Luminescence and magnetic behaviour of almond like (Na_0.5La _0.5)MoO₄:RE³⁺ (RE = Eu, Tb, Dy) nanostructures

Tetragonal phase (Na_0.5La_0.5)MoO₄:RE ³⁺ (RE = Eu, Tb, Dy) with almond like hierarchical structures assembled from nanosheets building blocks were successfully synthesized by employing disodium ethylenediaminetetraacetic acid (Na₂EDTA) using hydrothermal route at 200 °C for 24 h. Field emission scanning electron microscope, transmission electron microscope, and X-ray diffraction patterns were used to characterize the morphology, size, and crystal structure with good resolution. The sequestering agent EDTA acts as quadridentate ligand coordinated with metal ions [Na⁺, La³⁺/RE³⁺] facilitating the formation of self-organized 3D networks. The growth mechanism for the formation of almond like nanostructures is explicated in four paths: dissolution, adsorption, in situ transformation in acidic and basic media and the effective collision. Photoluminescence excitation and emission spectra reveals a spectral blue shift which was observed in the nanosamples towards shorter wavelengths compared with the bulk sample. Upon UV irradiation, both bulk and nanostructure show strong luminescence in the red region due to the ⁵D₀ → ⁷F₂ transition in Eu ³⁺. Also, Tb³⁺ and Dy³⁺ doped (Na _0.5La_0.5)MoO₄ phosphor exhibit green and yellow luminescence due to the transitions ⁵D₄ → ⁷F₅ and ⁴F_9/2 → ⁶H_13/2, respectively. Color richness and fluorescence decay times for major emission lines in Eu³⁺, Tb³⁺, and Dy³⁺, that were determined to be x = 0.593, y = 0.326, τ = 0.417 ms; x = 0.228, y = 0.619, τ = 0.411 ms; x = 0.3851, y = 0.4334, τ = 0.403 ms, respectively. The as-synthesized nanophosphor exhibits weak ferromagnetic hysteresis with significant remnant magnetization (1.84E ^-4 emu/gm) at room temperature in comparison with bulk sample. The above results suggesting these materials can serve as excellent luminescence markers which being controlled by external magnetic field.