A template-free solvothermal synthesis and photoluminescence properties of multicolor Gd2O2S:xTb3+, yEu3+ hollow spheres

Abstract The multicolor Gd 2 O 2 S: x Tb 3+ , y Eu 3+ hollow spheres were successfully synthesized via a template-free solvothermal route without the use of surfactant from commercially available Ln (NO 3 ) 3 ·6H 2 O (Ln = Gd, Tb and Eu), absolute ethanol, ethanediamine and sublimed sulfur as the starting materials. The phase, structure, particle morphology and photoluminescence (PL) properties of the as-obtained products were investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectra. The influence of synthetic time on phase, structure and morphology was systematically investigated and discussed. The possible formation mechanism depending on synthetic time t for the Gd 2 O 2 S phase has been presented. These results demonstrate that the Gd 2 O 2 S hollow spheres could be obtained under optimal condition, namely solvothermal temperature T  = 220 °C and synthetic time t  = 16 h. The as-obtained Gd 2 O 2 S sample possesses hollow sphere structure, which has a typical size of about 2.5 μm in diameter and about 0.5 μm in shell thickness. PL spectroscopy reveals that the strongest emission peak for the Gd 2 O 2 S: x Tb 3+ and the Gd 2 O 2 S: y Eu 3+ samples is located at 545 nm and 628 nm, corresponding to 5 D 4 → 7 F 5 transitions of Tb 3+ ions and 5 D 0 → 7 F 2 transitions of Eu 3+ ions, respectively. The quenching concentration of Tb 3+ ions and Eu 3+ ions is 7%. In the case of Tb 3+ and Eu 3+ co-doped samples, when the concentration of Tb 3+ or Eu 3+ ions is 7%, the optimum concentration of Eu 3+ or Tb 3+ ions is determined to be 1%. Under 254 nm ultraviolet (UV) light excitation, the Gd 2 O 2 S:7%Tb 3+ , the Gd 2 O 2 S:7%Tb 3+ ,1%Eu 3+ and the Gd 2 O 2 S:7%Eu 3+ samples give green, yellow and red light emissions, respectively. And the corresponding CIE coordinates vary from (0.3513, 0.5615), (0.4120, 0.4588) to (0.5868, 0.3023), which is also well consistent with their luminous photographs.