Controllable synthesis of Ln3+ (Ln = Tb, Eu) doped zinc phosphate nano-/micro-structured materials: phase, morphology and luminescence properties

Abstract

Ln³⁺ (Ln = Tb, Eu) doped zinc phosphate tetrahydrate (ZPT:Ln³⁺) and ammonium zinc phosphate (AZP:Ln³⁺) nano-/micro-structured materials were synthesized in aqueous solution without the addition of any structure-directing agent. The phase structures, morphologies and luminescence properties of the as-synthesized samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy and lifetime. These investigations indicate that different phosphate sources M_nH_(3−n)PO₄ (M = NH₄⁺ or Na⁺, n = 1, 2, 3) can lead to the altering of morphology from nanosheet to microflower, but have no significant effect on the phase structure of the samples. The microlump, nanosheet, and microflower (constructed by the primary microlumps or nanosheets) of orthorhombic ZPT:Ln³⁺ could be selectively prepared by adjusting the pH value from 3.5 to 7.0. A mixture of orthorhombic ZPT:Ln³⁺ and monoclinic AZP:Ln³⁺ with a microflower morphology was obtained when the pH value was adjusted to 8.0. Monoclinic AZP:Ln³⁺ microplate, microcube and nanoparticle morphologies were obtained at pH values of 8.5, 9.0 and 11.0 respectively. The phase transformation and growth mechanism of the diverse morphologies were proposed, and ZPT:Ln³⁺ (Ln³⁺ = Eu or Tb) samples exhibit red or green emission under the excitation of UV light.