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Abstract
Edge-defined film-fed growth (EFG) was successfully used to grow a Ho3+ doped Sc2O3 crystal. At room temperature, the spectroscopic characteristics of the Ho:Sc2O3 crystal were measured. At 650 nm, 1144 nm, and 1922nm, respectively, the peak absorption cross sections were 0.430 × 10−20 cm2, 0.159 × 10−20 cm2, and 0.513 × 10−20 cm2, with complete widths at half maximum of 16 nm, 22 nm, and 122 nm. The crystal's 5I7→5I8 and 5I6→5I7 peak emission cross-sections were 5.205 × 10−21 cm2 and 5.059 × 10−21 cm2, respectively. The measured fluorescence lifetimes 5I6 and 5I7 were 0.135 ms and 8.389 ms, respectively. The results demonstrated the great potential of Ho:Sc2O3 crystal for 3 µm laser operation.
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1. Introduction
Mid-infrared lasers have a wide range of applications in the industry, military, and communication fields [1,2]. The “molecular fingerprint area” includes the mid-infrared band, where molecules like CO2 and CH4 have distinctive absorption wavelengths [3,4]. Due to water's significant absorption at this wavelength, mid-infrared lasers have several crucial uses in the medical profession, including surgery [5,6].
Ho3+ is one of the most significant active ions used in mid-infrared laser output among the trivalent lanthanide ions. In the past few decades, research on the Ho3+ ion's mid-infrared emission with transitions 5I7→5I8 (∼2 µm) and 5I6→5I7 (∼3 µm) has received a lot of interest [7,8]. Ho3+ ion lasing for the 2 µm transition from 5I7 to 5I8 has so far been proven in the matrices of YAG, BaY2F8, YLF, CYA, CNGG, YAP, and SSO [9–15]. Besides, a continuous-wave (CW) laser output power of 5.2 W and a slope efficiency of 52% at 2124 nm of Ho:Lu2O3 laser rod has been reported in 2012 [16], Meanwhile, diode-pumped ∼2 µm Q-switched Ho:Lu2O3 laser also has been realized, the maximum pulse energy exceeded 5 mJ at 100 Hz pulse repetition rate and the maximum peak power was 23 kW [17]. And Ho3+ ion lasing for 5I6→5I7 (∼3 µm) transition has been demonstrated in the matrix of YAP, KYF4, ZBLAN, GYSGG, and LLF [18–24]. Additionally, Ho3+ doped laser materials have the advantages of larger emission cross sections and longer lifetime, it’s important to further improve the spectroscopic properties and make stable continuous-wave laser output [25].
Superior thermo-mechanical characteristics, such as exceptional hardness and good heat conductivity, can be found in sesquioxide host materials. The cubic crystal system and low birefringence of the rare earth sesquioxide crystal matrix (Lu2O3, Sc2O3, Y2O3) are only two of its many benefits. The Sc2O3 crystal has low phonon energy of 672 cm−1 and high thermal conductivities of 16.5 Wm−1K−1 [26]. The Ho3+ ion's 3 µm laser output benefits from the low phonon energy's ability to minimize non-radiation relaxation. The traits all point to Sc2O3 crystal as a potential laser host material. Only a few pieces of research have been conducted on the rare earth ion doped Sc2O3 laser crystal due to the material's extremely high melting point of 2430 °C and the difficulty in growing good optical quality and big Sc2O3 single crystals.
In this paper, we have successfully grown high-quality Ho3+ doped Sc2O3 crystals and analyzed the structure, spectra, and J-O theory.
2. Experimental procedure
In an induction heated furnace, a Ho3+ doped Sc2O3 crystal was grown using the EFG (Edge-Definde Film-Fed Growth) method. The following molar compositions of 99.99% pure Sc2O3 and Ho2O3 powders have been used, respectively: 1 at.% Ho2O3 and 99 at.% Sc2O3. After being compressed into bulks, the combined powders were added to the tungsten crucible. The argon gas was added to the furnace as a protective atmosphere when the air pressure within the furnace dropped to 8 Pa. The crucible was then maintained at 2430°C for one hour. The growth rate is 2–10 mm/h. The grown Ho3+ doped Sc2O3 crystal is seen in Fig. 1.
The agate mortar was used to grind the powder samples for the XRD experiments, and a Bruker SMART APEX II 4 K CCD diffractometer with Cu Kα (50 kV, 40 mA) irradiation (λ=0.71073 Å) was used to record the results. The XRD data was recorded at the 2θ angle from 20° to 70° with a scanning rate of 0.015° and an exposure time of 0.9 s. To determine the cell properties of the grown crystals, the XRD curves were analyzed using the Jade 6.0 program.
The samples’ absorption spectra between 400 and 2200 nm were measured using a Spectrometer (Cary 5000). The FLS 1000 (Edinburgh Instruments, England) was used to measure the emission spectra and decay time in the wavelength ranges of 1700–2300 nm and 2700–3200 nm when excited by an 640 nm pump. At room temperature, all measurements were made.
3. Results and discussion
3.1 Crystal structure
As shown in Fig. 2, it can be seen from the figure that the diffraction peaks of the sample compare well with the diffraction peaks of the standard card of Sc2O3 (PDF#43-1028), and the peak positions and relative intensities of the diffraction peaks match well with the standard PDF card, indicating that the doping of Ho3+ ions does not affect the structure of Sc2O3 single crystals, and the crystal quality is good. The cell parameter of the crystal calculated by Jade software is 9.838 Å, and the cell parameter of pure Sc2O3 crystal is 9.844 Å. It can be seen that the cell parameter of the doped crystal is slightly lower than that of pure Sc2O3 crystal, although the radius of Ho3+ ions (0.901 Å) is larger than that of Sc3+ ions (0.750 Å), the cell parameter is reduced, which may be due to the doping of Ho3+ ions doping caused a shrinking trend in the Sc2O3 cell [26,27].
The concentration of Ho3+ ion in Ho:Sc2O3 crystal was measured to be 1.01 × 1020 cm−3 by ICP-AES. Thus, the segregation coefficient η of Ho3+ ion in Ho:Sc2O3 crystal is 0.63. The value is close 1.0, which indicates that Ho3+ is easy to incorporate into the Sc3+ sites.
3.2 Absorption spectra
Absorption spectra of 1.0at.% Ho:Sc2O3 crystal samples were measured at room temperature in the range 400-2200 nm, as shown in Fig. 3, where six major absorption peaks of Ho3+ ions in this range are marked, corresponding to the ground state 5I8 energy level to 5G5, 5F1 + 5G6, 5S2 + 5F4, 5F5, 5I6 and 5I7. The energy level jumps correspond to wavelengths of 416 nm, 449 nm, 536 nm, 650 nm, 1144 nm, and 1922nm, corresponding to half-peak widths of 8 nm, 3 nm, 7 nm, 16 nm, 22 nm, and 122 nm, and corresponding absorption cross sections of 0.315 × 10−20 cm2, 6.089 × 10−20 cm2, 0.662 × 10−20 cm2, 0.430 × 10−20 cm2, 0.159 × 10−20 cm2, and 0.513 × 10−20 cm2, which is smaller than Ho:GdScO3 and Ho:Lu2O3 [28,29]. In our spectral measurements and corresponding laser tests, we mainly refer to the absorption at 650 nm, 1144 nm, and 1922nm.
3.3 Analysis of J-O theory
Based on the absorption spectra of 1.0at.% Ho:Sc2O3 crystals, the J-O intensity parameters Ωt (t = 2,4,6) of 1.0at.% Ho:Sc2O3 crystals were calculated using J-O theory [30–32], which was 4.522 × 10−20 cm2, 1.887 × 10−20 cm2, 0.934 × 10−20 cm2, The relatively high Ω2 values of 1.0at.% Ho:Sc2O3 crystals indicate that Ho3+ ion doping makes the crystals more covalent, and the high Ω2, also indicates that the symmetry around the doped ions is also lower after doping, while the spectral quality factor Ω4/Ω6 is: 2.021, which is greater than that of oxide YAG crystals (1.41), LuAG crystals (1.08), YAP (1.55), LLF (1.05), LaF3 (1.57), CaF2 (0.97), and ZnWO4 (0.33) indicating that Ho:Sc2O3 crystals have higher spectral quality than these crystals [33–38]. The intensity parameters of some other Ho3+ doped crystals are also listed in Table 1 for comparison. The parameters such as spontaneous radiation chance, radiation lifetime, and a fluorescence branching ratio of 1.0at.% Ho:Sc2O3 crystals were also calculated, as shown in Table 2, from which it can be seen that the radiation lifetime of 5I6 energy level is 4.176 ms and the fluorescence branching ratio is 18.533%, and the radiation lifetime of 5I7 energy level is 8.280 ms.
Table 1. The J-O intensity parameters of Ho3+ doped crystals.
Table 2. Radiative transition rates A(J-J′), branching ratios βJJ′ and radiative lifetime τrad of Ho:Sc2O3 crystal.
3.4 Emission spectra
The ∼2 µm band and ∼3 µm band fluorescence spectra of 1.0at.% Ho:Sc2O3 crystals were measured using LD pump excitation at 640 nm at room temperature, as shown in Fig. 4, and the measured ranges were 1700-2300 nm and 2700-3200 nm, respectively, for the ∼2 µm band with a peak wavelength of 2124 nm and a half-peak width of 150 nm, which is similar to the half-peak width of Ho:CaF2 crystals [42]. The wide fluorescence bandwidth is conducive to the realization of ultrafast and tunable laser output, and the emission cross section of the ∼2 µm band is 5.205 × 10−21 cm2 calculated by the F-L formula [43];
3.5 Fluorescence lifetime
The 5I7 and 5I6 fluorescence lifetimes of 1.0at.% Ho:Sc2O3 crystals were measured using LD pump excitation at 640 nm at room temperature, and the fluorescence lifetime decay curves were obtained by fitting a single exponential function, as shown in Fig. 5. The fluorescence lifetime of the 5I7 energy level is obtained as 8.389 ms, and that of the 5I6 energy level is 0.135 ms. We found that the fluorescence lifetime of energy level 5I6 in the ∼3 µm band is relatively short in Sc2O3 crystals, which may be due to the severely excited state absorption and upconversion of 5I6 energy level in the relatively strong field matrix of Sc2O3 compared with the weak field matrix of CaF2 and LYF etc. [42,44], while the lifetime of the energy level 5I7 in the ∼2 µm band is comparable to that of other matrices.
4. Conclusions
In conclusion, the EFG approach proved effective in growing the Ho:Sc2O3 crystal. For the first time, the spectral characteristics and J-O analyses were studied. Ho:Sc2O3 crystal's absorption spectrum, fluorescence spectra, and fluorescence decay curves were measured and analyzed. With FWHMs of 22 nm and 16 nm, the peak absorption cross-sections at 1144 nm and 650 nm were determined to be 0.159 × 10−20 cm2 and 0.430 × 10−20 cm2 respectively. The calculated values for the effective Judd-Ofelt parameters Ω2, Ω4, and Ω6 are 4.522 × 10−20 cm2, 1.887 × 10−20 cm2, and 0.934 × 10−20 cm2, respectively. The crystal's 5I7→5I8 and 5I6→5I7 peak emission cross-sections were 5.205 × 10−21 cm2 and 5.059 × 10−21 cm2, respectively. The5 I6 and 5I7 multiplets’ fluorescence lifetimes were measured to be 0.135 ms and 8.389 ms, respectively. The totality of the data points to Ho:Sc2O3 crystal as a potential laser material for 3 µm laser operation. And the outstanding performance of Ho:Sc2O3 at 2 µm shows that it has strong application prospects in environmental monitoring and coherent Doppler velocimetry.
Funding
National Natural Science Foundation of China (No.52032009, No.61621001, No.61805177, No.61861136007).
Acknowledgment
This work is partially supported by National Natural Science Foundation of China (No.61805177, No.52032009, No.61861136007, and No. 61621001).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. A. Godard, “Infrared (2–12 µm) solid-state laser sources: a review,” C. R. Phys. 8(10), 1100–1128 (2007). [CrossRef]
2. U. Willer, M. Saraji, A. Khorsandi, P. Geiser, and W. Schade, “Near- and mid-infrared laser monitoring of industrial processes, environment and security applications,” Opt. Lasers Eng. 44(7), 699–710 (2006). [CrossRef]
3. M. Ebrahim-Zadeh and K. Vodopyanov, “Mid-infrared coherent sources and applications: introduction,” J. Opt. Soc. Am. B 33(11), MIC1 (2016). [CrossRef]
4. L. S. Rothman, R. R. Gamache, R. H. Tipping, C. P. Rinsland, M. A. H. Smith, D. C. Benner, V. M. Devi, J.-M. Flaud, C. Camy-Peyret, A. Perrin, A. Goldman, S. T. Massie, L. R. Brown, and R. A. Toth, “The HITRAN molecular database: Editions of 1991 and 1992,” J. Quant. Spectrosc. Radiat. Transfer 48(5-6), 469–507 (1992). [CrossRef]
5. I. T. Sorokina and K. L. Vodopyanov, Solid-State Mid-Infrared Laser Sources (Springer Science & Business Media, 2003).
6. R. Kaufmann, A. Hartmann, and R. Hibst, “Cutting and skin-ablative properties of pulsed mid-infrared laser surgery,” J. Dermatol. Surg. Oncol. 20(2), 112–118 (1994). [CrossRef]
7. D. Lande, S. S. Orlov, A. Akella, L. Hesselink, and R. R. Neurgaonkar, “Digital holographic storage system incorporating optical fixing,” Opt. Lett. 22(22), 1722–1724 (1997). [CrossRef]
8. J. Peng, H. Xia, P. Wang, H. Hu, L. Tang, Y. Zhang, H. Jiang, and B. Chen, “Optical spectra and gain properties of Ho3+/Pr3+ co-doped LiYF4 crystal,” J. Mater. Sci. Technol. 30(9), 910–916 (2014). [CrossRef]
9. X. Yang, T. Qiao, T. Gao, A. Guo, Z. Jiang, F. Tian, Y. Mu, S. Chen, Z. Zhang, C. He, G. Wang, Y. He, and X. Liu, “34.7 W passive peak power Q-switch Ho:Sc2SiO5 laser operating at 2 µm with a few-layer molybdenum disulfide saturable absorber,” Optik 226, 165486 (2021). [CrossRef]
10. L. F. Johnson, J. E. Geusic, and L. G. Van Uitert, “Coherent oscillations from Tm3+, Ho3+, Yb3+ and Er3+ ions in yttrium aluminum garnet,” Appl. Phys. Lett. 7(5), 127–129 (1965). [CrossRef]
11. J. Tang, E. Li, F. Wang, W. Yao, C. Shen, and D. Shen, “High power Ho:YAP laser with 107 W of output power at 2117 nm,” IEEE Photonics J. 12(2), 1–7 (2020). [CrossRef]
12. E. Ji, Q. Liu, M. Nie, X. Cao, X. Fu, and M. Gong, “High-slope-efficiency 2.06 µm Ho:YLF laser in-band pumped by a fiber-coupled broadband diode,” Opt. Lett. 41(6), 1237–1240 (2016). [CrossRef]
13. F. Cornacchia, E. Sani, A. Toncelli, M. Tonelli, M. Marano, S. Taccheo, G. Galzerano, and P. Laporta, “Optical spectroscopy and diode-pumped laser characteristics of codoped Tm-Ho:YLF and Tm-Ho:BaYF : a comparative analysis,” Appl. Phys. B: Lasers Opt. 75(8), 817–822 (2002). [CrossRef]
14. Y. Xue, N. Li, Q. Song, X. Xu, X. Yang, T. Dai, D. Wang, Q. Wang, D. Li, Z. Wang, and J. Xu, “Spectral properties and laser performance of Ho:CNGG crystals grown by the micro-pulling-down method,” Opt. Mater. Express 9(6), 2490–2496 (2019). [CrossRef]
15. J. Zhang, D. Shen, X. Xu, and H. Chen, “Widely tunable, narrow line-width Ho:CaYAlO4 laser with a volume Bragg grating,” Opt. Mater. Express 6(6), 1768–1773 (2016). [CrossRef]
16. S. Lamrini, S. Lamrini, P. Koopmann, P. Koopmann, M. Schäfer, K. Scholle, P. Fuhrberg, K. Petermann, and G. Huber, “Efficient Laser Operation of Ho:Lu2O3 at Room Temperature,” in CLEO/Europe and EQEC 2011 Conference Digest (2011), Paper CA1_6 (Optica Publishing Group, 2011), p. CA1_6.
17. S. Lamrini, P. Koopmann, K. Scholle, P. Fuhrberg, and G. Huber, “Diode pumped Q-switched Ho:Lu2O3 laser at 2.12 µm,” in 2012 Conference on Lasers and Electro-Optics (CLEO) (2012), pp. 1–2.
18. S. R. Bowman, W. S. Rabinovich, A. P. Bowman, B. J. Feldman, and G. H. Rosenblatt, “3 µm Laser Performance of Ho:YAlO3 and Nd,Ho:YAlO3,” IEEE J. Quantum Electron. 26(3), 403–406 (1990). [CrossRef]
19. A. Diening, P. Möbert, E. Heumann, G. Huber, and B. Chai, “Diode-pumped CW lasing of Yb,Ho:KYF4 in the 3µm spectral range in comparison to Er:KYF4,” Laser Phys. 165(1-3), 71–75 (1999). [CrossRef]
20. S. D. Jackson, “Single-transverse-mode 2.5-W holmium-doped fluoride fiber laser operating at 2.86 µm,” Opt. Lett. 29(4), 334–336 (2004). [CrossRef]
21. J. Li, D. D. Hudson, and S. D. Jackson, “High-power diode-pumped fiber laser operating at 3 µm,” Opt. Lett. 36(18), 3642–3644 (2011). [CrossRef]
22. S. Crawford, D. D. Hudson, and S. Jackson, “3.4 W Ho3+, Pr3+ co-doped fluoride fibre laser,” in CLEO: 2014 (OSA, 2014), p. STu1L.3.
23. H. Zhang, D. Sun, J. Luo, F. Peng, Z. Fang, X. Zhao, C. Quan, M. Cheng, Q. Zhang, and S. Yin, “Growth, spectroscopy, and laser performance of a radiation-resistant Cr,Yb,Ho,Pr:GYSGG crystal for 2.84 µm mid-infrared laser,” J. Lumin. 194, 636–640 (2018). [CrossRef]
24. H. Nie, P. Zhang, B. Zhang, M. Xu, K. Yang, X. Sun, L. Zhang, Y. Hang, and J. He, “Watt-level continuous-wave and black phosphorus passive Q-switching operation of Ho3+,Pr3+:LiLuF4 bulk laser at 2.95 µm,” IEEE J. Sel. Top. Quantum Electron. 24(5), 1–5 (2018). [CrossRef]
25. K. L. Vodopyanov, “Mid-infrared optical parametric generator with extra-wide (3–19-µm) tunability: applications for spectroscopy of two-dimensional electrons in quantum wells,” J. Opt. Soc. Am. B 16(9), 1579–1586 (1999). [CrossRef]
26. V. Petrov, K. Petermann, U. Griebner, V. Peters, J. Liu, M. Rico, P. Klopp, and G. Huber, “Continuous-wave and Mode-locked Lasers Based n ubic Sesquioxide Crystalline Hosts,” in G. L. Wood and M. A. Dubinskii, eds. (2006), p. 62160 H.
27. P. Fu, Z. Xu, R. Chu, X. Wu, W. Li, and H. Zhang, “Structure and electrical properties of the Ho2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics,” J. Mater. Sci.: Mater. Electron. 23(12), 2167–2172 (2012). [CrossRef]
28. J. Dong, W. Wang, Y. Xue, W. Hou, X. Cao, X. Xu, F. Wu, P. Luo, Q. Wang, D. Li, and J. Xu, “Crystal growth and spectroscopic analysis of Ho:Lu2O3 crystal for mid-infrared emission,” J. Lumin. 251, 119192 (2022). [CrossRef]
29. D. Hu, J. Dong, J. Tian, W. Wang, Q. Wang, Y. Xue, X. Xu, and J. Xu, “Crystal growth, spectral properties and Judd-Ofelt analysis of Ho:GdScO3 crystal,” J. Lumin. 238, 118243 (2021). [CrossRef]
30. B. R. Judd, “Optical absorption intensities of rare-earth ions,” Phys. Rev. 127(3), 750–761 (1962). [CrossRef]
31. G. S. Ofelt, “Intensities of crystal spectra of rare-earth ions,” J. Chem. Phys. 37(3), 511–520 (1962). [CrossRef]
32. W. T. Carnall, P. R. Fields, and K. Rajnak, “Electronic energy levels in the trivalent lanthanide aquo ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+,” J. Chem. Phys. 49(10), 4424–4442 (1968). [CrossRef]
33. S. A. Payne, L. K. Smith, and W. F. Krupke, “Cross sections and quantum yields of the 3 µm emission for Er3+ and Ho3+ dopants in crystals,” J. Appl. Phys. 77(9), 4274–4279 (1995). [CrossRef]
34. D. N. Patel, B. R. Reddy, and S. K. Nash-Stevenson, “Spectroscopic and two-photon upconversion studies of Ho3+-doped Lu3Al5O12,” Opt. Mater. 10(3), 225–234 (1998). [CrossRef]
35. M. J. Weber, B. H. Matsinger, V. L. Donlan, and G. T. Surratt, “Optical Transition Probabilities for Trivalent Holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972). [CrossRef]
36. C. Zhao, Y. Hang, L. Zhang, J. Yin, P. Hu, and E. Ma, “Polarized spectroscopic properties of Ho3+-doped LuLiF4 single crystal for 2 µm and 2.9 µm lasers,” Opt. Mater. 33(11), 1610–1615 (2011). [CrossRef]
37. F. Yang, C. Tu, H. Wang, Y. Wei, Z. You, G. Jia, J. Li, Z. Zhu, X. Lu, and Y. Wang, “Growth and spectroscopy of ZnWO4:Ho3+ crystal,” J. Alloys Compd. 455(1-2), 269–273 (2008). [CrossRef]
38. B. M. Walsh, G. W. Grew, and N. P. Barnes, “Energy levels and intensity parameters of Ho3+ ions in GdLiF4, YLiF4 and LuLiF4,” J. Phys.: Condens. Matter 17(48), 7643–7665 (2005). [CrossRef]
39. S. R. Bullock, B. R. Reddy, P. Venkateswarlu, and S. K. Nash-Stevenson, “Site-selective energy upconversion in CaF2:Ho3+,” J. Opt. Soc. Am. B 14(3), 553–559 (1997). [CrossRef]
40. S. Gołvab, P. Solarz, G. Dominiak-Dzik, T. Lukasiewicz, M. Świrkowicz, and W. Ryba-Romanowski, “Spectroscopy of YVO4:Ho3+ crystals,” Appl. Phys. B 74(3), 237–241 (2002). [CrossRef]
41. X. Ma, Z. Zhu, J. Li, Z. You, Y. Wang, and C. Tu, “Optical properties of Ho3+:SrMoO4 single crystal,” Mater. Res. Bull. 44(3), 571–575 (2009). [CrossRef]
42. B. Lal and D. Ramachandra Rao, “Fluorescence and lifetime studies of Ho3+: CaF2,” Chem. Phys. Lett. 53(2), 250–254 (1978). [CrossRef]
43. J. A. Caird, A. J. Ramponi, and P. R. Staver, “Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses,” J. Opt. Soc. Am. B 8(7), 1391–1403 (1991). [CrossRef]
44. J.-T. Peng, H.-P. Xia, P.-Y. Wang, H.-Y. Hu, and L. Tang, “Mid-infrared emission properties of Ho3+ doped LiYF4 single crystals,” Journal of Inorganic Materials 25(5), 546–550 (2010). [CrossRef]
