Synthesis and optical characterization of host sensitized color tunable Tb_2−xEu_x(MoO₄)₃ nanophosphors for optoelectronic applications

In the present work, host sensitized multicolor emitting Tb_2−xEu_x(MoO₄)₃ nanophosphors was synthesized by sol–gel method for the first time. The X-ray diffraction, transmission electron microscopy (TEM), photoluminescence studies and fluorescent lifetime measurements were employed to characterize the samples. The X-ray diffraction and TEM analysis revealed the orthorhombic structure and nanosize of the phosphors. Photoluminescence spectra, concentration effect, fluorescence lifetime and chromaticity variations were performed to study the luminescence properties. These studies suggest that, these phosphors could be effectively excited in a wavelength range from 300 to 485 nm, which matches well with that for nUVLED chips. The sensitization of Eu³⁺ emission through MoO₄ ²⁻ → Eu³⁺ and Tb³⁺ to Eu³⁺ energy transfer schemes and energy transfer from MoO₄ ²⁻ → Tb³⁺ are investigated in detail. The energy transfer process between Tb³⁺ and Eu³⁺ was resonant type via dipole–dipole mechanism, and the critical distance calculated by the concentration quenching method was found to be 17.61 Å. The stark splitting of Eu³⁺ emission lines and luminescence asymmetric ratio reveals the occupation of highly asymmetric site by the Eu³⁺ in the orthorhombic lattice. The variation in the emission intensities of the two strong emission peaks at 545 nm (green) and 612 nm (red) induces the multi-color emission in the samples by which the emission color of the phosphor be fine-tuned from green through white and eventually to red by adjusting the doping concentration of Eu³⁺ through energy transfer. The results indicated that Tb_2−xEu_x(MoO₄)₃ nanophosphor may serve as a multicolor-tunable phosphor and find potential application in smart optoelectronic devices.