Synthesis, characterization and formation mechanism of Gd₂O₂S:Pr³⁺,Ce³⁺ phosphors by sealed triple-crucible method

Ln(NO3)3 · 6H2O (Ln = Gd, Pr and Ce), urea, sodium sulfite (Na2 SO3) and carbon powder were used as the starting materials. The precursor was synthesized with Ln(NO3)3 · 6H2O (Ln = Gd, Pr and Ce) solutions and urea at 95 °C for 4 h, and then the Gd2O2 S:Pr3+,Ce3+ phosphors were prepared by calcined the precursor (in inner crucible), Na2 SO3 (in middle crucible) and carbon powder (in outer crucible) at 1000 °C for 2 h in a sealed environment. The X-ray powder diffraction (XRD) results confirm that the as-synthesized Gd2O2 S phase has high purity and without the presence of any impurities. The field emission scanning electron microscopy (FE-SEM) inspection shows the morphology of Gd2O2 S:Pr3+,Ce3+ is hexagonal in shape and about 1 μm in size. The photoluminescence (PL) spectra under 301 nm ultraviolet (UV) light excitation shows a strong green emission at 513 nm. The quenching concentration occurs at Pr3+ ions concentration of 0.2% and its corresponding Commission Internationle de L’Eclairage (CIE) coordinates is (0.0273, 0.7921). The decay lifetimes are τ1 = 0.248 μs and τ2 = 1.824 μs for the Gd2O2 S:0.2%Pr3+,Ce3+ phosphor. The Gd2O2 S:0.2%Pr3+,Ce3+ phosphor film has excellent performance in the light utilization and the charge-transfer capability under 270 nm UV light radiation.