Structural and spectroscopic characterizations of two promising Nd-doped monoclinic or tetragonal laser tungstates

Abstract

The tetragonal Cd_0.25Nd_0.50□_0.25WO₄ compound (□ – statistically distributed vacancies in cation sublattice) and its gadolinium diluted Cd_0.25Gd_0.50□_0.25WO₄:Nd³⁺ analogue as well as the monoclinic CdNd₂W₂O₁₀ phase and its yttrium diluted CdY₂W₂O₁₀:Nd³⁺ analogue were synthesized by the high temperature solid-state reaction. The gadolinium or yttrium diluted samples were doped with different concentrations of the active Nd³⁺ ion: 0.25, 0.5, 2.5 and 5 mol%. X-ray powder diffraction, IR spectra as well as electron microscopy (SEM and HRTEM) were used to identify their structure and morphology. All micromaterials were obtained as spherical particles with average diameters between 1 and 10 μm. In order to study their spectroscopic properties, high resolution absorption and emission spectra in the visible and IR regions were measured at room temperature, 77 K and 4 K. The kinetics of luminescence from the lowest ⁴F_3/2 energy level as a function of the Nd³⁺ ion concentration and temperature is also reported. Both the values of the absorption cross-section calculated for 5 mol% of Nd³⁺ ion, and the very strong emission of the ⁴F_3/2 → ⁴I_11/2 laser channel of Nd³⁺ recorded under Xe lamp excitation or OPO laser pumping, indicate that the scheelite-type Cd_0.25Gd_0.50□_0.25WO₄:Nd³⁺ phase can be considered as a promising laser material. The radiative lifetimes of IR luminescence are also appropriate for potential applications of this phosphor as a solid-state laser.