Impact of Tm3+/Ho3+ co-doping on spectroscopic and laser properties of Ca3(VO4)2 single crystal
Introduction
At the current stage of information technologies and wide application of coherent radiation sources in scientific, engineering, and other fields, researchers are focused not only on extending the functionalities and increasing the efficiency of already existing optical systems but also on creating new systems for controlling laser radiation and information flows. Particularly, great interest is attracted to solid-state nonlinear optical materials, the properties of which can be varied within a wide range due to changes in the main composition and degree of imperfection and due to isomorphous substitution of host ions by ions of rare-earth or transition metals. In the paper we consider the possibilities of creation of effective laser-nonlinear media based on Ca3(VO4)2 co-doped with Tm3+ and Ho3+ ions. It is known that using set of various Tm-doped materials it is possible to cover spectral region from 1.8 up to 2.05 μm [1], [2], [3], [4]. To generate longer wavelengths (around 2.1 μm) usually Ho-doped laser materials are utilized [5], [6], [7], [8], [9]. From other side, Ca3(VO4)2 possesses high nonlinear-optical properties (it can be used as for second harmonic generation as for Raman shifting of laser radiation) and exhibit favorable phase matching conditions in the range between 2 µm and 3 µm. Also, the crystals are characterized by the high damage threshold. Based on doped Ca3(VO4)2 crystalline material new multifunctional media with controllable physicochemical parameters and spectroscopic and laser-nonlinear characteristics can be created.
Section snippets
Experimental details
The Ca3(VO4)2 charge was prepared by solid-state synthesis from 5 N CaCO3 and 5 N V2O5 at 1100 °C during 6 h. Crystals, nominally pure and co-doped with Tm3+ and Ho3+ (in oxide form), were grown from the melt by Czochralski method using a «Nika-3» growth setup from inductively-heated Pt crucibles in air. A conical Pt screen was placed above the crucible to provide needed thermal gradients (60–90 °C/cm in the growth zone and 5–10 °C in the annealing zone). Growth direction was 90° to optical
Results and discussion
The series of rare-earth-doped vanadates based on Ca3(VO4)2 was obtained. Melting point of Ca3(VO4)2 is 1430 °C, it belongs to the R3c space group. This material is known as a high-temperature ferroelectric with Curie temperature Tc = 1113 °C [10]. The general formula rare-earth-doped calcium vanadate can be written as Ca3-3xM2x(VO4)2, where M is (Tm + Ho) element. In this whitlockite-type structure (Fig. 1a) divalent calcium was replaced by trivalent rare earth ions what needs some valence
Conclusion
Calcium orthovanadate crystals co-doped with Tm3+ and Ho3+ ions were successfully grown by Czochralski method. It was shown that the material has good optical homogeneity and can be successfully used as active medium for diode-pumped laser working in the range of 2000 nm. Rather efficient Tm-Ho energy transfer was observed in Ca3(VO4)2:Tm3+ (0.26 at.%)/Ho3+(0.09 at.%) crystal which allowed to obtain 2070 nm lasing of Ho3+ ions under 792 nm thulium pumping. Broad tuning range within about 100 nm
Acknowledgements
This research was supported by the VolkswagenStiftung (Grant № Az. 90.261 from 29.02.2016), the Russian Academy of Sciences (Program I.7) and Czech Science Foundation (project No. 18-11954S).
References (12)
- et al.
Tm3+:CaF2 for 1.9 μm laser operation
Opt. Commun.
(2004) - et al.
Efficient 2.05 μm room temperature Y2SiO5:Tm3+ cw laser
Opt. Commun.
(1993) - et al.
Ca3(VO4)2:Tm3+—A new crystalline medium for 2-μm lasers
J. Cryst. Growth
(2018) - et al.
Spectroscopic and laser properties of Tm3+ ions in Ca3(VO4)2 crystal
J. Lumin.
(2019) - et al.
1.8 μm emission and excited state absorption in LHPG grown Gd0. 8La0.2VO4: Tm3+ single crystal fibers for miniature lasers
Opt. Mater.
(2006) - et al.
Comparative optical study of thulium-doped YAlO3 and GdVO4 single crystals
Laser Phys. Lett.
(2007)