Influence of microwave hydrothermal reaction factor on the morphology of NaY(MoO4)2 nano-/micro-structures and luminescence properties of NaY(MoO4)2:Tb3+

Abstract

The reaction conditions including exterior and interior factors in hydrothermal syntheses play very important roles. In this work, the influences of pH, Cit³⁻/Ln³⁺ and MoO₄²⁻/Ln³⁺ on the crystal structure and morphology of NaY(MoO₄)₂ microstructures derived from a microwave hydrothermal synthesis were systematically studied. It was found that certain morphologies of the NaY(MoO₄)₂:Tb³⁺ particles were only formed at critical pH values, and different amounts of Na₃Cit and Na₂(MoO₄)₂ in the reaction solution functioned in opposite ways in the crystal nucleation and growth. We also proposed that the competitive equilibrium between Na₃Cit and Na₂(MoO₄)₂ was responsible for the self-assembly behavior of the NaY(MoO₄)₂:Tb³⁺ nano-/micro-crystals. Based on the possible growth mechanism of the NaY(MoO₄)₂ microstructures, additional Cit³⁻/MoO₄²⁻/Ln³⁺ molar ratios for preparing the target products were designed and the corresponding samples were prepared. It was proven that the self-assembly behavior of the NaY(MoO₄)₂:Tb³⁺ crystals can be successfully modified under certain Cit³⁻/MoO₄²⁻/Ln³⁺ molar ratios. We also discovered that the morphology can slightly affect the luminescence intensity of the NaY(MoO₄)₂:Tb³⁺ phosphors. The temperature and concentration quenching behaviors of the NaY(MoO₄)₂:Tb³⁺ phosphors were studied. The crossover process was found to be responsible for the temperature quenching of ⁵D₄ fluorescence, and the electric dipole–dipole interaction was proven to be the physical nature of the concentration quenching and the fluorescence decay process.