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17LS-P-14
Fabrication of laser Ca3(VO4)2:Mn crystals by the method of impurity diffusion from a solid source
I.S. Voronina, E.E. Dunaeva, A.G. Papashvili, L.D. Iskhakova, M.E. Doroshenko, L.I. Ivleva
Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilov str.38, Moscow 119991, Russia irina.voronina. 78@list.ru
Single crystals with disordered structure are widely investigated due to their potential use as a host media for diode-pumped lasers. Inhomogeneous broadening of the spectral lines of these materials provides the good matching between the active element absorption spectrum and the emission lines of laser diodes. Among them, calcium orthovanadate (Ca3(VO4)2, CVO) with disordered whitlockite structure has effective ferroelectric and nonlinear properties, high laser damage threshold and can be used as a multifunctional laser material.
Laser generation in near-IR spectral range was obtained previously in a group of alkali-earth vanadates doped with Mn5+ ions [1]. For the first time Ca3(VO4)2:Mn crystals were grown by Czochralski method [2]. It was shown that Mn ions substitute both Ca2+ (as Mn2+, and Mn3+) and V5+ (as Mn5+) in the medium.
In the work Ca3(VO4)2:Mn crystals were obtained by the high-temperature solid state diffusion method. The samples (thickness plates of 3 mm) were cut from optically homogeneous nominally pure CVO crystals grown by Czochralski method. Manganese oxide Mn2O3 was used as the diffuzant. The annealing regimes were as follows: annealing temperature 1050 - 1300°C; annealing duration - 24 and 48 h; sample orientation [100] and [001]. Diffusion process was carried out in the "open zone" (the sample on the Mn2O3 surface, the air atmosphere), and diffusion process - in the "closed zone" (the sample is immersed in Mn2O3 powder). It was shown that annealing in the closed zone allows to obtain homogeneously doped CVO crystals with ultimate solubility of Mn ions. In the case of open-zone annealing the Mn concentration profile (Fig.1) can be described by the second Fick's law. The diffusion coefficients for different annealing temperatures and crystal orientations were calculated. The activation energy for diffusion process was also estimated. Chemical composition of the annealed crystals was investigated by energy-dispersive X-ray spectroscopy (EDXS) method.
Fig.1. CVO:Mn crystals after diffusion doping at different temperatures.
The optical homogeneity of diffusion doped crystals was investigated by conoscopic method and laser beam diffraction. Ferroelectric domain structure and dislocations were revealed by selective chemical etching. The absorption and luminescence spectra showed the presence of the specific lines for Mn2+, Mn3+and Mn5+. It was estimated that the Mn5+ concentration is higher for diffusion doped CVO in comparison with CZ-grown crystals. Due to this redistribution of dopant ions, the diffusion-doped CVO:Mn crystals can be of great interest for developing lasers based on Mn5+ ions. It was demonstrated that high-temperature solid-state diffusion method is simple enough and effective technique to obtain disordered oxide crystals doped with transition elements having small ionic radii.
[1] L.D. Merkle, H.R. Verdun, B. McIntosh, Spectroscopy and Laser Operation of Mn5+-Doped Vanadates, OSA Proceedings on Advanced Solid-State Lasers, v.15, pp.310-314 (1993), A.A. Pintro and Tso Yee Fan (eds.), https://doi.org/10.1364/ASSL.1993.TL6.
[2] I.S. Voronina, V.V. Voronov, E.E. Dunaeva, L.D. Iskhakova, A.G. Papashvili, M.E. Doroshenko, L.I. Ivleva, Growth and properties of
manganese doped Ca3(VO4)2 single crystals, J. Crystal Growth, v. 555, 125965 (2021) https://doi.org/10.1016/i.icrvsgro.2020.125965.
