Trivalent Neodymium-Doped Double Molybdate/Tungstate Composite Laser Crystals

The use of inhomogeneous broadening in composite disordered crystals has been widely recognized as a successful approach to enhancing the spectral bandwidth of rare-earth ions in optical spectra. In this study, composite disordered laser crystals of rare-earth alkali metal double molybdate/tungstate, doped with 2 atom % Nd3+ and represented by the general formula Nd:NaGd(MoxW1–xO4)2 (x = 0.5, 0.7 and 0.9), were grown using the Czochralski method. The crystal structure of the disordered laser crystals was determined to be of the tetragonal phase with a space group of I41/a, as confirmed through X-ray diffraction (XRD) and Rietveld refinement analyses. The spectroscopic properties of the disordered laser crystal, encompassing absorption, emission, and fluorescence decay characteristics were investigated. The (MoO4)1.0(WO4)1.0 composite crystal exhibited an exceptionally broad absorption bandwidth, with a full width at half-maximum (FWHM) of 21 at 808 nm, approximately 10 times wider than that of the well-known Nd:YAG crystal. Moreover, the composite crystal demonstrated the generation of a continuous-wave 1.06 μm laser, which was further frequency-doubled to produce a 532 nm laser. Additionally, the passively Q-switched laser behavior of the composite crystal at 1.06 μm was explored, utilizing tungsten disulfide as a saturable absorber. In summary, the double molybdate/tungstate composite disordered crystal exhibits advantageous characteristics, such as a low melting point (approximately 1200 °C), stable physical–chemical properties, and remarkable spectroscopic properties. These features highlight the potential applications of these composite crystals in all solid-state lasers. High-quality Nd-doped double molybdate/tungstate composite disordered laser crystals were grown by the Czochralski method. By implementing a composite engineering strategy, an exceptionally inhomogeneous spectral broadening with an fwhm of up to 21 at 808 nm was achieved.