Fabrication of Eu³⁺ and Sm³⁺ codoped micro/nanosized MMoO₄ (M = Ca, Ba, and Sr) via facile hydrothermal method and their photoluminescence properties through energy transfer

Eu³⁺ and Sm³⁺ codoped micro/nanosized MMoO ₄ (M = Ca, Ba, Sr) phosphors with various shapes have been synthesized via a facile hydrothermal method with surfactant-free environment. The morphology of the materials was found to be manipulated by the pH value of the precursor solution. MMoO₄:Eu³⁺, Sm³⁺ (M = Ca, Ba, Sr) nanoflakes, microflowers, cubes, and spheres were obtained and characterized by X-ray diffraction and field emission scanning electron microscopy. The luminescent properties of the molybdate phosphors were systematically studied. The introduction of Sm³⁺ into each of the red-emitting phosphors MMoO₄:Eu³⁺ (M = Ca, Ba, Sr) can generate a strong excitation line at 405 nm, originating from the ⁶H_5/2 → ⁶P_5/2 transition of Sm³⁺, significantly extending the excitation region for matching the near-ultraviolet light-emitting diodes (∼400 nm). Energy transfer from Sm³⁺ to Eu³⁺ was observed in the whole MMoO₄ systems and investigated in detail in CaMoO₄ as a function of Sm ³⁺ concentrations. A back-energy transfer was also evidenced by the shortening of the ⁵D₀ lifetimes of Eu³⁺ with increasing Sm³⁺ concentrations.