CC BY
18LS-PS-9
Growth and polarization-resolved spectroscopy of monoclinic Yb3+:ZnWO4 crystals
D. Lis1, P. Loiko2, K. Subbotin1, E. Zharikov1, A. Titov1, J.M. Serres3, M. Aguilo3, F. Diaz3, X. Mateos3
1Prokhorov General Physics Institute of the Russian Academy of Sciences, Laser Materials and Technology Research Center at GPI, Moscow, Russian Federation 2ITMO University, Department of Optical Physics and Modern Natural Science, St. Petersburg, Russian Federation
3Universitat Rovira i Virgili, Fisica i Cristallografia de Materials i Nanomaterials, Tarragona, Spain
Monoclinic wolframite-type monotungstate crystals M2+WO4 (where M = Mg, Zn, Mn, Ni, etc.) are the promising laser hosts for doping with trivalent rare-earth ions (RE3+). They possess good thermo-mechanical properties, strong Raman activity and provide broad and strong absorption and emission bands for the RE3+ ions with polarized light. Recently efficient laser operation in the near-infrared was demonstrated at RE3+-doped MgWO4 crystals. In the present work, we report on Czochralski (Cz) growth, structure, vibronic properties and polarized room- and low-temperature spectroscopic studies of an Yb3+-doped zinc monotungstate crystal. ZnWO4:5 at.% Yb3+:5 at.% Li+: crystal (nominal composition) was grown by the Cz method along the [100] direction from melt in air from a platinum-rhodium crucible. Pulling rate was 1 mm/h, rotation rate 6 rpm. After growth the crystal was cooled to 300K with the speed of 8 K/h. The initial charge was prepared from a mixture of ZnO, WO3, Yb2O3 and Li2CO3 of high purity grade. Lithium ions were added to ensure the change compensation. The solid-phase powder synthesis of the preliminarily carefully mixed charge was performed at 900°C for 12 h. The structure (monoclinic, sp. gr. C42h -P2/c) and the phase purity of the crystals were confirmed by X-ray diffraction. The crystals exhibited a cleavage along the (010) plane. Polarized Raman spectra were measured for the crystal. The most intense Raman band is at ~904 cm-1. ZnWO4 is an optically biaxial crystal: only one of the optical indicatrix axes (X) coincides with the 2-fold axis (b) and the other two ones (Y and Z) are located in the a-c plane. The Yb3+,Li:ZnWO4 crystals for the spectroscopic studies were oriented in the frame of the optical indicatrix. Absorption and luminescence spectra of Yb3+ ions corresponding to the 2F7/2 ^ 2F5/2 transition were measured for light polarizations E || X, Y, Z. The spectra are strongly polarized. The maximum stimulated-emission cross-section is 2.82* 10-20 cm2 at 1055.5 nm for light polarization E || X and the emission bandwidth is ~12 nm. The lifetime of Yb3+ ions is 367 p,s; the luminescence decay is single-exponential. The Stark splitting is resolved using low-temperature (6 K) spectroscopy. The Yb3+:ZnWO4 crystal is promising for CW and mode-locked lasers at ~1 p,m.
