019 0022-0248/ © 2019 Elsevier B.V. All rights reserved.

Journal of Crystal Growth 520 (2019) 62–67

G. Liu, et al.

2. Experimental details The Tm3+:Ca10Li(VO4)7 single crystal was grown by the Czochralski method, for Ca10Li(VO4)7 compound melts congruently at about 1500 °C. The raw materials for crystal growth were synthesized by solid station reaction, the chemicals CaCO3 (99.99%), Li2CO3 (99.99%), Tm2O3 (99.99%) and V2O5 (99.99%) powders in a stoichiometric ratio were used, in which the Tm3+ doping concentration was set at 6 at.%. The mixtures were ground and mixed in an agate mortar for blending evenly, and extruded to pellets. Then, the pellets were placed into an alumina crucible and sintered at 1000 °C for 48 h in a muffle furnace. These processes were repeated, and the sintering temperature was raised to 1300 °C. After that, the formation of Tm3+:Ca10Li(VO4)7 phase was confirmed by X-ray powder diffraction (XRD). The single crystal of Tm3+:Ca10Li(VO4)7 was grown in a Ø 45 mm × 50 mm iridium crucible, in a 25 KHz mid-frequency induction furnace (DJL-400) filled with nitrogen atmosphere. The pulling rate was 1–1.5 mm/h, and the rotation rate was 5–20 rpm, a [0 0 1] oriented Ca10Li(VO4)7 crystal was used as a seed. The growth process lasted about 30 h, then the grown crystal was pulled slowly out of the melt, and cooled to room temperature at a rate of 15–30 °C/h. In order to eliminate the color centers, and to reduce the thermal stress, after the crystal was removed from the growth furnace, it was annealed at 1100 °C for 24 h in the air in a muffle furnace. The XRD data of the grown crystal were collected in the range of 10–80 ° with a scan speed of 5°/min and a step of 0.02°, by using an Xray diffractometer (Rigaku, Miniflex 600) equipped with CuKα radiation at room temperature. The concentration of Tm3+ ions in the grown Tm3+:Ca10Li(VO4)7 crystal was measured by Inductively Coupled Plasma OES spectrometer (HORIBA Jobin Yvon, Ultima 2). Two polished rectangular crystal samples with dimensions of 5 × 5 × 10 mm3 along a- and c- axis were used to acquire the thermal expansion coefficients respectively, which were measured by a thermal dilatometer (DIL 402PC) in the range of 25 °C to 500 °C at a heating rate of 5 °C/min. The polarized absorption spectra were measured by a Perkin Elmer UV–VIS-NIR spectrophotometer (Lambda 950) with the polarized incident light parallel (π- polarization) and perpendicular (σpolarization) to the optic c- axis. The fluorescence spectra and fluorescence lifetime were measured by Edinburgh Instruments (FSL920 and FSL980) with a xenon lamp and an OPO laser as exciting sources, respectively. In order to avoid the effects of radiation trapping and total internal reflection, a powder sample was used for the measurement of the fluorescence lifetime. All the measurements were performed at room temperature.

Fig. 1. XRD diffraction pattern of Tm3+:Ca10Li(VO4)7 crystal.

Fig. 2. The grown Tm3+:Ca10Li(VO4)7 crystal.

3. Results and discussion 3.1. Crystal growth The XRD pattern of the grown Tm3+:Ca10Li(VO4)7 crystal is shown in Fig. 1, the XRD pattern of Ca10K(VO4)7 (PDF#85-0280) is used for comparison, for the lack of structural data of Ca10Li(VO4)7, as Ca10Li (VO4)7 is isostructural to Ca10K(VO4)7 [14]. The diffraction peaks match well the standard pattern of the Ca10K(VO4)7, indicating that a pure Tm3+:Ca10Li(VO4)7 phase without any parasitic phase is obtained. The photo of the grown Tm3+:Ca10Li(VO4)7 crystal with dimensions of Ø 23 × 25 mm3 is shown in Fig. 2, the insets are the wafers before (a) and after (b) annealing in the air. The coloration of the as-grown crystal is green, which is due to the reduction of the V5+ ions to V4+ and V3+ ions, and the appearance of oxygen vacancies. After annealing in the air, the coloration changed to yellowish, this improved the transparency of the crystal. The concentration of Tm3+ ions in Tm3+:Ca10Li(VO4)7 crystal was measured to be 10.24 at.% (1.639 × 1020 ions/cm3) by ICP-OES, consequently, the segregation coefficient of Tm3+ in the crystal is 1.7, which means that Tm3+ ions can be easily doped into the Ca10Li(VO4)7

Fig. 3. The thermal expansion curves of Tm3+:Ca10Li(VO4)7 crystal.

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Fig. 4. (a) The polarized absorption spectra of Tm3+:Ca10Li(VO4)7 crystal. (b) absorption cross-sections σabs for the 3H6 → 3H4 transition of Tm3+ ion. Table 1 Measured and calculated line strengths for Tm3+:Ca10Li(VO4)7 crystal. σ-polarization

Excited state

3

F4 H5 3 H4 3 F2,3 1 G4 3

π-polarization

λ¯ (nm)

Sexp (10

1749 1204 785.4 689.7 471

1.097 0.8398 1.282 3.002 2.221

−20

−20

2

cm )

Scal (10

2

cm )

0.6966 0.5627 1.594 2.736 1.921

λ¯ (nm)

Sexp (10−20cm2)

Scal (10−20cm2)

1755 1205 792.8 686.8 470.8

0.9307 0.6321 2.718 2.594 1.839

0.8859 0.4402 2.598 2.473 2.167

Ω2 = 7.30 × 10−20 cm2, Ω4 = 2.07 × 10−20 cm2, Ω6 = 1.15 × 10−20 cm2

Table 2 Calculated radiative transition rates, fluorescence branching ratios and radiative lifetimes of Tm3+: Ca10Li(VO4)7 crystal. Transition

λ¯ (nm)

π-polarization A(J → J') (s

−1

)

σ-polarization Atotal (s

−1

)

β (%)

A(J → J') (s

−1

)

τrad (ms) Atotal (s

−1

)

β (%)

F4 → H 6

1725

448.62

448.62

100

536.45

536.45

100

1.86

3

H 5 → 3 F4 3 H6

4226 1225

13.35 550.16

563.51

2.37 97.63

10.13 468.14

478.28

2.12 97.88

2.09

H4 → 3H5 F4 3 H6

2166 1432 784

67.05 237.90 2450.27

2755.21

2.43 8.63 88.93

56.97 256.12 2544.49

2857.58

1.99 8.96 89.04

0.35

F3 → 3H4 H5 3 F4 3 H6

5552 1558 1138 686

6.45 650.19 191.63 4135.67

4983.93

0.13 13.05 3.85 82.98

5.76 907.91 130.70 2448.84

3493.21

0.16 25.99 3.741 70.10

0.29

F2 → 3F3 H4 3 H5 3 F4 3 H6

17,513 4215 1431 1069 670

0.054 26.37 490.31 1220.74 1254.11

2991.58

0.002 0.88 16.39 40.81 41.92

0.049 32.66 300.14 1762.89 616.35

2712.09

0.0018 1.20 11.07 65.00 22.73

0.37

G4 → 3F2 F3 3 H4 3 H5 3 F4 3 H6

1634 1494 1177 763 646 470

29.33 107.62 456.20 1554.04 338.88 2025.03

4511.09

0.65 2.39 10.11 34.45 7.51 44.89

23.63 69.42 487.88 1262.76 228.37 2429.64

4501.70

0.52 1.54 10.84 28.05 5.07 53.97

0.22

3

3

3 3

3 3

3 3

1 3

expansion curves of the Tm3+:Ca10Li(VO4)7 crystal are shown in Fig. 3. The average linear thermal expansion coefficients of Tm3+:Ca10Li (VO4)7 crystal, calculated from the slopes of the expansion curves, are αa = 1.671 × 10−5 K−1 and αc = 1.462 × 10−5 K−1. The αa/αc is 1.14, which means that anisotropy of the thermal expansion is small, this is favorable for crystal growth and laser applications. According to the

host. 3.2. Thermal properties Thermal expansion coefficient is one of the most critical thermal factors for growth and applications of laser crystals. The thermal 64

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oscillator which causes the thermal expansion of crystal. The small anisotropic thermal expansion means that the atoms’ vibrations and thermal stress are more uniform in all directions of the crystal during the process of growth, annealing, and applications, which are helpful to prevent crystal cracking [15,16]. There is a kick at around 300 °C, which probably caused by the instability of the test condition such as the shake of the sample or the temperature fluctuations. 3.3. Spectroscopic properties The polarized absorption spectra of Tm3+:Ca10Li(VO4)7 crystal in the range of 300–2100 nm at room temperature are shown in Fig. 4(a), the absorption band related to the 3H6 → 3H4 transition of Tm3+ ions is enlarged and shown in Fig. 4(b). The spectra show obvious polarization anisotropy, the absorption bands observed at about 475, 690, 794, 1210 and 1701 nm correspond to the transitions of Tm3+ ions from ground state 3H6 to the excited states of 1G4, 3F2,3, 3H4, 3H5 and 3F4, respectively. For the absorption band at around 795 nm, the maximum absorption cross-section is 2.43 × 10−20 cm2 for σ- polarization with the full-width at half-maximum (FWHM) of 7.5 nm, and 1.04 × 10−20 cm2 for π- polarization with the FWHM of 34 nm. Such a broad and strong absorption band at around 800 nm is suitable for the widely used AlGaAs LD pumping. The UV absorption edge of Tm3+:Ca10Li(VO4)7 crystal is at about 325 nm (Eg = 3.82 eV). Judd-Ofelt (J-O) theory is widely accepted to obtain the spectral parameters of the rare earth elements in laser materials [17,18]. According to the theory, the absorption spectra are used to calculate the oscillator strength parameters Ω, fluorescence branching ration β, radiative lifetime τrad and transition probability A. The results are listed in Table 1, 2. Basically, the intensity of electric dipole transitions are far stronger than those of magnetic dipole transitions, they make more contribution to the line strengths, as a result, the magnetic dipole transitions are neglected in the calculation. The polarized fluorescence spectra of the Tm3+:Ca10Li(VO4)7 crystal excited at 790 nm are shown in Fig. 5, the broad band spanning from 1750 to 2050 nm is due to the 3F4 → 3H6 transition. The emission band with peak at about 1900 nm has a FWHM of 136 nm for π- polarization, and 195 nm for σ- polarization, respectively. The fluorescence decay curve of the 3F4 upper laser level of Tm3+ ions is shown in Fig. 6, the fluorescence lifetime is 1.05 ms. It is much shorter than the radiative lifetime (1.86 ms), this phenomenon also appears in other Tm3+-doped crystals: Tm3+:Ca9La(VO4)7 [11], Tm3+:(Sc0.5Y0.5)2SiO5 [19] and Tm3+:SrMoO4 [20]. The main cause of the short fluorescence lifetime is attributed to the non-radiative relaxation processes, which are probably related to the color centers. Even annealing in the air, the color centers may not wholly eliminated. The fluorescence quantum efficiency η = τf/τr was calculated to be 56.5%. The stimulated emission cross-section of excited state 3F4 to the ground state 3H6 was calculated by Füchtbauer–Ladenburg (F-L) formula:

Fig. 5. The polarized fluorescence spectra of Tm3+: Ca10Li(VO4)7 crystal excited at 790 nm.

Fig. 6. The fluorescence decay curve of Tm3+:Ca10Li(VO4)7 crystal.

σse =

λ5β I (λ ) 8πn2cτrad ∫ λI (λ ) dλ

(1)

where β is the branching ratio, τrad is the radiative lifetime, n is the refractive index (n = 1.82 for Tm3+:Ca10Li(VO4)7 crystal), c is the speed of light, and I(λ) is the relative fluorescence intensity in different wavelength λ. The stimulated emission cross-section at 1918 nm was calculated to be 1.69 × 10−20 cm2 for σ- polarization, and 1.92 × 10−20 cm2 at 1885 nm for π- polarization, as shown in Fig. 7. The FWHMs of the emission band are 160 and 151 nm for π- and σpolarizations, respectively. The gain cross section σg(λ) is an important parameter for laser materials, it can be calculated by absorption and emission cross-sections according to the following equation:

Fig. 7. Polarization stimulated emission spectra for the 3F4 → 3H6 transition of Tm3+:Ca10Li(VO4)7 crystal.

crystal lattice vibration dynamics, the atoms are vibrating around the lattice equilibrium position, and this vibration is not harmonic

σg (λ ) = pσse (λ ) − (1 − p) σabs (λ ) 65

(2)

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G. Liu, et al.

Fig. 8. Gain cross-sections for the 3F4 → 3H6 transition of Tm3+:Ca10Li(VO4)7 crystal for π- (a) and σ- (b) polarizations.

coefficients αa and αc are 1.671 × 10−5 K−1 and 1.462 × 10−5 K−1, respectively, showing a weak anisotropic, which is helpful for crystal growth and laser applications. There is a broad and strong absorption band at around 795 nm, which is suitable for the AlGaAs LD pumping. The largest stimulated emission cross-section corresponding to the 3 F4 → 3H6 transition is 1.92 × 10−20 cm2 at 1883 nm for π- polarization with a FWHM of 160 nm. The fluorescence lifetime is 1.05 ms. The Judd-Ofelt analysis yielded intensity parameters of Ω2 = 7.3, Ω4 = 2.07 and Ω6 = 1.15. The spectroscopic properties of Tm3+:Ca10Li (VO4)7 are very promising for broadly tunable and ultrashort pulse lasers near 2 µm.

Table 3 Comparison of spectral parameters of Tm3+:Ca10Li(VO4)7 and other Tm3+doped crystals. Crystals

YVO4

Ca9La (VO4)7

GdVO4

Ca3 (VO4)2

Ca10Li (VO4)7

Nc (at.%) λp (nm)

5 797.5 5

6 799.2 (π) 797.9 (σ) –

0.26 795

FWHM at λp (nm) σabs at λp (10−20 cm2) λext (nm)

2.5

FWHM at λext (nm)

100

5.72 793(π) 791.3(σ) 19.1(π) 8.2(σ) 0.42(π) 1.5(σ) 1858(π) 1858(σ) 173.34

σse at λext (10−20 cm2) τf (ms) References

1.6

10.22 794(π) 794(σ) 7.5(π) 34(σ) 2.43(π) 1.04(σ) 1885(π) 1907(σ) 136(π) 195(σ) 1.427(π) 1.21(σ) 1.05 This work

1800

0.047 [2]

0.38(π) 1.28(σ) 1.19 [11]

40 –

4.03(π) 2.46 (σ) 1830

1970

–

20

–

–

2.5 [22]

– [23]

Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 61775217), the National Key Research and Development Program of China (No. 2016YFB0701002), and the Natural Science Foundation of Fujian Province (No. 2018J01109). References

where p is the population inversion ratio of the Tm3+ ions, p = N2/NTm, N2 is the number of Tm3+ ions at 3F4 energy level, NTm is the total number of Tm3+ ions in the crystal. The gain cross-sections of 3F4 → 3 H6 transition for different p values ranging from 0.1 to 0.5 are presented in Fig. 8. The wavelength ranging from 1750 nm to 2010 nm is observed for p = 0.3, the maximal gain cross-sections are 0.45 × 10−20 cm2 and 0.54 × 10−20 cm2 for π- polarization and σpolarization, respectively, which are higher than 0.12 × 10−20 cm2 reported for Tm3+:GdVO4 [21]. The broad gain curves show the possibility of Tm3+:Ca10Li(VO4)7 as a tunable laser crystal. The spectral parameters of Tm3+:Ca10Li(VO4)7 crystal and some matured Tm3+-doped vanadates laser crystals are listed in Table 3. It can be seen that Tm3+:Ca10Li(VO4)7 crystal also possesses large FWHMs of the absorption and emission bands, big emission cross section and long fluorescence lifetime, all of them are comparable with these of the other Tm3+-doped vanadates crystals. Thus, one can conclude that Tm3+:Ca10Li(VO4)7 crystal is a promising laser crystal for 2.0 μm lasers.

[1] P.X. Song, Z.W. Zhao, X.D. Xu, B.X. Jang, P.Z. Deng, J. Xu, Growth and properties of Tm: YAG crystals, J. Cryst. Growth 270 (2004) 433–437. [2] K. Ohta, H. Saito, M. Obara, Spectroscopic characterization of Tm3+: YVO4 crystal as an efficient diode pumped laser source near 2000 nm, J. Appl. Phys. 73 (1993) 3149–3152. [3] V.A. Mikhailov, Y.D. Zavartsev, A.I. Zagumennyi, V.G. Ostroumov, P.A. Studenikin, E. Heumann, G. Huber, I.A. Shcherbakov, LASERS: Tm3+: GdVO4 — a new efficient medium for diode-pumped 2—μm lasers, Quantum Electron. 27 (1997) 15& ndash;16. [4] B.I. Lazoryak, O.V. Baryshnikova, S.Y. Stefanovich, A.P. Malakho, V.A. Morozov, A.A. Belik, I.A. Leonidov, O.N. Leonidova, G.V. Tandeloo, Ferroelectric and ionicconductive properties of nonlinear-optical vanadate, Ca9Bi(VO4)7, Cheminform 34 (2003) 3003–3010. [5] Z.B. Lin, G.F. Wang, L.Z. Zhang, Growth of a new nonlinear optical crystal YCa9(VO4)7, J. Cryst. Growth 304 (2007) 233–235. [6] Z.B. Lin, F.F. Yuan, S.J. Sun, W. Zhao, L.Z. Zhang, Y.S. Huang, G.F. Wang, Growth, thermal and spectral properties of Nd3+: YCa9(VO4)7 crystal, J. Cryst. Growth 372 (2013) 78–81. [7] P.N. Hu, G.F. Wang, Growth and spectral properties of Er3+: Ca9La(VO4)7 crystal, Mater. Res. Innovations 15 (2011) 75–77. [8] L.Y. Li, G.J. Wang, Y.S. Huang, L.Z. Zhang, Z.B. Lin, G.F. Wang, Crystal growth and spectral properties of Nd3+: Ca9Gd(VO4)7 crystal, J. Cryst. Growth 314 (2011) 331–335. [9] F.F. Yuan, W. Zhao, S.J. Sun, L.Z. Zhang, Y.S. Huang, Z.B. Lin, G.F. Wang, Polarized spectroscopic properties of Er3+: Ca9Y(VO4)7 crystal, J. Lumin. 154 (2014) 241–245. [10] M. Li, S.J. Sun, L.Z. Zhang, F.F. Yuan, Y.S. Huang, Z.B. Lin, Growth and spectral properties of a promising laser crystal Yb3+ /Er3+ : Ca9La(VO4)7, J. Cryst. Growth 451 (2016) 52–56. [11] Z. Zhang, P. Loiko, H. Wu, X. Mateos, J. Serres, H. Lin, W. Chen, G. Zhang, L. Zhang, F. Díaz, Disordered Tm: Ca9La(VO4)7: a novel crystal with potential for broadband tunable lasing, Opt Mater Express 7 (2017) 484–493.

4. Conclusions In this work, we report a novel single crystal Tm3+:Ca10Li(VO4)7, crystal growth, thermal and spectroscopic properties of this crystal were investigated. The crystal can be grown by Czochralski method, annealing in the air is helpful for eliminating the oxygen vacancies, and improve the transparency of the crystal. The thermal expansion 66

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[18] B. Judd, Optical absorption intensities of rare-earth ions, Phys. Rev. 127 (1962) 750. [19] J.J. Shi, B. Liu, L.H. Zheng, Q.G. Wang, H.L. Tang, J.F. Liu, L.B. Su, F. Wu, H.Y. Zhao, N.T. He, N. Li, Q. Li, C. Guo, J. Xu, K.J. Yang, X.D. Xu, W. RybaRomanowski, R. Lisiecki, P. Solarz, Optical study of Tm-doped solid solution (Sc0.5Y0.5)2SiO5 crystal, J. Cryst. Growth 487 (2018) 83–86. [20] M.E. Doroshenko, A.G. Papashvili, E.E. Dunaeva, L.I. Ivleva, V.V. Osiko, H. Jelinkova, J. Sulc, M. Nemec, Spectroscopic and laser properties of SrMoO4: Tm3+ crystal under 1700-nm laser diode pumping, Opt. Mater. 60 (2016) 119–122. [21] R. Lisiecki, P. Solarz, G. Dominiak-Dzik, W. Ryba-Romanowski, M. Sobczyk, P. Černý, J. Šulc, H. Jelínková, Y. Urata, M. Higuchi, Comparative optical study of thulium-doped YVO4, GdVO4, and LuVO4 single crystals, Phys. Rev. B 74 (2006). [22] P. Cerny, J. Oswald, J. Sulc, H. Jelinkova, Y. Urata, M. Higuchi, Multi-watt and tunable diode-pumped operation of Tm: GdVO4 crystal grown by a floating zone method, Adv. Solid-State Photon. (2006). [23] L.I. Ivleva, E.E. Dunaeva, I.S. Voronina, M.E. Doroshenko, A.G. Papashvili, Ca3(VO4)2: Tm3+-A new crystalline medium for 2-μm lasers, J. Cryst. Growth 501 (2018) 18–21.

[12] M.B. Kosmyna, B.P. Nazarenko, V.M. Puzikov, A.N. Shekhovtsov, Development of growth technologies for the photonic single crystals by the czochralski method at institute for single crystals, NAS of Ukraine, Acta Phys. Pol. A 124 (2013) 305–313. [13] 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, Growth, spectroscopic and thermal properties of Nd-doped disordered Ca9(La/Y) (VO4)7 and Ca10(Li/K)(VO4)7 crystals, J. Lumin. 137 (2013) 252–258. [14] M. Kosmyna, B. Nazarenko, V. Puzikov, A. Shekhovtsov, W. Paszkowicz, A. Behrooz, P. Romanowski, A. Yasukevich, N. Kuleshov, M. Demesh, Ca10Li(VO4)7: Nd3+, a promising laser material: growth, structure and spectral characteristics of a Czochralski-grown single crystal, J. Cryst. Growth 445 (2016) 101–107. [15] W. Zhang, P.S. Halasyamani, Z. Gao, S. Wang, J. Wang, X. Tao, Anisotropic thermal properties of the nonlinear optical and polar oxide material Na2TeW2O9, Cryst. Growth Des. 11 (2011) 3636–3641. [16] W. Ge, H. Zhang, J. Wang, J. Liu, H. Li, X. Cheng, H. Xu, X. Xu, X. Hu, M. Jiang, The thermal and optical properties of BaWO4 single crystal, J. Cryst. Growth 276 (2005) 208–214. [17] G. Ofelt, Intensities of crystal spectra of rare-earth ions, J. Chem. Phys. 37 (1962) 511–520.

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