Highly uniform and monodisperse GdOF:Ln3+ (Ln = Eu, Tb, Tm, Dy, Ho, Sm) microspheres: hydrothermal synthesis and tunable-luminescence properties

Abstract

GdOF:Ln³⁺ (Ln = Eu, Tb, Tm, Dy, Ho and Sm) microspheres (1.5 μm) with high uniformity and monodispersity have been synthesized via a facile hydrothermal method followed by heat treatment (600 °C). X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as photoluminescence (PL) and cathodoluminescence (CL) spectra are used to characterize the resulting samples. A series of controlled experiments indicate that sodium citrate (Cit³⁻) as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the dosage of Cit³⁻ and pH values in the initial solution. The possible formation mechanism for these microspheres has been presented. Under UV light and low-voltage electron beam excitation, GdOF:Ln³⁺ microspheres show the characteristic f–f transitions of Ln³⁺ (Eu, Tb/Ho, Tm, Dy and Sm) ions and give bright red, green, blue, yellow and yellowish-orange emission, respectively. In addition, multicolored luminescence containing white emission have been successfully confected for co-doped GdOF:Ln³⁺ phosphors by changing the doped Ln³⁺ ions and adjusting their doping concentrations due to the simultaneous luminescence of Ln³⁺ in the GdOF host, making these materials have potential applications in field-emission display devices.