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1Growth, thermal and spectroscopic properties of Tm:MgMoO4
crystal
S.K. Pavlov1'2. K.A. Subbotin12, A.I. Titov12, Y.I. Zimina12, D.A. Lis2, Y.S. Didenko12
1- Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow 2- Mendeleev University of Chemical Technology of Russia, Moscow
In the recent years, the crystal family of divalent metal monotungstates MWO4 (where M = Mg, Zn, Mn, Cd, etc.), has attracted much attention as laser host media for doping with trivalent rare-earth ions. Recently, highly efficient, low-threshold and wavelength-tunable lasing [1,2] have been demonstrated using Tm:MgWO4 crystals. Furthermore, in 2017, the first generation of sub-100 fs pulses from a bulk solid-state laser at ~2 ^m was demonstrated using a Tm:MgWO4 crystal [3]. However, these MgWO4 crystals are grown by the Top-Seeded Solution Growth method.
The MgMoO4 crystal, also known as the molybdate counterpart of MgWO4, melts congruently and can be easily grown by the Czochralski (Cz) method. However, there is no report in the literature on the growth or study of Tm3+-doped MgMoO4 crystals. In the present work, we report on the successful Czochralski growth, as well as the structural, thermal and spectroscopic investigations of both undoped and Tm3+-doped MgMoO4 single crystals.
The single crystals of MgMoO4 and Tm:MgMoO4 were grown by the Cz method. Both crystals exhibited a bright saffron-yellow colour, most likely caused by the hole centers at the molybdenum vacancies. The actual Tm3+ concentration in the MgMoO4 crystal was measured by inductively coupled plasma atomic emission spectroscopy and was 0.1 at.%. Differential thermal analysis was carried out in the temperature range of 20-1400°C with only one sharp thermal effect at 1322°C corresponding to congruent melting/crystallization. Linear thermal expansion coefficients were calculated from high-temperature X-ray powder diffraction analysis. The thermal conductivity of undoped MgMoO4 was measured by the method of stationary longitudinal heat flow in the temperature range of 50 - 300 K along the c-axis. It monotonously decreases with temperature, from 19.51 to 2.64 Wm"1K"1.
The polarized Raman spectra of a b-cut Tm:MgMoO4 crystal contain intense peaks within two
distinct ranges, 122 - 424 cm-1 and 754 - 969 cm-1. For the 3H6 3H4 Tm3+ transition peak absorption cross-section Gabs is 1.60*10-20 cm2 at 794.2 nm corresponding to an absorption full width at half maximum of 6.6 nm. Tm3+ ions in MgMoO4 exhibit a broad and strongly polarized emission band from 1.6 up to 2.15 ^m. The measured luminescence lifetime of the 3F4 excited state was 1.972 ms.
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