Facile hydrothermal synthesis and luminescent properties of monodisperse ellipsoid-like NaLa(MoO₄)₂:Sm³⁺ red-emitting phosphors

Monodisperse ellipsoid-like NaLa(MoO₄)₂:Sm³⁺ micro-particles were prepared by a facile hydrothermal method at 180 °C for 12 h without using any additives. The crystal structure, micro-morphology and luminescent property of as-synthesized phosphors were characterized by powder X-ray diffraction, scanning electron microscopy and fluorescent spectrophotometer. The results show that the starting pH values are responsible for the formation of pure tetragonal phase and uniform ellipsoid-like NaLa(MoO₄)₂:Sm³⁺ micro-particles. A possible morphological formation mechanism of the ellipsoids has been presented according to time-dependent experiments. The main emission peak of ellipsoid-like NaLa(MoO₄)₂:Sm³⁺ is located at 647 nm under the excitation of 405 nm, which is originated from the electric dipole transition of ⁴G_5/2 → ⁶H_9/2 of Sm³⁺ (red-emitting). Furthermore, it is found that the luminescent intensity is influenced by the starting pH values, the hydrothermal reaction time and the concentration x of Sm³⁺. Meanwhile, the mechanism of concentration quenching of Sm³⁺ has been determined to the electric dipole–dipole interaction on the basis of the relevant theory and experiment data. Because of a strong red emission under the excitation of near-ultraviolet, ellipsoid-like NaLa(MoO₄)₂:Sm³⁺ phosphors may have potential application in the fields of field emission displays, solid state lighting and optoelectronic devices.