Structural and spectroscopic characterizations of new Cd1−3xNd2x□xMoO4 scheelite-type molybdates with vacancies as potential optical materials

Abstract

The necessity to develop new laser materials of tungstates and molybdates is our motivation to study a new family of molybdates activated by Nd³⁺ ions, which crystallizes in the scheelite-type structure (the tetragonal symmetry, the space group I4₁/a). A series of Cd_1−3xNd_2x□_xMoO₄ stable solid solutions with concentration of Nd³⁺ ions from 0.1 mol% to 66.67 mol% with respect to Cd²⁺ ions were successfully synthesized by a high-temperature annealing, using CdMoO₄ and Nd₂(MoO₄)₃ as the starting materials. Structural and spectroscopic characterizations of Nd³⁺ substituting Cd²⁺ ions were carried out. The substitution of divalent Cd²⁺ by trivalent Nd³⁺ cations leads to the formation of cationic vacancies in the framework (which are denoted in the chemical formula as □). The Nd³⁺ ions in this matrix occupy two non-equivalent symmetry sites depending on the location of these vacancies. Concentration of vacancies depends essentially on the composition of initial CdMoO₄–Nd₂(MoO₄)₃ mixtures. The SEM analysis of crystal morphology reveals high homogeneity of the nearly-spherical shaped products with an average grain size of about 1–10 μm. Optical analysis and the laser parameters suggest that Cd_1−3xNd_2x□_xMoO₄ can be considered as a potential laser material. Both the values of the absorption cross-section and the strong emission of the ⁴F_3/2 → ⁴I_11/2 laser channel of Nd³⁺ recorded under LED source excitation or OPO laser pumping, as well as the radiative lifetimes of NIR luminescence, are appropriate for potential applications of this optical material as a solid state laser.