Spectroscopy of Eu³⁺ ions in Cd_1−3xEu_2x□_xMoO₄, points out the three main non-equivalent symmetry sites very close to each other, due to the subtle differences in emission. Eu³⁺ ions in this almost ideal red light phosphor possess S₄ point symmetry.

Spectroscopic analysis of Nd ³⁺ in Cd _1−3x Nd _2x □ _x MoO ₄ points out two non-equivalent symmetry sites depending on the location of the □ vacancies. Both short lifetimes and high emission intensities suggest that the compounds could be especially promising for an ultra-short pulse laser generation.

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.

The work presented is mainly focused on synthesis and study of structural and optical properties of microcrystalline Nd³⁺-doped monoclinic dilanthanum dimolybdate at both room and cyrogenic temperatures (4K and 77 K). These compounds might be useful for application in the future as optical materials and also as transparent ceramics when the structure is cubic. The Nd3+-doped phases with monoclinic structure (α-form, space group P21, unit cell parameters a = 7:1426, b = 7:1544, c = 7:1618 Å and β = 89:538°) were observed for a concentration of the optically active ions equal to 5%. When the concentration of the Nd³⁺ ions is higher than 15%, a cubic structure is formed (β-form, space group P2₁3, with the lattice parameter a = 7:155±0:005 Å). A series of Nd³⁺- doped La₂Mo₂O₉ phases with different concentration of Nd³⁺ were prepared using conventional solid-state reactions. The formation of phase-pure Nd³⁺-doped La₂Mo₂O₉ has been monitored by powder X-ray diffraction, DSC, SEM, Raman, and FT-IR absorption techniques. High-resolution absorption and emission spectra, as well as the dynamics of the Nd³⁺ excited states characterized by decay time measurements were recorded from room temperature to 4 K. At least two slightly different crystallographic sites are available for the Nd³⁺ ions. First results show that this new Nd³⁺-doped monoclinic La₂Mo₂O₉ molybdate phosphor is promising for applications of ultra-short pulse lasers.