Chemical co-precipitation synthesis and photoluminescence of Eu³⁺ or Dy³⁺ doped Zn₃Nb₂O₈ microcrystalline phosphors from hybrid precursors

Abstract

Dy³⁺, Eu³⁺ activated Zn₃Nb₂O₈ phosphors were synthesized via a modified chemical co-precipitation technology with the different concentration. In order to obtain the hybrid precursors, the rare earth coordination polymers with salicylic acid were used as precursors and the polyethylene glycol (PEG) was used as dispersing media. Their microstructure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and scanning electronic microscope (SEM), which indicates that there exist some novel column-like microcrystalline particles with 0.5–5.0 μm sizes in dimension. The characteristic transition of Dy³⁺ and Eu³⁺ were identified in the emission spectra and the optimum concentration of activators in Zn₃Nb₂O₈ was found.

Introduction

Recently, the development of flat electroluminescent, plasma, or field emission displays with huge industrial applications has increased the demand for materials with increasingly better characteristics in term of stability, brightness and industrial procession ability [1], [2]. Some work has been shown that rare earth orthoniobate has been extensively used as a host for X-ray luminescent materials. Besides this, lithium niobates (LiNbO₃) doped with transition metals or rare earth elements have been extensively studied for holographic data storage and other applications [3], [4], [5]. Rare earth ions, especially Eu³⁺ and Dy³⁺ are very important activators for the luminescent materials. The red emission of Eu^{3+ 5}D₀ → ⁷F₂ and the yellow emission of Dy^{3+ 4}F_9/2–⁶H_13/2 are hypersensitive with ΔJ = 2, which are affected strongly by the outside surrounding [6], [7]. LiNbO₃:Eu³⁺ polycrystalline powders were prepared by the sol–gel method and was studied that strong red emission deriving from Eu³⁺ ions was observed under pulsed infrared laser irradiation at 936.0 nm [8]. Besides this, the luminescence and energy transfer processes in La₂O₃–Nb₂O₅–B₂O₃:M³⁺ (M = Bi, Eu, Dy) glasses were investigated using luminescence spectroscopy, resulting that energy transfer from niobate groups to the lanthanide ions was observed for Eu³⁺, but not for Dy³⁺ [9]. Except for the selecting of host lattice, the fabrication of phosphor materials with particle size distribution, nonaggregation, fine size and good morphology is also a key issue faced by synthetic inorganic compounds [10], [11], [12]. Recently, the development of new wet chemical methods for the preparation of micron or submicron or nanophosphors may increase the possibilities for high effective rare earth phosphors [13], [14], [15], [16], [17], [18]. The sol–gel technology based on hydrolysis and polycondensation process is the most popular, which has been verified to be very useful in the preparation of nonagglomerated nanoparticles with surface accessibility for treatments and the ability to be used in thin-film techniques related to the sol–gel process [19], [20], [21], [22]. But in most cases, they synthesized luminescent materials doped with rare earth ions have been prepared through solid-state reactions at temperatures above 1300 °C or other traditional [23], [24]. At present, we have put forward a modified in situ co-precipitation technology to synthesize rare earth phosphors by assembling multicomponents inorganic/organic polymeric hybrid precursors and have succeeded in the preparation for some rare earth phosphors systems [20], [21], [22], [25], [26], [27].

In this paper, Eu³⁺ or Dy³⁺ activated with Zn₃Nb₂O₈ microcrystalline phosphor particles with different doping concentration were fabricated from hybrid precursors. Rare earth coordination polymers with ortho-hydroxylbenzoic acids were used as the precursors of luminescent rare earth species (Eu). Organic polymer, polyethylene glycol (PEG) as dispersing medium template, and the hybrid polymeric precursors were assembled with niobate source components Nb₂O₅ for NbO₄³⁻ group and Zn(Ac)₂·2H₂O. Then, through in situ co-precipitation process, the multicomponent hybrid precursors has been prepared and was calcinated at 1000 °C for 4 h to obtain the samples whose luminescent properties has been discussed in details.