Hydrothermally derived NaLuF4:Yb3+, Ln3+ (Ln3+ = Er3+, Tm3+ and Ho3+) microstructures with controllable synthesis, morphology evolution and multicolor luminescence properties

Abstract

A series of NaLuF₄:Yb³⁺, Ln³⁺ (Ln³⁺ = Er³⁺, Tm³⁺, and Ho³⁺) microstructures with diverse morphologies and sizes were successfully prepared via a designed hydrothermal route with the assistance of trisodium citrate (Na₃Cit). The phases, morphologies, sizes and luminescent properties of the as-prepared products were fully characterized by means of X-ray diffraction (XRD), field scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and up-conversion (UC) photoluminescence spectroscopy, respectively. It can be found that the as-prepared microcrystals can be rationally modified in phase, size and morphology by tuning the pH value, Na₃Cit content, and reaction time. Based on the experimental results, the possible formation mechanism of the crystal growth process was proposed. Moreover, a systematic study of the up-conversion (UC) luminescent properties of NaLuF₄ has also been performed through doping different rare earth ions (Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺ and Yb³⁺/Ho³⁺). It is found that under 980 nm NIR excitation, the emission intensity and the corresponding luminescent colors of Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺, and Yb³⁺/Ho³⁺ co-doped NaLuF₄ can be precisely modulated by changing the Yb³⁺ doping concentration. These merits of multicolor emissions in the visible region endow this kind of material with potential applications in the fields of light display systems, lasers, and optoelectronic devices.